I/M Lookup Table Update
EPA-420-B-00-100

October 2000

Transportation and Regional Programs Division

U.S. Environmental Protection Agency

Prepared for EPA by

Sierra Research, Inc. 

EPA Contract No. 68-C7-0051

Work Assignment No. 2-03

I/M Lookup Table Update
DISCLAIMER NO. 1

The accuracy of the information contained in this database has not been

verified by some of the manufacturers of the vehicles. Inaccuracies

regarding drivetrain configuration (e.g., two-wheel versus four-wheel

drive) and other parameters could affect the safety of dynamometer testing. 

In addition, the failure to properly identify vehicles with “traction control”

systems could lead to excessive stress on vehicle components during

dynamometer testing. To minimize the risks associated with such

inaccuracies, it is recommended that vehicles be adequately restrained

during dynamometer testing until the validity of the information in the

database has been confirmed. To minimize the risk of damage to vehicles,

it is recommended that drivers be trained to detect the drive configuration

of all vehicles and to recognize when a traction control system is present.

DISCLAIMER NO. 2

Although the information described in this report has been funded wholly

or in part by the United States Environmental Protection Agency under

Contract No. 68-C7-0051, it has not been subjected to the Agency’s peer

and administrative review and is being released for information purposes

only. It therefore may not necessarily reflect the views of the Agency and

no official endorsement should be inferred.
I/M LOOKUP TABLE UPDATE

Table of Contents

page

1. Introduction ........................................................1

2. Sources of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

EPA Certification Database . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Manufacturer Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Federal Register Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Vehicle Manufacturers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Small-Volume Manufacturers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1968–1972 Model Year Data ...........................................8

Default Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Manufacturer Fuel Economy Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Miscellaneous Additional Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3. Database Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Lookup Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Database Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4. Computational Methodologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

1979 and Newer Vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Pre-1979 Model Year Vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

5. Lookup Table Updates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

1999 Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Evaporative Fuel Inlet Pressure Test Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Other Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
-iiList of Tables

page

1. EPA Certification Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2. Manufacturers Contacted Regarding Vehicle Testability......................7

3. Format of EPA I/M Lookup Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4. Data Sources for EPA I/M Lookup Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5. Light-Duty Truck Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
*

 “IM240 & Evap Technical Guidance,” U.S. Environmental Protection Agency, EPA420-R-00-007, April

2000, and “Acceleration Simulation Mode Test Procedures, Emission Standards, Quality Control

Requirements, and Equipment Specifications,” U.S. Environmental Protection Agency, EPA-AA-RPSDIM-96-2, July 1996.

1. INTRODUCTION

A number of states have implemented enhanced vehicle emissions inspection and

maintenance (I/M) programs. Vehicles subject to enhanced I/M have exhaust emissions

measured while undergoing “loaded mode” testing, i.e., in which the vehicle is driven on

a standard driving cycle on a chassis dynamometer. One or a combination of the possible

driving cycles listed below are currently being used in the enhanced I/M programs.

1. A 240-second, stop-and-go driving (transient) test called the “IM240.”

2. Shorter transient test cycles such as the IM93, IM147 (which are both subsets of

the IM240), or BAR31 tests.

3. A shorter, steady-state test called the “Acceleration Simulation Mode” (ASM)

2525, designed to simulate acceleration during in-use vehicle operation. Although

ASM tests are run at a steady speed, the dynamometer is set to load the vehicle

more than if the vehicle were cruising at a steady speed. “ASM2525” is run at

25% of the load required to accelerate at 3.3 mph/sec (the maximum acceleration

rate on the FTP) at a speed of 25 mph.

4. A second ASM test mode called the “ASM5015.” “ASM5015” is run at 50% of

the load required to accelerate at 3.3 mph/sec (the maximum acceleration rate on

the FTP) at a speed of 15 mph. 

To efficiently use one or more of the above tests, an I/M test facility must be able to

quickly and easily adjust the chassis dynamometer power absorption and (in the case of

the IM240 or another transient test cycle) inertia weight settings for each vehicle, so that

the vehicle engine is properly loaded during testing. Under enhanced I/M test guidance

issued by EPA,*

 the dynamometer settings are to be automatically selected for each

vehicle, based on vehicle parameters entered into the test record by the I/M lane

inspector.

According to the enhanced test guidance, EPA is responsible for supplying an electronic

lookup table that can be used to automatically select the proper dynamometer settings for
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each particular vehicle. Under contract to EPA, Sierra Research developed and released

in September 1994 an initial version of the Lookup Table that contained both

dynamometer settings and purge/pressure testability data. Subsequent versions have also

been prepared and released by Sierra for EPA. This report addresses Sierra’s latest

release (Version 1.8.4) of the Lookup Table. Changes incorporated into Version 1.8.4 of

the table include the addition of 1999 model-year vehicles, deletion of data on alternative

test pressures for conducting the fuel inlet vehicle evaporative control system integrity

(pressure) test, deletion of heavy-duty vehicle data records, correction/addition of test

parameters based on a detailed comparison with I/M test data provided by the state of

Virginia and other independent sources of data, and other miscellaneous updates. 

Section 2 of this report provides background on the sources of data used to construct and

update the electronic Lookup Table. Section 3 describes the format of the database and

Section 4 contains the computational methodologies used to construct it. Section 5

provides additional details on the changes incorporated into Version 1.8.4 of the table.

###
-3-

2. SOURCES OF DATA

Several sources were accessed to obtain necessary vehicle parameter data. Each of these

sources is discussed below, along with a description of the data obtained from each

source. 

EPA Certification Database

The primary source of information used to initially develop the Lookup Table was

certification data obtained from EPA’s certification databases located on the Wayne State

University mainframe computer in Detroit, Michigan. Pertinent data from this source are

described in Table 1. The listed data were provided by EPA for 1981 and later model

year vehicles (data on curb weight, rather than equivalent test weight, were provided for

some models). In addition, incomplete data for model years 1978–1980 were also

provided. For example, vehicle coastdown times were not provided for most of the

1978–1980 models. 

Determination of Model Names - The EPA certification data described above contain

certain model names that are listed in a very cryptic fashion. Cryptic model codes for

GM, Toyota, and New United Motor Manufacturers Inc. (NUMMI) models are used

extensively in the database. Manufacturers of other models identified by coded name

include Chrysler, Ford, Fuji, Isuzu, and Suzuki (Ford and Fuji used cryptic names before

1983 only). Because I/M inspectors will use publicly known model names to identify

vehicles brought in for testing, a method was needed to convert the model codes

contained in the certification database into the proper model names. Accordingly,

additional certification data (for 1979 and later models) containing a “carline code” field

and another database containing a carline code decoder were obtained from EPA. This

information was used to decode most of the model codes.

A SAS program was created to read in the additional certification data and the carline

code decoder database. The two data sets were merged by model year and carline code to

create one data set (for model years 1979–1993) containing the following vehicle

parameters: model year, manufacturer, engine family, model name, equivalent test

weight, axle ratio, test vehicle type, and transmission configuration. 

The program then read in all the certification data initially provided by EPA, and kept

only the vehicles associated with the manufacturers using the carline codes. It also

determined whether each model’s transmission type was manual, automatic, or either.
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Table 1

EPA Certification Data

• Model year (MDYR)

• Manufacturer (MFR)

• Model (MODL)

• Vehicle type (VTYP)

• Sales class (SACL)

• Altitude code (ALTC)

• Engine type (ETYP)

• Fuel type (FTYP)

• Engine family (ENFM)

• Evaporative family (EVFM)

• Coastdown time (VCDT)

• Displacement (DISP)

• Number of cylinders (#CYL)

• Drive axle weight/full (VAXF)

• Drive axle weight/empty (VAXE)

• Evaporative system type (EVSY)

• Main fuel tank capacity (MTNK)

• Auxiliary fuel tank capacity (ATNK)

• Model code (MDCD)

• Drive type (DRCD)

• Axle ratio (AXLR)

• Transmission configuration (VTRN)

• EPA test type (TTYP)

• Equivalent test weight (ETW)

The combined carline/certification data set and the additional certification data set were

merged by model year, manufacturer engine family, and equivalent test weight. This

process gave an excellent match between the certification data set and the model names,

with only 21 engine family/model records not able to be identified. A subsequent attempt

was made to match these outstanding records with engine family/model combinations

identified in additional certification data (described below) published annually in the

Federal Register. 

The outstanding records were matched to possible model names. Because a single data

record in the Federal Register data set can represent several different models, multiple

records were generated in the engine-family-specific vehicle parameter database for most

of the outstanding certification records, with a separate record corresponding to each

possible model. 
*

 At the time the first version of the Lookup Table was developed, the 1993 model year was the most recent

for which Federal Register data were available. Subsequent updates to the table have been based on

electronic copies of the vehicle certification and fuel economy data provided directly to Sierra by EPA

technical staff. 

-5-

Review of model names in the two certification data sets revealed a significant number of

errors and inconsistencies in model naming convention. Accordingly, a list of common

“publicly known” model names was created and merged with the two data sets to

eliminate inconsistent entries. The resulting model names were used in the Lookup Table

to replace corresponding model names and/or codes. 

Manufacturer Identification

A separate list of manufacturers was provided by EPA for use in the database. This list,

which includes both the full name and a two-character “EPA Manufacturer Subcode” for

each listed manufacturer, is contained in the Society of Automotive Engineers’ (SAE’s)

J2008 recommended organization of vehicle service information. These names and

subcodes were merged with the four-character manufacturer abbreviation included in the

EPA certification data to convert the abbreviations to the full names and subcodes

contained in SAE J2008. The resulting subcodes and full names are included in fields 2

and 3, respectively, of the Lookup Table.

For some manufacturers, no match was found between the certification database codes

and entries on the SAE J2008 list. This was particularly true for manufacturers of older

models, some of whom may not be in business at present. For such vehicles, the full

name of the manufacturer (if it could be determined) or (at a minimum) the manufacturer

abbreviation included in the EPA certification database was included in field 3 of the

Lookup Table. Field 2 has been left blank for these vehicles.

Federal Register Data

EPA certification data for each model year are also published annually in the Federal

Register. Based on discussions with EPA’s Freedom of Information Officer at

Ann Arbor, it was learned that these data were available in electronic format for model

years 1979–1993.* These data included the following applicable vehicle parameters:

• Model year;

• Manufacturer;

• Model description;

• Engine family;

• Engine displacement;

• Transmission type;
*

 Equivalent test weight, rather than inertia weight class, was recorded for 1980 and later models.

** This value was recorded only for 1983 and later models.

*** The Federal Register data are a compilation of the results of certification tests submitted by the vehicle

manufacturers. Test results may be submitted for one or more “certification” vehicles considered

representative of a group of models containing the same engine family.

-6-

• Inertia weight class;* and

• Actual dynamometer horsepower.**

A program was developed to convert these data into standard ASCII text files. (As

provided by EPA, they were formatted in tabular fashion identically to how they appear in

the Federal Register.) This approach is summarized below.

Federal Register Data Retrieval - A FORTRAN program was written to read Federal

Register data files and print out the year, manufacturer, vehicle type, model name, engine

family, emission control system entries, engine displacement, fuel delivery system,

transmission type, equivalent test weight (ETW), and “actual” dynamometer horsepower. 

The program results in a listing that includes each model associated with an engine

family, along with the ETWs listed for each certification vehicle used for a particular

group of models.*** If an engine family has two possible displacements, there would also

be separate records created for each displacement. For example, 30 separate data records

would be created for an engine family with 5 possible models, 3 different ETWs, and 2

displacements, each with a different combination of model, ETW, and displacement. If

both a manual and automatic transmission were listed for a certain engine family test, the

transmission-type entry would be listed in the record as “E” (for either). Otherwise, the

transmission type would be labeled as either “M” for manual or “A” for automatic.

The resulting Federal Register data were merged into the vehicle parameter database. In

addition, Federal Register certification data for the 1973–1978 model years, which were

not available electronically, were entered manually and merged into the vehicle parameter

database as well. Records from the two certification data sources (EPA and the Federal

Register) were compared on the basis of model year, manufacturer, model name, and

engine family. Federal Register records that had identical entries to EPA records in these

four fields were deleted from the database, since the ETW data contained in the EPA

database are more accurate than those contained in the Federal Register data. (The ETWs

contained in the EPA data are specific to the vehicle-engine family combination

identified in each record, whereas ETWs in the Federal Register data are based on the

certification vehicles considered to be representative of a group of vehicle-engine family

combinations.)

This methodology resulted in the use of Federal Register certification data for those

vehicle-engine family combinations (i.e., 1973–1978 models plus some later model

vehicles) for which no records were available in the EPA certification database.
-7-

Vehicle Manufacturers

In addition to the certification data obtained above, additional data related to vehicle

testability were obtained directly from the manufacturers listed in Table 2. These

manufacturers were asked to provide the following information related to the testability

of their models:

• Traction control present;

• Manual traction control disablement possible; 

• Anti-lock braking (ABS) present; 

• Anti-lock braking disablement possible; 

• Four-wheel-drive present;

• Full-time four-wheel-drive; and

• Relevant evaporative control system design information. 

Table 2

Manufacturers Contacted

Regarding Vehicle Testability

• BMW

• Chrysler

• Ford

• General Motors

• Honda

• Hyundai

• Isuzu

• Mazda

• Mitsubishi

• Nissan

• Saab

• Subaru

• Toyota

• Volkswagen

• Volvo
*

 The approach used to consolidate the full vehicle parameter data set into the Lookup Table data set is

described in Section 3.

-8-

Vehicle testability data received from the manufacturers were incorporated into the

vehicle parameter database and the consolidated Lookup Table.*

 Possible entries are “Y”,

“N”, “M”, and “U”, for yes, no, maybe, and unknown, respectively. “U” was entered for

those models for which no data were received. “M” entries were entered into the vehicle

testability fields for those models that may or may not be equipped with the various

systems described above. 

The “M” category is particularly applicable to the Lookup Table, since the aggregated

vehicle records included in that database may contain a combination of vehicles, some of

which are equipped with these systems and some of which are not. An “M” would also

be entered for those models on which one of the above systems (e.g., ABS) was offered

as an option by the manufacturer. As noted during the September 13, 1994 meeting of

the IM240 Test Parameter Subcommittee meeting, ABS and/or traction control systems

may be offered as options on a wide range of models and model years, depending on the

manufacturer. For such vehicles, a determination will need to be made at the time of

inspection as to whether a particular vehicle is equipped with traction control.

Manufacturer Review of Lookup Table - Several manufacturers have reviewed the

various releases of the Lookup Table, and provided corrections and additions to the data. 

This includes the three domestic manufacturers (i.e., General Motors, Ford, and Chrysler)

as well as some of the foreign manufacturers. These modifications are included in

subsequent versions of the table. 

Small-Volume Manufacturers

Data from small-volume manufacturers (those producing fewer than 5,000 vehicles per

year) are not included in the certification database provided by EPA. They are, however,

included in the Federal Register data set. Available Federal Register data for 1973-1993

models produced by small-volume manufacturers were therefore included in the initial

version of the Lookup Table. Since subsequent updates to the table have been based

primarily on certification data provided directly to Sierra by EPA, 1994 and later models

produced by small-volume manufacturers are not included.

1968–1972 Model Year Data

No certification data, from either the EPA databases or the Federal Register data, were

available for 1968–1972 model year vehicles. Because of the extremely limited nature of

available data from other sources (e.g., annual Automotive News Marketing Data Books
*

 “Vehicle Manual: 1972-1978,” Automotive Testing Laboratories, Inc., undated.

** “Default IM240 Dynamometer Loading, Test Weights, and Tire Losses,” U.S. EPA, June 7, 1995.

*** “ASM2 Procedures and Equipment Specifications, Ver 1.5,” U.S. Environmental Protection Agency,

July 6, 1995.

-9-

Lower Limit

t

n = − ×

μ

σ

and a listing* of 1972 models compiled and provided to Sierra by Automotive Testing

Laboratories [ATL]), these data are not included in the Lookup Table. 

Default Parameters

Default dynamometer parameters, which can be used in cases where model identification

is impossible, were also developed. For Version 1.1 of the Lookup Table, track road-load

horsepower (TRLHP) and inertia weight default values contained in

Section 85.2221(c)(5) of an earlier version of EPA’s high-tech guidance were used. 

(TRLHP settings for inertia weights of 5500 and 6000 lbs were linearly extrapolated from

the data contained in Section 85.2221(c)(5), which include inertia weights only up to

5000 lbs.) For Versions 1.2 through 1.5.1, the IM240 default values were modified based

on a revised list of defaults** provided by EPA. In addition, ASM default values

developed by EPA*** were incorporated. The revised default values included TRLHP and

generic tire/roll losses (GTRL) on both 8.625” and 20.0” diameter dynamometer rolls. 

These values were disaggregated according to both vehicle body style and either number

of cylinders or vehicle test weight.

As part of the development of Version 1.6.1 of the Lookup Table, EPA directed Sierra to

review and determine if the defaults contained in the table should be updated. An

analysis was therefore conducted of the existing default values. Existing Lookup Table

entries were sorted according to body shape, number of cylinders, and model year

grouping. Five model year groups were selected: 1973–80, 1981–84, 1985–89, 1990–94,

and 1995–97. These groups were chosen on a relatively arbitrary basis to determine the

degree of variance and trends in TRLHP and ETW values among model years.

Assuming the observations were normally distributed within each analysis category (i.e.,

body shape/#cylinders/model year group combination), lower-limit confidence intervals

were then calculated for TRLHP and ETW in each category using a Student’s-t test as

follows. Using lower-limit intervals of 5% and 20% recommended by EPA (meaning

that 95% and 80%, respectively, of all observations occur above the interval), appropriate

t-values were looked up from a standard statistical table as a function of sample size n

(e.g., t5% for large n is 1.645). The lower limit values for TRLHP and ETW were then

calculated using the following equation:
-10-

where μ and σ are the sample mean and standard deviation, respectively, and t and n are

defined as above.

TRLHP and ETW values resulting from these lower-limit metrics are thus considered

conservative, since they represent underloading of most vehicles in each range. 

Several observations were drawn from the results of the above analysis:

• Some shape/cylinder categories exhibited a significant spread in TRLHP and

ETW values across the model year ranges, while others did not. 

• There did not appear to be any predominant trend in TRLHP values over time

(i.e., they do not all decline or increase with increasing model year). 

• With few exceptions, ETW values appeared to generally increase with model year

(i.e., newer models are heavier on average for a given shape and number of

cylinders).

• There were significant differences in the existing defaults contained in the Lookup

Table, and the 5% and 20% lower-limit intervals.

• A limited number of other year/shape/cylinder categories contained no applicable

data records.

• In almost all cases, there was little difference in the 5% and 20% lower-limit

intervals for either TRLHP or ETW.

It was also noted that no defaults currently exist in the Lookup Table for rotary engines. 

TRLHP values associated with rotary engine-equipped vehicles appear roughly

comparable to those of four-cylinder vehicles. However, ETW values for the rotary

vehicles are heavier than the four-cylinder vehicles.

Based on the above results, a decision was made to develop and incorporate updated

default values into Version 1.6.1 of the Lookup Table. The approach chosen to create the

updated defaults included the following elements:

1. New TRLHP and ETW defaults would be developed based on the 20% lowerlimit intervals. Revised ETW defaults would be rounded to the nearest 250

pounds.

2. Model-year-specific defaults would be developed to replace the previous single

set of defaults contained at the beginning of the first (1973–1978 model year)

Lookup Table file. Defaults for year/shape/cylinder containing no data records

would be developed from neighboring model years. Model-year-specific defaults

would not be included for year/shape/cylinder combinations not manufactured in

those years.
*

“VIN-Based Lookup Table,” prepared for U.S. Environmental Protection Agency, Sierra Research, Inc.,

Report No. SR97-10-01, October 13, 1997.

-11-

3. Default values for rotary engines would be added to the Lookup Table.

Model-year-specific defaults are now included at the beginning of each model year

grouping in the table. To avoid confusion with the previous default values, new Lookup

Table vehicle identification codes (or “index numbers”) have been developed for all

defaults. The convention used for the index numbers contained in the default records is

MY99XX. For example, the first default value for the 1973 model year would have an

index number of 739901, the second 739902, and so on.

Manufacturer Fuel Economy Data

As noted in Sierra’s 1997 report* to EPA on the Lookup Table, a comparison of EPA

certification data with other sources of vehicle model and test weight information shows

that use of the certification data as the principal source of information has introduced

some errors into the table. This finding is also supported by comments received from

some of the manufacturers. It is primarily because the certification data do not include a

full listing of all models actually sold by the manufacturers in a particular model year. In

addition, it is apparent that some models that were certified were never actually sold.

As a result of this finding, Sierra recommended to EPA in 1997 that future efforts to

update the Lookup Table be based on fuel economy data that the manufacturers must

submit to EPA. Unlike the certification data, the fuel economy data contain a complete

listing of dynamometer parameters for all models sold by each manufacturer. 

At roughly that same time (i.e., circa 1997), EPA also transferred its certification and fuel

economy data from the Wayne State databases mentioned previously to an in-house interrelational database system called the Certification and Fuel Economy Information System

(CFEIS). This contractor-developed Oracle-based system is maintained by EPA staff. 

While EPA technical staff concurred with Sierra’s 1997 recommendation to use

manufacturer fuel economy data as the primary basis for future updates to the Lookup

Table, the switch to the CFEIS system has complicated this transition. According to EPA

database staff, the inter-relational nature of the CFEIS system makes it somewhat difficult

to determine the exact source (i.e., certification or fuel economy submittals) of data

elements extracted from the system. EPA is continuing to investigate this issue, with the

intent being to migrate as soon as possible to using fuel economy data as the primary

source of data for new model year vehicles in future releases of the Lookup Table.
*

 Tier One data for 1988-1995 models produced by domestic manufacturers were included in Version 1.1

of the Lookup Table. These data were expanded in Version 1.2 to include imported vehicles and the older

domestic models.

** “All Wheel Drive/Traction Control Guide,” Colorado Department of Public Health and Environment,

June 1995.

***As discussed in more detail in Section 5, these data have been deleted from Version 1.8.4 and

subsequent versions of the Lookup Table.

-12-

Miscellaneous Additional Sources

Additional ABS and traction control data were also obtained from Tier One, a market

research firm specializing in automotive electronics. The Tier One data, which included

detailed information disaggregated by make, model, model year, and vehicle platform,

were input to the Lookup Table*

 for those manufacturers that did not supply data directly

to Sierra. In addition, data contained in an all-wheel-drive/traction control guide**

produced by the Colorado Department of Public Health and Environment were reviewed

and incorporated, where appropriate, into the Lookup Table.

Data on pressure testability status and canister location, obtained from the Louisville I/M

program, selected vehicle manufacturers (e.g., Chrysler), and All Data on-line automotive

service manuals, were also incorporated into Version 1.1 of the Lookup Table. 

Additional purge and pressure testability data (e.g., the appropriate level of pressurization

to be used) obtained from the vehicle manufacturers were included in subsequent

releases.*** In addition, gas cap adapter data (i.e., which adapters to use with which

vehicles) provided by Stant Manufacturing were incorporated into Version 1.4 and

subsequent releases of the table.

Several independent sources of information regarding vehicle models and test weights

were also accessed during development of Version 1.4 and subsequent releases of the

Lookup Table. These sources include the Kelly Blue Book, the Automotive News

Market Data Book, the Standard Catalog of Imported Cars, and the Standard Catalog of

American Light-Duty Trucks.

###
*

 The second and third fields both reference the vehicle manufacturer, with the second field being a

two-character code and the third the full name of the manufacturer.

**Vehicle identification codes were changed between Versions 1.1 and 1.2 of the Lookup Table. Versions

1.2 and later releases have consistent vehicle IDs. 

-13-

3. DATABASE FORMAT

A comprehensive vehicle parameter database, disaggregated to the engine family level,

was initially developed from the sources listed in Section 2. This data set was then

collapsed into a more aggregated data set, for distribution to I/M programs as an

electronic Lookup Table. The Lookup Table database is described below, followed by

detailed format specifications for the table. 

Lookup Table

The Lookup Table contains fields for data specified by EPA staff, as well as additional

data suggested by the I/M contractors (e.g., canister location). In some cases, data are not

currently available for certain vehicle parameters. Fields for these parameters are

included for future use, but have been left blank in the current version.

The first nine fields in each database record contain vehicle identification entries. These

fields are as follows:

1. Model year;

2. Manufacturer code;*

3. Manufacturer name;

4. Manufacturer division;

5. Public model name;

6. Body style (e.g., sedan, wagon, etc.);

7. Number of cylinders;

8. Engine displacement; and 

9. Transmission type. 

Following the above entries, each record contains a unique vehicle identification code,

which can be used to cross-reference the record with entries for the same vehicle listing in

other versions of the Lookup Table.**
*

Sales class entries have been simplified in Version 1.4 and subsequent releases of the Lookup Table to

simply identify whether a vehicle was certified as a passenger vehicle or truck.

-14-

Fields are then provided for the type of fuel burned by the vehicle (only gasoline-powered

and a relatively few alternatively fueled vehicles are currently included in the Lookup

Table), evaporative control system, and the number and location of evaporative canisters. 

A simple locational coding system for canister location has been developed, based on the

quadrant codes listed below.

1 = left front

2 = right front

3 = right rear

4 = left rear

M = multiple locations

While much more elaborate (e.g., x/y coordinate systems) locational systems could be

adopted, it is believed that a system that simply identifies general canister locations is

much more likely to be used by I/M inspectors. 

A field for the sales class of the vehicle*

 is then provided. This is followed by fields for

all required IM240 dynamometer settings, e.g., ETW, TRLHP, and 8.625” and 20.0”

GTRL. Because the Lookup Table is disaggregated only to the level described above, a

methodology for aggregating multiple ETW values into the database records contained in

the table has been developed and is explained below. Reasons for excluding certain

vehicle parameters from the Lookup Table are also discussed.

Methodology for Developing Test Parameters by Vehicle Category - In developing this

methodology, a review was conducted of the approach previously employed by EPA to

construct the Lookup Table used by ATL for IM240 testing in Hammond, Indiana, and

Phoenix, Arizona. Under that approach, ETW and TRLHP values were averaged to

obtain a value for each vehicle category. In cases of significant variation within a single

vehicle category, EPA used a somewhat subjective approach that attempted to select

ETW and TRLHP values between the minimum and maximum values for the category so

that (1) the values increased as engine size increased, and (2) there were no

“unreasonable” jumps in values from model year to model year.

An alternative approach to that previously used by EPA has been employed to develop

ETW values for each vehicle category. This methodology follows guidance provided by

EPA to use a conservative approach to compute the test parameters for each vehicle

category. EPA’s guidance indicated that (1) an engine should be underloaded, rather than

overloaded, in developing test parameters for the aggregated vehicle categories; and

(2) ETW is more important than TRLHP in setting the dynamometer test parameters. In

accordance with this guidance, the lowest ETW value in each vehicle category was used

for that category. (In cases where a vehicle category contained both EPA and Federal

Register certification data records, the lowest ETW from the EPA certification records

was used.) Vehicle coast down time (VCDT) and drive axle weights (VAXF and VAXE)
*

 Computational methodologies are described in Section 4.

** “ASM Horsepower Equations,” U.S. Environmental Protection Agency, July 1995.

***No acceptable tracer purge test has been approved by EPA at present.

-15-

corresponding to the selected ETW were then used to compute TRLHP and GTRL,

respectively.*

 In cases where a corresponding VCDT value was not included in the

certification database for a minimum ETW within a specific vehicle category, the VCDT

corresponding to the ETW value closest to the minimum was used. (A similar

methodology was used in the case of missing drive axle weight data.)

Following the IM240 dynamometer settings, similar dynamometer settings for the two

most common ASM test modes (ASM5015 and ASM2525) have been incorporated into

the Lookup Table, using formulas supplied by EPA.** Fields are then provided for

average drive axle weight, wheelbase, and drive layout code (e.g., front, rear, etc.). 

Following that are fields for fuel tank size (to aid in pressure testing) and dynamometer

testability (e.g., four-wheel-drive, traction control, and ABS status). 

In keeping with the conservative approach to aggregating test parameters discussed

above, the minimum fuel tank size for a specific vehicle within each vehicle category has

been assumed for that category as well. In cases of yes/no answers that vary across

engine families contained within a single vehicle category, an “M” (for maybe) entry has

been used to indicate the possibility of a particular option. For example, if a single

vehicle category includes both full-time and selectable four-wheel-drive vehicles, an “M”

would be entered in the full-time four-wheel-drive field. 

Fields are also included for location codes of the four-wheel-drive selector and manual

traction disablement switch. Version 1.7.2 of the Lookup Table was the first release to

include information provided by the manufacturers (i.e., Volkswagen) on the location of

the traction control disablement switch. It was therefore necessary to develop a standard

nomenclature for mapping the location of the switch. In consultation with Volkswagen, it

was decided to use the same mapping scheme as recently proposed for mapping the

location of the OBDII diagnostic link connector (DLC). This standardization of a single

mapping approach for identifying both items will help avoid inspector confusion in

finding the disablement switch and DLC on individual vehicles. 

A field is provided for entry of an upper fuel economy limit, for use as a quality control

check on the testing results. Following that are fields for the testability status of the

vehicle for the EPA and inlet pressure tests, and the EPA and tracer purge tests.***

Comment fields are also provided for each pressure and purge test, to allow entry of the

reason (if applicable) for a vehicle being untestable on that test. In addition, fields are

provided for minimum and maximum test pressures for the two pressure tests. As

discussed in more detail in Section 5, however, all alternative test pressures have been

deleted from the Lookup Table beginning with Version 1.8.2.
-16-

The next-to-the-last field contains the date of the record. There was some confusion in

the past regarding the convention used in modifying the date of each individual Lookup

Table record. Some users believed this date should change with each new version of the

Lookup Table and be consistent for all records contained in that version. Other users felt

the record date should only be changed for those records modified in that version of the

table (i.e., there would be no change of date if the record were not modified). They also

pointed out that each version of the Lookup Table has its own revision date and it makes

little sense to put the same date in all the individual records as well.

After considering this issue, Sierra recommended and EPA agreed that the date of record

will remain the same in succeeding versions of the table, unless a change is made to the

record. Any record in Version 1.8.4 that contains an updated date is therefore either new

or has been modified in some manner.

The final field is the gas cap adapter that should be used in testing the vehicle using the

Stant testing apparatus.

Database Format

Table 3 provides a detailed format listing for the Lookup Table. The data set is formatted

as a series of comma-separated, variable length ASCII text files. To keep the data set at a

manageable size, it has been divided into files of no more than 1 Mb in length. This has

resulted in five data files, covering the following model year ranges:

1. 1973–1978;

2. 1979–1984;

3. 1985–1990;

4. 1991–1996; and

5. 1997–1999.

To aid in proper field identification, comma-separated headings for each field have been

added as the first line in the five data files. The abbreviations used for each field heading

are included in Table 3.

Beginning with Version 1.6.1 of the Lookup Table, actual data values have been deleted

from certain of the Lookup Table fields. These include Fields 21, 23-25, 27-29, and 54. 

These fields are now marked as “reserved” in Table 3. 

Fields 19 and 20 have been redefined respectively as VINPLC and VINCHAR beginning

with Version 1.7.2 of the table. VINPLC indicates the location of the VIN digit that

identifies the GVWR range of certain makes of light-duty trucks (LDTs) that include

models both under and over 6000 lbs GVWR. VINCHAR includes all VIN characters

that represent LDTs with GVWRs of less than or equal to 6000 pounds. Additional

details on the contents of these fields are provided in Section 4.
* All fields are comma separated, variable length.

-17-

Table 3

Format of EPA I/M Lookup Table

Maximum

Field Length* Name Abbrev. Description

 1 2 Model Year MDYR alphanumeric (last 2 digits, DF=default re 2 2 Manufacturer Code MFRC alphanumeric (2-digit SAE J2008 abbrevi 3 40 Manufacturer Name MFRN alphanumeric (full name) 4 17 Manufacturer Division DIV alpha (full name) 5 23 Public Model Name PNAME alpha (commonly known name of model) 6 1 Body Style SHAPE numeric (1=sedan, 2=station wagon, 3=pi

4=sport/utility, 5=minivan, 6=full-size va

 7 2 No. of Cylinders NCYL alphanumeric (R = rotary) 8 3 Engine Displacement DISPLR numeric (liters, includes decimal, n.n) 9 1 Transmission Type TRANY alpha (M=manual, A=automatic, E=either 10 8 Vehicle Category ID VCID numeric, unique code for vehicles with id

first 8 fields

 11 1 Fuel Type FULTYPE numeric (1=gasoline, 2=natural gas, other 12 2 Evaporative System EVSYS numeric (0=not recorded, 1=crankcase, 2=

4=none, 5=canister+charcoal air cleaner, 99=other)

 13 1 No. of Evap Canisters NCAN alphanumeric (V=varies) 14 2 Location of Canisters LOCAN alphanumeric (1-4 = vehicle quadrant loc

FT=on fuel tank, M=multiple locations) 

 15 2 Sales Class SACL alphanumeric (V=vehicle, T=truck, E=eit 16 4 Equivalent Test Weight ETW numeric (lbs, nnnnn) 17 4 Inertia Weight Class IWC numeric (lbs, nnnnn)
* All fields are comma separated, variable length.

-18-

 Table 3 (continued)

Format of EPA I/M Lookup Table

Maximum

Field Length* Name Abbrev. Description

 18 4 Track Road-Load TRLHP numeric (hp, includes decimal, nn.n)

 Horsepower (50 mph)

 19 2 VIN Digit VINPLC numeric (nn) 20 8 VIN Character VINCHAR alphanumeric 21 1 (Reserved) 22 4 Tire/Roll Interface GTRL8 numeric (hp, includes decimal, nn.n) Losses on 8.625”

 Roll at 50 mph

 23 1 (Reserved) 24 1 (Reserved) 25 1 (Reserved) 26 4 Tire/Roll Interface GTRL20 numeric (hp, includes decimal, nn.n) Losses on 20.0”

 Roll at 50 mph

 27 1 (Reserved) 28 1 (Reserved) 29 1 (Reserved) 30 4 Total ASM5015 THP5015 numeric (hp, includes decimal, nn.n)

 Horsepower

 31 4 Total ASM2525 THP2525 numeric (hp, includes decimal, nn.n)

 Horsepower

 32 4 ASM5015 Horsepower HP50158 numeric (hp, includes decimal, nn.n)

 for 8.625” Roll
* All fields are comma separated, variable length.

-19-

 Table 3 (continued)

Format of EPA I/M Lookup Table

Maximum

Field Length* Name Abbrev. Description

 33 4 ASM2525 Horsepower HP25258 numeric (hp, includes decimal, nn.n)

 for 8.625” Roll

 34 4 ASM5015 Horsepower HP501520 numeric (hp, includes decimal, nn.n)

 for 20.0” Roll

 35 4 ASM2525 Horsepower HP252520 numeric (hp, includes decimal, nn.n)

 for 20.0” Roll

 36 4 ASM5015 Tire/Roll GTRL1508 numeric (hp, includes decimal, nn.n) Interface Losses

 on 8.625” Roll

 37 4 ASM2525 Tire/Roll GTRL2508 numeric (hp, includes decimal, nn.n) Interface Losses

 on 8.625” Roll

 38 4 ASM5015 Tire/Roll GTRL1520 numeric (hp, includes decimal, nn.n) Interface Losses

 on 20.0” Roll

 39 4 ASM2525 Tire/Roll GTRL2520 numeric (hp, includes decimal, nn.n) Interface Losses

 on 20.0” Roll

 40 4 Average Drive Axle Wt. DAXWT numeric (lbs, nnnn) 41 5 Wheelbase WHLBS numeric (inches, includes decimal, nnn.n) 42 1 Drive Layout Code DRLCD numeric (1=front drive, 2=rear drive, 3=s

4-wheel-drive, 4=full-time 4-wheel drive, 

 43 1 Full-time 4-Wheel? FWDS alpha (Y,N,M,U)
* All fields are comma separated, variable length.

-20-

Table 3 (continued)

Format of EPA I/M Lookup Table

Maximum

Field Length* Name Abbrev. Description

 44 1 Location of Four-Wheel LFWD alphanumeric (1-8 = vehicle location)

 Selector

 45 4 Main Fuel Tank Size MTNK numeric (gallons, nn.n) 46 1 Auxiliary Fuel Tank? ATNKQ alpha (Y=yes,N=no,M=maybe,U=unknow 47 4 Auxiliary Tank Size ATNK numeric (gallons, nn.n) 48 1 Traction Control? TC alpha (Y,N,M,U) 49 1 Traction Control TCS alpha (Y,N,M,U)

 Disablement?

 50 1 Disablement Switch LTC alphanumeric (1-8 = vehicle location)

 Location

 51 1 Anti-lock Braking? ABS alpha (Y,N,M,U) 52 1 ABS Disablement ABSS alpha (Y,N,M,U)

 Possible?

 53 1 2-Wheel-Drive Dyno DYNTST2 alpha (N,M)

 Testing Possible?

 54 1 (Reserved) 55 1 (Reserved) 56 3 EPA Pressure Test Status PRSTAT alpha (NOT, LOW, MED, HIG, ALT, C_ 57 3 EPA PT Comments PRSTCOM alpha (VLV, CLM, INA, PRT, UNK) 58 4 EPA PT Min. Pressure EPAMIN numeric (nn.n in of H20, includes decima 59 4 EPA PT Max. Pressure EPAMAX numeric (nn.n in of H20, includes decima 60 3 Inlet Pressure Test Status PRSTAT1 alpha (NOT, LOW, MED, HIG, UNK) 61 3 Inlet PT Comments PRST1COM alpha (NYL, INA, B_P, UNK)
* All fields are comma separated, variable length.

-21-

Table 3 (continued)

Format of EPA I/M Lookup Table

Maximum

Field Length* Name Abbrev. Description

 62 4 Inlet PT Min. Pressure INLPRMIN numeric (nn.n in of H20, includes decima 63 4 Inlet PT Max. Pressure INLPRMAX numeric (nn.n in of H20, includes decima 64 3 EPA Purge Test Status PUSTAT alpha (NOT, LOW, MED, HIG, UNK) 65 3 EPA Purge Test PUSTCOM alpha (as needed)

 Comments

 66 3 Tracer Purge Test Status PUSTAT1 alpha (NOT, LOW, MED, HIG, UNK)  67 3 Tracer Purge Test PUST1COM alpha (BRP, UNK)

 Comments

 68 4 Tracer Purge Test TRCPUMIN numeric (nn.n in of H20, includes decima

 Minimum Pressure

 69 4 Tracer Purge Test TRCPUMAX numeric (nn.n in of H20, includes decima

 Maximum Pressure

 70 9 Date of Record RDATE alphanumeric (dd/MMM/yy) 71 1 Gas Cap Configuration GASCAP alphanumeric (A,B,C,E,F,G,H,L,O,Z,U,NTotal 271 (not including commas)

###
*

 Data for vehicles produced by small-volume manufacturers are not contained in the EPA certification

database, but are included in the certification data published annually in the Federal Register. As a result,

the information presented below for model years 1973–1978 also applies to all 1973–1993 models

produced by small-volume manufacturers. As noted previously, no 1994 and newer models produced by

small-volume manufacturers are included in the Lookup Table.

-22-

4. COMPUTATIONAL METHODOLOGIES

The majority of the vehicle parameter data contained in the I/M Lookup Table were either

imported directly from one of the EPA certification data sets or provided by the

manufacturers. However, it was necessary to compute or otherwise develop the values of

some vehicle parameters. Data sources are summarized in Table 4. More complete

descriptions of a selected number of the vehicle parameters, including the methods and

formulas used for the required computations, are presented below. For ease of reference,

each parameter is referenced by its respective field number in the vehicle parameter

database. The discussion is divided into two separate model-year categories (1979 and

newer, and 1973–1978), due to differences in the type of data available for each

category.* Unless otherwise noted, the information presented for 1979 and newer models

also applies to the older models as well.

1979 and Newer Vehicles

The sources of data for these vehicles are the EPA certification and fuel economy

databases that, prior to 1998, were located on the Wayne State computer system. These

data are now being maintained by EPA on its in-house Oracle database, CFEIS. 

Transmission Type (field #9) - The various transmission types contained in the

certification database were aggregated into three categories: manual, automatic, or either.

Vehicle Category Identification Number (field #10) - A unique code was developed and

assigned to each vehicle grouping that had identical entries in fields 1–9. This code

begins with the last two digits of the model year of vehicles included in each category,

followed by additional numbers assigned by Sierra. 

Fuel Type (field #11) - Almost all records contained in the Lookup Table are for gasolinepowered vehicles (fuel type =1). Beginning with the 1997 model year, a limited number

of alternatively fueled vehicle records are included, as follows:
-23-

Table 4

Data Sources for EPA I/M Lookup Table

Field Name Source of Data 1 Model Year Cert database (MDYR) 2 Manufacturer Code Code in SAE J2008, based on Cert database (M 3 Manufacturer Name Name in SAE J2008, based on Cert database (M 4 Manufacturer Division Developed by Sierra, based on Cert database 5 Public Model Name Developed by Sierra, based on Cert database (M 6 Body Style Unique code developed by Sierra 7 No. of Cylinders Cert database (#CYL), manufacturers 8 Engine Displacement Cert database (DISP), manufacturers 9 Transmission Type Cert database (developed from VTRN) 10 Vehicle Category ID Unique code developed by Sierra 11 Fuel Type Cert database (developed from FTYP), manufa 12 Evaporative System Type Cert database (EVSY), manufacturers 13 No. of Evap Canisters All-Data on-line database, manufacturers 14 Location of Canisters All-Data on-line database, manufacturers 15 Sales Class Cert database (SACL) 16 Equivalent Test Weight Cert database (ETW), manufacturers, other ind 17 Inertia Weight Class Computed from ETW 18 Track Road-Load hp at 50 mph (TRLHP) Computed from ETW and VCDT, manufactur 19 VIN Digit VIN decoding handbooks 20 VIN Characters VIN decoding handbooks 21 (Reserved) 22 Tire/Roll Interface Losses on Computed from DAXWT 8.625” Roll at 50 mph (GTRL8) 23 (Reserved) 24 (Reserved) 25 (Reserved) 26 Tire/Roll Interface Losses on Computed from DAXWT 20.0” Roll at 50 mph (GTRL20)
-24-

Table 4 (continued)

Data Sources for EPA I/M Lookup Table

Field Name Source of Data 27 (Reserved) 28 (Reserved) 29 (Reserved) 30 Total ASM5015 Horsepower EPA ASM horsepower equations 31 Total ASM2525 Horsepower EPA ASM horsepower equations 32 ASM5015 Horsepower for 8.625” Roll EPA ASM horsepower equations 33 ASM2525 Horsepower for 8.625” Roll EPA ASM horsepower equations 34 ASM5015 Horsepower for 20.0” Roll EPA ASM horsepower equations 35 ASM2525 Horsepower for 20.0” Roll EPA ASM horsepower equations 36 ASM5015 Tire/Roll Interface Losses EPA ASM horsepower equations on 8.625” Roll 37 ASM2525 Tire/Roll Interface Losses EPA ASM horsepower equations on 8.625” Roll 38 ASM5015 Tire/Roll Interface Losses EPA ASM horsepower equations on 20.0” Roll 39 ASM2525 Tire/Roll Interface Losses EPA ASM horsepower equations on 20.0” Roll 40 Average Drive Axle Wt. (DAXWT) Average of VAXF and VAXE in Cert database 41 Wheelbase Manufacturers (limited data) 42 Drive Layout Code Cert database (developed from DRCD), manuf 43 Full-time Four-Wheel-Drive? Manufacturers, Colorado DPHE 44 Location of Four-Wheel Selector Not currently entered 45 Main Fuel Tank Size Cert database (MTNK), manufacturers 46 Auxiliary Fuel Tank? Assumed=Y, if Cert database contains value fo 47 Auxiliary Fuel Tank Size Cert database (ATNK) 48 Traction Control? Manufacturers, Tier One, Colorado DPHE 49 Manual Traction Control Disablement Manufacturers, Colorado DPHE

 Possible?
-25-

Table 4 (continued)

Data Sources for EPA I/M Lookup Table

Field Name Source of Data 50 Location of Disablement Switch Manufacturers (limited data) 51 Anti-lock Braking? Manufacturers, Tier One 52 Anti-lock Braking Disablement Manufacturers

 Possible?

 53 2-Wheel-Drive Dyno Testing Sierra, from 4-wheel-drive and traction control 

 54 (Reserved) 55 (Reserved) 56 EPA Pressure Test Status Louisville I/M program 57 EPA PT Comments Manufacturers 58 EPA PT Min. Pressure No longer populated 59 EPA PT Max. Pressure No longer populated 60 Inlet Pressure Test Status Louisville I/M program 61 Inlet PT Comments Manufacturers 62 Inlet PT Min. Pressure No longer populated 63 Inlet PT Max. Pressure No longer populated 64 EPA Purge Test Status Not currently entered 65 EPA Purge Test Comments Not currently entered 66 Tracer Purge Test Status Not currently entered 67 Tracer Purge Test Comments Manufacturers 68 Tracer Purge Test Min. Pressure Manufacturers 69 Tracer Purge Test Max. Pressure Manufacturers 70 Date of Record Sierra 71 Gas Cap Configuration Stant Manufacturing
-26-

• Flexible-fuel vehicles (FFVs), with fuel type = 1; and

• Dedicated natural gas vehicles, with fuel type = 2. 

Equivalent Test Weight (field #16) - For 1994–1996 models, 300 lbs was added to the

curb weight data provided by EPA, and the resulting value rounded to the nearest 125-lb

increment, to compute equivalent test weight (ETW). In some cases, data provided

directly to Sierra by the manufacturers were used in place of the certification data.

Beginning with the 1997 model year records contained in the Lookup Table, the ETW

data incorporate changes in certification test weights specified in the Code of Federal

Regulations (CFR) for heavy light-duty trucks (LDTs). The issue of light-duty truck

definitions is relatively complicated, and confused by the fact that the definitions

contained in the CFR are not the same as those used in previous versions of EPA’s hightech test guidance. Table 5 is provided below to illustrate the differences between these

definitions. 

Table 5

Light-Duty Truck Definitions

Ref. Category Weight Range

CFR

Light LDT: 0–6,000 lbs GVWR

 LDT1 Light LDT under 3,751 lbs LVWa

 LDT2 Light LDT of 3,751–5,750 lbs LVW

Heavy LDT: 6,001–8,500 lbs GVWR

 LDT3 heavy LDT of 3,751–5,750 TWb

 LDT4 heavy LDT greater than 5,750 TW

High-Tech

Guidance

(June 1996)

LDT1 0–6,000 lbs GVWR

LDT2 6,000–8,500 lbs GVWR

High-Tech

Guidance

(April 2000)

LDT (0–6,000 lbs GVWR)

LDT (6,001–8,500 lbs GVWR)

a

LVW = curb weight + 300 lbs, which is equivalent to the equivalent test weight (ETW) values

contained in the EPA I/M Lookup Table for most vehicles. The ETW values are basically rounded

versions of the test weight basis (see next footnote) for each vehicle.

b

TW = total weight. TW is equivalent to LVW for all vehicles except MY1994 and later Tier 1

heavy LDTs (e.g., those certified to the Tier 1 standards). For MY1994 and later Tier 1 heavy

LDTs, ALVW is to be used for TW. ALVW is defined as (curb weight + GVWR) / 2.
-27-

The definitions noted in the table for the June 1996 version of EPA’s high-tech guidance

are consistent with those contained in EPA’s MOBILE models, but clearly conflict with

the CFR definitions. The August 1998 and later versions of the guidance address this

issue somewhat by eliminating the 1 and 2 after the LDT titles in the standards tables. 

According to CFR §86.129-94, test weights for model year 1994 and later heavy LDTs

certified to Tier 1 standards are to be based on adjusted loaded vehicle weight (ALVW). 

ALVW is defined as the average of curb weight plus gross vehicle weight rating (i.e.,

[curb weight + GVWR] / 2) in CFR section 86.094-2. EPA also inserted ALVW in place

of LVW for the 5,750 lb breakpoint in the standards in the August 1998 guidance and

indicated this breakpoint is to be used for 1996 and newer vehicles. (The June 1996

version indicated it should be used for 1994+ Tier 1 LDTs.) This is because Tier 1

vehicles were phased in beginning with the 1994 model year, with 1996 being the first

model year with all vehicles certified to Tier 1 standards. EPA’s revision to include the

1996 model year as the first year for the 5,750 lb breakpoint eliminates the need for

inspectors to determine whether a 1994–1995 vehicle was certified to the Tier 1

standards, in order to set the appropriate IM240 cutpoints.

The effect of the above requirement is that the proper IM240 test weight for 1996 and

newer heavy LDTs is the average of curb weight plus GVWR. However, it appears that

the 1996 model year certification data provided to Sierra for inclusion in the Lookup

Table did not include ALVW values. A review of ETW values for the 1996 LDTs

included in the table shows few in the 5,500 lbs or greater range. The reason for this

oversight is unclear, but may be related to the transition to the CFEIS system that

occurred at about this same time period. Conversely, a review of 1997 model year and

later data contained in the Lookup Table shows a number of LDTs with heavier ETWs

(up to as much as 8,000 lbs), which clearly reflect the correct use of ALVW. 

The significance of this issue is that to properly test all of the 1997 models included in the

table, IM240 programs will either need to have dynamometers that have the capability of

handling inertia weight settings of up to as much as 8,500 lbs, or simply underload the

vehicles relative to how they were initially certified. 

Inertia Weight Class (field #17) - These data are computed from the ETW values

contained in the certification database or provided by the manufacturers, using the

approach incorporated into the conversion table contained in CFR §86.129-94. Under

this method, all ETW values are rounded down to the nearest inertia weight class. Thus,

for example, vehicles with ETWs of 3000 and 3250 lbs would both be considered to have

the same inertia weight class of 3000 lbs. For the lighter vehicles (i.e., those with ETWs

less than 3000 lbs), the CFR table includes inertia weight classes in increments of

250 lbs. For ETWs of greater than 3000 lbs, the CFR inertia weight classes are based on

increments of 500 lbs. The same approach is used to compute the inertia weight classes

in the Lookup Table, with all ETWs above 3000 lbs being rounded down to the nearest

500-lb inertia weight class, and all ETWs below 3000 lbs rounded down to the nearest

250-lb inertia weight class. 
*

Unless otherwise noted, all references to the high-tech test procedures contained in this section refer to the

June 1996 version of the guidance. 

-28-

Track Road-Load Horsepower (field #18) - These data are computed from the ETW and

VCDT values contained in the certification database, using the formula contained in

§85.2226(a)(2)(iv) of the high-tech I/M test procedures.* This formula is as follows:

TRLHP = (0.5*ETW/32.2) * (V1

2

-V2

2

)

 (550*ET)

where: ET = vehicle coastdown time (VCDT) from 55 to 45 mph

ETW = equivalent test weight (lbs)

V1 = initial velocity in ft/sec equivalent to 55 mph

V2 = final velocity in ft/sec equivalent to 45 mph

As discussed previously, VCDT data were not available for a large portion of the

1979-1980 models contained in the Wayne State databases. For these models, an

alternate method of computing TRLHP values must be used. TRLHP settings for these

models, based on vehicle type and either inertia weight class or number of cylinders, are

selected using the revised IM240 and ASM default values (dated June 7, 1995, and

July 6, 1995, respectively) provided by EPA. For vehicles with inertia weights heavier

than shown in the revised default table, TRLHP values corresponding to the heaviest test

weight for the appropriate vehicle category were used.

In some cases, data provided directly to Sierra by the manufacturers were used in place of

the certification data or default values.

VIN Digit and VIN Characters (fields #19 and 20) - The respective EPA guidance

documents for IM240 and ASM testing contain separate sets of recommended cutpoints

for light trucks with a gross vehicle weight rating (GVWR) of (1) 0–6000 pounds; and 

(2) 6001–8500 pounds. As a result, GVWR information is needed for these vehicles in

order to determine the correct emissions standards to which they should be tested. 

Version 1.7.2 and subsequent versions of the Lookup Table have therefore been modified

to aid I/M programs in determining the GVWR for a particular vehicle. 

To accomplish this, Fields 19 and 20 have been defined as VINPLC and VINCHAR. 

(These fields were reserved in the previous version of the Lookup Table.) These fields

are populated for 1981 and later makes of light-duty trucks (LDTs) that include models

both under and over 6000 lbs GVWR. Certain pre-1981 records are also populated, if

available VIN decoding information indicates that 1981+ VIN standardization rules also

apply to these vehicles. Data included in the two fields are as follows:

1. VINPLC indicates the location of the VIN digit that identifies the GVWR range

of the vehicle; and
-29-

2. VINCHAR includes all VIN characters that represent LDTs with GVWRs of

less than or equal to 6000 pounds.

As an example of the available information, GVWR range is indicated by the fourth VIN

digit on 1994–95 Ford LDTs, based on the following codes:

• A = Under 3000 lbs • G = 8001–8500 lbs

• B = 3001–4000 lbs • H = 8501–9000 lbs

• C = 4001–5000 lbs • J = 9001–10000 lbs

• D = 5001–6000 lbs • 3 = 10001–14000 lbs

• E = 6001–7000 lbs • 4 = 14001–16000 lbs

• F = 7001–8000 lbs

In this example, VINPLC would be populated with a “4” and VINCHAR would contain

the following entry: “ABCD.” The combination of these entries indicates that a 1994–95

Ford LDT that has an A, B, C, or D in the fourth VIN digit will have a GVWR of less

than or equal to 6000 pounds. Users can thus use this information and the VIN entry to

determine whether a particular 1994–95 Ford LDT should be subject to 0–6000 or

6001–8500 pound tailpipe standards. 

Generic Tire/Roll Interface Losses on 8.625” Roll (field #22) - These data are computed

from the full and empty drive axle weights (VAXF and VAXE) contained in the Cert

database, using the formula contained in §85.2226(a)(2)(xv) of the high-tech I/M test

procedures and assuming that average drive axle weight (DAXWT) equals

(VAXF+VAXE)/2. The formula is as follows:

GTRL@ 50 mph-8 = (-0.378193) + [(0.0033207) * (DAXWT)]

Generic Tire/Roll Interface Losses on 20.0” Roll (field #26) - These data are computed

from the full and empty drive axle weights (VAXF and VAXE) contained in the

certification database, using the formula contained in §85.2226(a)(2)(xvi) of the high-tech

I/M test procedures and assuming that average drive axle weight (DAXWT) equals

(VAXF+VAXE)/2. The formula is as follows:

GTRL@ 50 mph-20 = (0.241645) + [(0.0020844) * (DAXWT)]

Total ASM5015 Horsepower (field #30) - These data are computed from the following

ASM horsepower equations provided by EPA and the At8, Bt8 and Ct8 default values

provided in §85.2226(a)(2)(xiii):

THP5015 = HP50158 + GTRL@ 15 mph-8
*

 This equation is contained in SAE Paper No. 891120.

-30-

HP50158 = ETW/250*

GTRL@ 15 mph-8 = {[At8*(15 mph)] + [Bt8*(15 mph)2] + [Ct8*(15 mph)3]} * 

 GTRL@ 50 mph-8

where: At8 = 0.76 / 50

Bt8 = 0.33 / 2,500

Ct8 = - 0.09 / 125,000

Total ASM2525 Horsepower (field #31) - These data are computed from the following

ASM horsepower equations provided by EPA and the At8, Bt8, and Ct8 default values

provided above:

THP2525 = HP25258 + GTRL@ 25 mph-8

HP25258 = ETW/300*

GTRL@ 25 mph-8 = {[At8*(25 mph)] + [Bt8*(25 mph)2] + [Ct8*(25 mph)3]} * 

 GTRL@ 50 mph-8

ASM5015 Horsepower for 8.625” Roll (field #32) - These data are based on the

following equation, which is presented in SAE Paper No. 891120:

HP50158 = ETW/250

ASM2525 Horsepower for 8.625” Roll (field #33) - These data are based on the

following equation, which is presented in SAE Paper No. 891120:

HP25258 = ETW/300

ASM5015 Horsepower for 20.0” Roll (field #34) - These data are computed from the

following ASM horsepower equations provided by EPA and the At20, Bt20, and Ct20

default values provided in §85.2226(a)(2)(xiii):

HP501520 = THP5015 - GTRL@ 15 mph-20

GTRL@ 15 mph-20 = {[At20*(15 mph)] + [Bt20*(15 mph)2]+ [Ct20*(15 mph)3]} * 

 GTRL@ 50 mph-20

where: At20 = 0.65 / 50

Bt20 = 0.48 / 2,500
-31-

Ct20 = - 0.13 / 125,000

ASM2525 Horsepower for 20.0” Roll (field #35) - These data are computed from the

following ASM horsepower equations provided by EPA and the At20, Bt20, and Ct20

default values provided above:

HP252520 = THP2525 - GTRL@ 25 mph-20

GTRL@ 25 mph-20 = {[At20*(25 mph)] + [Bt20*(25 mph)2] + [Ct20*(25 mph)3]} * 

 GTRL@ 50 mph-20

ASM5015 Tire/Roll Interface Losses on 8.625” Roll (field #36) - These data are

computed from the following ASM horsepower equation provided by EPA and the At8,

Bt8, and Ct8 default values provided above:

GTRL@ 15 mph-8 = {[At8*(15 mph)] + [Bt8*(15 mph)2] + [Ct8*(15 mph)3]} * 

 GTRL@ 50 mph-8

ASM2525 Tire/Roll Interface Losses on 8.625” Roll (field #37) - These data are

computed from the following ASM horsepower equation provided by EPA and the At8,

Bt8, and Ct8 default values provided above:

GTRL@ 25 mph-8 = {[At8*(25 mph)] + [Bt8*(25 mph)2] + [Ct8*(25 mph)3]} * 

 GTRL@ 50 mph-8

ASM5015 Tire/Roll Interface Losses on 20.0” Roll (field #38) - These data are computed

from the following ASM horsepower equation provided by EPA and the At20, Bt20, and

Ct20 default values provided above:

GTRL@ 15 mph-20 = {[At20*(15 mph)] + [Bt20*(15 mph)2]+ [Ct20*(15 mph)3]} * 

 GTRL@ 50 mph-20

ASM2525 Tire/Roll Interface Losses on 20.0” Roll (field #39) - These data are computed

from the following ASM horsepower equation provided by EPA and the At20, Bt20, and

Ct20 default values provided in above:

GTRL@ 25 mph-20 = {[At20*(25 mph)] + [Bt20*(25 mph)2] + [Ct20*(25 mph)3]} * 

 GTRL@ 50 mph-20

Average Drive Axle Weight (field #40) - These data are computed from the full and

empty drive axle weights (VAXF and VAXE) contained in the certification database,
-32-

assuming that DAXWT = (VAXF+VAXE)/2. In some cases, when no value of VAXE is

provided in the Certification database, the DAXWT is calculated as 60% of ETW for

front-wheel-drive sedans and station wagons, and 50% of ETW for all other vehicle

types.

Wheelbase (field #41) - These data are available in non-electronic form in the annual

Automotive News Market Data Books for each model year. In addition, the All

Wheel/Traction Control Guide compiled by the Colorado Department of Public Health

and Environment (CDPHE) also contains wheelbase data. Only limited wheelbase data

provided by the manufacturers (e.g., Ford) have been input to the I/M Lookup Table.

Drive Layout Code (field #42) - The various drive code types contained in the

certification database have been aggregated into three categories: front, rear, or fourwheel. It is impossible to tell from the certification data whether a vehicle has selectable

or full-time four-wheel-drive. Because of this, the manufacturers were asked to identify

which vehicles had full-time four-wheel drive. These data were used to disaggregate

vehicles equipped with four-wheel-drive into selectable or full-time four-wheel-drive

categories.

Full-Time Four-Wheel-Drive (field #43) - As discussed above, data from the

manufacturers were used to identify which vehicles had full-time four-wheel-drive. Data

from the CDPHE All Wheel/Traction Control Guide were also input, where appropriate,

in cases of missing manufacturer data.

Location of Four-Wheel Selector (field #44) - Due to time and resource constraints, these

data have not been input to the Lookup Table.

Auxiliary Fuel Tank (Yes/No) (field #46) - A “yes” answer is assumed for this entry if the

certification database contains a value for the auxiliary fuel tank size; otherwise, this

entry is assumed to be “no.”

Location of Traction Control Disablement Switch (field #50) - Only limited data provided

by the manufacturers (e.g., Volkswagen) have been input to the Lookup Table. As

described in more detail in Section 5, the location codes used in this field are identical to

those proposed for use in mapping the location of OBDII diagnostic link connectors.

EPA Pressure Test Status and Comments (fields #56-57) - These data are based on

pressure testability data obtained from the Louisville I/M program and reasons for

untestability received from selected manufacturers. 

Minimum and Maximum Pressures for EPA Pressure Test (fields #58-59) - These fields

have been left blank starting with Version 1.8.2 of the Lookup Table. 

Inlet Pressure Test Status and Comments (fields #60-61) - These data are based on

pressure testability data obtained from the Louisville I/M program and reasons for

untestability received from selected manufacturers. 
*

According to Stant, an upgraded black adapter has been developed to address problems that users have

experienced in attempting to test certain Honda models because the fuel fillpipes on these vehicles are

slightly different from SAE specifications. The upgraded adapter can be visually distinguished from the

previous unit based on the presence of a white “gripping ring.” Stant intends to continue to use the color

black to describe the upgraded version of this adapter. Since this is how it is coded in the I/M Lookup

Table, no change will be made to the table entries in response to the upgrade. 

-33-

Minimum and Maximum Pressures for Inlet Pressure Test (fields #62-63) - These fields

have been left blank starting with Version 1.8.2 of the Lookup Table. 

Tracer Purge Comments (field #67) - These data are based on reasons for untestability

received from selected manufacturers. 

Minimum and Maximum Pressures for Tracer Purge Test (fields #68-69) - These data are

based on data received from selected manufacturers. 

Gas Cap Configuration (field #71) - To facilitate gas cap pressure testing, this field

identifies the gas cap adapter type that should be used for testing the vehicle, based on

data received from Stant Manufacturing. A description of the field is provided below.

Field Entry Stant Adapter Descriptor

A Blue

B Yellow

C Red

E Green

F Black*

G Gray

H Threaded

L Light Blue (new)

O Orange (new)

Z Varies

U Untestable

N Unknown or no adapter required 

Pre-1979 Model Year Vehicles

The database descriptions, data sources, and computational methodologies presented

above primarily apply to those model years contained in the EPA certification and fuel

economy data provided directly to Sierra by EPA, i.e., for model year 1979 and later. In

addition to those data, Sierra also obtained certification data for the 1979–1993 model

years that were published annually in the Federal Register. These data were similar, but

not identical, to the certification data provided by EPA. (The Federal Register data

included some models that were not included in the EPA databases.) Federal Register

data for model years 1973–1978 were also entered manually. As described previously,

fewer data are available for these earlier model years. Accordingly, the following
-34-

methodologies were used to develop the necessary vehicle test parameters (dynamometer

settings) for those models for which only Federal Register certification data are available

(i.e., 1972–1978 models plus some later model vehicles).

Number of Cylinders (field #5) - These values are not included in the Federal Register

database; therefore, this field has been left blank for pre-1979 vehicles for which no data

have been provided by the manufacturers or obtained from other sources. 

Equivalent Test Weight (field #18) - These values are included in the Federal Register

database only for 1980 and later models; therefore, this field has been left blank for pre1980 vehicles for which no data have been obtained from independent sources (e.g., the

Automotive News Market Data Book) or provided by the manufacturers. 

Inertia Weight Class (field #19) - Inertia weight class (IWC) data were included in the

Federal Register data set for 1979 and earlier models. These values, rounded down to the

nearest 500-lb weight class for IWC values above 3000 lbs and down to the nearest

250-lb weight class for IWC values below 3000 lbs, were used unless better data (e.g.,

from the manufacturers) were available. For 1980 and later models, inertia weight classes

were computed by rounding ETW values in the same manner.

Track Road-Load Horsepower (field #20) - TRLHP settings for IM240 testing were based

on the model-year-specific default values developed by Sierra using the approach

described in Section 2. In some cases, data provided directly to Sierra by the

manufacturers were used in place of the default values.

Average Drive Axle Weight (field #32) - As described above, DAXWT data are needed

to compute GTRL values. Because these data were not published in the Federal Register,

the GTRL values in EPA’s revised default table were assumed. The DAXWT values for

pre-1979 vehicles were calculated as 60% of ETW for front-wheel-drive sedans and

station wagons, and 50% of ETW for all remaining vehicle types.

###
-35-

5. LOOKUP TABLE UPDATES

Additional modifications, based on comments received on the previous version of the

Lookup Table, were incorporated into Version 1.8.4 of the table. These changes are listed

below.

1999 Models

1999 model year vehicles, based on manufacturer fuel economy and vehicle certification

data, data submitted by the vehicle manufacturers, and other sources, have been added to

the table. A limited number of models (particularly those manufactured by small-volume

manufacturers) may be missing. Users are encouraged to contact Sierra or EPA directly if

they identify missing models.

Data Parameters - For the 1999 models included in the table, complete dynamometer

loadings and testability parameters have been included. Stant gas cap adapter information

was also added based on a review of the listings contained in the Stant manual. 

Default Values - 1999 model-year-specific default values have been included at the

beginning of the records for this model year. 

Evaporative Fuel Inlet Pressure Test Data

Data regarding alternative test pressures for use in conducting the fuel inlet vehicle

evaporative control system integrity (pressure) test that were provided in previous

versions of the table have been deleted due to (1) concerns that some of the test pressures

were sufficiently high to create the potential for damaging evap systems; (2) the

infeasibility of identifying suitable test pressures for 1996-1999 model year vehicles due

to the phase-in of vehicles equipped with enhanced evaporative emission control systems

into the in-use fleet; and (3) the fact that no programs have been using the alternative test

pressures. It is recommended that anyone wishing to conduct vehicle pressure testing

follow EPA guidance and use the standard test pressure specified contained therein.
-36-

Other Modifications

Miscellaneous Changes - Information provided by the Virginia Department of

Environmental Quality was used to investigate differences between test data recorded in

its I/M program and information contained in the table. Based on the results of this

review, miscellaneous changes were made related to transmission type, engine

displacement, and division and model names. 

Updated information provided by Honda, Mitsubishi, Subaru, Isuzu, and Land Rover

regarding previously existing records was incorporated.

An extensive review was performed of existing records in the table. This resulted in

corrections to (1) TRLHP settings for a few 1994-1995 models; (2) drive layout code

entries for a number of 1978-1998 models (most related to four-wheel-drive options); and

(3) gas cap entries for some 1990-1991 Hondas. In addition, it was noted that a number

of 1997-1998 models included in the table had exceptionally high test weights and

TRLHP. These models appear to be heavy-duty vehicles and should not be included in

the table (which is supposed to contain information on only passenger cars and light-duty

trucks). They were therefore deleted. 

Record Date - The date on each record that was either added or modified as a result of the

above changes reflects the release date of Version 1.8.4 of the Lookup Table. 

###