# Evaluation of the

Effectiveness of On-Board

Diagnostic (OBD) Systems in

Identifying Fuel Vapor Losses

from Light-Duty Vehicles

FINAL REPORT

Version 11

Contract No. EP-C-06-0-80

Work Assignment 5-10

Prepared by:

Eastern Research Group, Inc.

Prepared for:

U.S. Environmental Protection Agency

Revised by:

Eastern Research Group, Inc. and

U.S. Environmental Protection Agency in response to

External Peer Review comments provided in RTI

Technical Memo entitled “ Peer Review of LDV/ LDT

OBD and High Evaporative Emission Report, Work

Assignment 4-01, (RTI 005) ”, May 2012



## April 5, 2013

### ERG No.: 0218.05.010.001



## Evaluation of the Effectiveness of On-Board Diagnostic (OBD ) Systems in

Identifying Fuel Vapor Losses from Light-Duty Vehicles

FINAL REPORT

Version 11

Contract No. EP-C-06-0-80

Work Assignment 5-10

Prepared by:

Eastern Research Group, Inc.

3508 Far West Blvd, Suite 210

Austin, TX 78731

Prepared for:

Ms. Connie Hart

OTAQ Emissions Program Group

U.S. Environmental Protection Agency

2000 Traverwood Dr.

Ann Arbor MI 48105

April 5, 2013

### i Table of Contents

1.0 I NTRODUCTION



### .................................................. ................................................... ........ 1-1

2.0 B ACKGROUND



### .................................................. ................................................... ......... 2-1

2.1 OBD Overview .......................................

................................................... ...... 2-1

2.2 OBD Monitors and Readiness .......................... ................................................ 2-2

2.3 OBD DTCs ..........................................

................................................... ......... 2-3

2.4 Evaporative Emissions Control System Overview ......... ................................... 2-4

2.5 Recent Evaporative Emissions Real World Test Programs . .............................. 2-5

3.0 A NALYSIS



### .................................................. ................................................... ............... 3-1

3.1 Data Preparation ....................................

................................................... ....... 3-2

3.2 Data Analysis Results .............................

................................................... ...... 3-2

3.3 Comparison of SHED Values to Presence of OBD Evaporati ve System

DTCs ..............................................

................................................... .............. 3-3

4.0 C ONCLUSIONS



### .................................................. ................................................... ......... 4-1

List of Tables

T ABLE 

### 1-1. O VERVIEW OF 

### D ATASETS USED IN 

### A NALYSIS



### .................................................. ....... 1-2

T ABLE 

### 3-1. S UMMARY OF 

### M ATCHED 

### SHED AND 

### I/M R ECORDS USED IN 

### A NALYSIS 

### .................. 3-2

T ABLE 

### 3-2. P AIR 

### C OUNTS FOR 

### MY96 L IPAN



### , K EN 

### C ARYL



### , AND 

### D ENVER 

### H IGH 

### E VAP



### S TUDY 

### P ARTICIPANTS 

### C OMBINED



### .................................................. ............................... 3-3

T ABLE 

### 3-3. N UMBER OF 

### P AIRS WITH 

### E VAP 

### DTC S 

### S ET 

### V ERSUS 

### H IGH AND 

### L OW 

### SHED S 

### (1.0

G 

### /Q HR CUTPOINT 

### )..................................................

................................................... .... 3-4

T ABLE 

### 3-4. N UMBER OF 

### P AIRS WITH 

### E VAP 

### DTC S 

### S ET 

### V ERSUS 

### H IGH AND 

### L OW 

### SHED S 

### (0.3

G 

### /Q HR CUTPOINT 

### )..................................................

................................................... .... 3-4

T ABLE 

### 3-5. D ETAILS FOR 

### V EHICLES WITH 

### SHED R ESULTS 

### > 1 G 

### /Q HR 

### ( EXCLUDING LIQUID

AND UNMONITORED VAPOR LEAKS 

### ) ................................................. .............................. 3-6

T ABLE 

### 3-6. M ODEL YEAR 

### C OUNTS FOR 

### H IGH AND 

### L OW 

### SHED P AIRS IN THE 

### D ATA 

### .................. 3-9

T ABLE 

### 4-1. C OMPARISON OF 

### SHED AND 

### OBD R ESULTS FOR 

### V EHICLES WITH 

### SHED

E MISSIONS 

### > 1 G



### /Q HR 

### (S UMMARY OF 

### I NFORMATION FOR 

### V EHICLES 

### L ISTED IN



### T ABLE 

### 3-5) ................................................

................................................... ............... 4-2

### ii List of Figures

Figure 1-1. Electronic HC detector used for MCM Inspections ............................................... 1-2

Figure 1-2. Portable Sealed Housing for Evaporative Determi nation (PSHED) used in

Denver High Evaporative Emission Field Studies ......... ............................................... 1-3

### 1-1



## 1.0 Introduction

This document is Eastern Research Group’s (ERG’s) final r eport on evaluating the

effectiveness of Second Generation On-Board Diagnostic (OBD) systems through a comparative

analysis of evaporative emissions field data collected i n the Denver area during the past four

years. These field studies were performed through Cooperat ive Research and Development

Agreements (CRADAs 471-08 and 471-A-11) between the Assessment and Standards Division

(ASD) within the Office of Transportation and Air Qualit y (OTAQ) of the United States

Environmental Protection Agency (EPA) and the Colorado Depa rtment of Public Health and

Environment (CDPHE), with support provided by ERG under Work Ass ignments 1-2, 2-2, 2-4,

3-4 and 4-4 of Contract EP-C-06-080 with the EPA. A wealth of data has been collected at the

Denver Lipan 1 

### and Ken Caryl 2 

### Inspection and Maintenance (I/M) lanes using a Portable Se aled

Housing for Evaporative Determination (PSHED) and remote sensing devices. Because the

studies took place at I/M lanes in Colorado, OBD informat ion is also available for each vehicle.

CDPHE independently performed additional work during the sum mer of 2010 in a repair

effectiveness study conducted at CDPHE’s Aurora and West Tech test centers. During this

“Denver 2010” study, vehicles were recruited and brought to one of the two CDPHE facilities

where laboratory-grade Sealed Housing for Evaporative Det ermination (SHED) testing was

performed, in addition to other evaporative control system diagnostic tests. Repairs were

performed on vehicles with elevated evaporative emission levels. Repeat tests were conducted to

assess the effectiveness of the evaporative emissions repairs performed by CDPHE.

The focus of this report is on the analysis of evaporat ive emissions and related data

collected on model year 1996 and newer light-duty vehicles e quipped with OBD systems.

Results for the Lipan, Ken Caryl and Denver 2010 studies are analyzed in this report, and Table

1-1 lists the number of 1996 and later OBD equipped vehicles w hich participated in each of the

three studies.

1 DeFries, T; Lindner, J; Kishan, S; Palacios, C (2011) “ Investigation of Techniques for High Evaporative

Emissions Vehicle Detection: Denver Summer 2008 Pilot S tudy at Lipan Street Station”

2 DeFries, T; Palacios, C; Kishan, S (2012) “Estimated Summ er Hot Soak Distributions for the Denver’s Ken Caryl

IM Station Fleet ”

### 1-2 Table 1

- 1 . Overview of Datasets used in Analysis

Dataset Source Number of 1996+

Vehicles Data Available in Dataset

Lipan Participant (LP) 24 OBD , MCM * , PSHED **

Ken Caryl Participant (CP) 89 OBD , MCM, PSHED

Denver 2010 Participant (DP) 68 OBD , MCM, PSHED or LSHED

Total participants (vehicles) in 3 studies 181 OBD

, MCM, PSHED or LSHED



### *MCM- Modified California Method

**PSHED – Portable Sealed Housing for Evaporative Determinat ion

The purpose of this analysis is to evaluate OBD’s ability to identify vehicles with

elevated evaporative emissions (due to a leak in the fuel/v apor control system). OBD systems

are not designed for and are generally not capable of determi ning and setting a code for a leak in

the fuel system which would result in a liquid leak. 3 

### Three types of data are used in the analysis

in this report:

OBD – OBD codes which indicate system or component malfun ctions that could result in

elevated exhaust or evaporative emission levels. During ro utine I/M inspections, vehicle OBD

system data (including diagnostic trouble codes (DTCs)) is collected for 1996 and newer

vehicles.

MCM – Vehicles in all three studies received a Modified Calif ornia Method (MCM)

inspection, which is an under-hood and under-body inspection for evaporative emissions using

olfactory, visual, and electronic hydrocarbon (HC) detector checks. MCM variables are generally

discrete. MCM inspections provide several kinds of informat ion including smell/no-smell noted

by the inspector, visual condition of various fuel system and evaporative emissions control

system components, and detect/no-detect by the electronic HC detector (shown in Figure 1-1).

Figure 1-1. Electronic HC detector used for MCM In spections

3 40 CFR 86.099-17

### 1-3

PSHED and LSHED – Hot-soak evaporative emission estimates were gathered f or each

vehicle in the three studies by placing the vehicle in a L aboratory Sealed Housing for

Evaporative Determination (LSHED) or a Portable Sealed Ho using for Evaporative

Determination (PSHED). LSHED values are reported as con tinuous variables with units of

grams HC/15minutes. In the Lipan and Ken Caryl studies, a PSHED was used, while in the

Denver 2010 study a PSHED was used for the vehicles tested at the CDPHE’s West Tech

Center, and a laboratory (conventional) SHED was used fo r vehicles tested at CDPHE’s Aurora

laboratory testing facility. Performance of the PSHE D has been evaluated in comparison to a

laboratory SHED in a separate report 4 

### which shows that for fifteen minutes the PSHED had an

average Recovery of 97.6% and an average Retention of 95.7%, which are within the

requirements of the laboratory SHED for this time peri od. Figure 1-2 shows the PSHED used in

the Denver studies.

Figure 1-2. Portable Sealed Housing for Evaporativ e Determination (PSHED) used

in Denver High Evaporative Emission Field Studies

The analysis in this report is broken out by vehicle model year, OBD evaporative system

readiness monitor status, and the presence of enhanced ev aporative emission controls for 1996-

1998 vehicles. Vehicles with “Not Ready” systems (as desc ribed in Section 2.0, Background)

4 Lindner, J; DeFries, T (2012) “Evaluation of Portable SHED Characteristics”

### 1-4

associated with the relevant OBD code categories are de lineated in the analysis. The break-outs

were made to the finest level of detail possible; howev er, this was dependent on the sample size

for each category. OTAQ assisted ERG in identifying those 1996-1998 vehicles that were

equipped with enhanced-evaporative emissions systems, as wel l as whether a vehicle was

certified to meet the federal or California emission st andards. 5

5 Note that US EPA enhanced evaporative emission contro ls for passenger cars and light trucks phased in over the

1996-1999 model years.

### 2-1



## 2.0 Background

2.1 OBD Overview

Second-Generation Onboard Diagnostics (OBDII, typicall y referred to simply as OBD) is

a system used to monitor the status and performance of a v ehicle’s powertrain and emissions

control system components in order to detect malfunction s which could result in an emissions

increase above a specified threshold. For tailpipe emiss ions, this threshold is 1.5 times the

federal certification emission standard. 6 

### For evaporative emissions control systems, the OBD

system monitors for proper operation of components, adequate purge flow of the evaporative

control system and vapor leaks equivalent to certain ori fice diameters (such as 0.020” or 0.040”,

depending on which of the applicable OBD standards were foll owed for certification). All

model year 1996 and newer light-duty non-diesel on-road vehi cles sold in the United States are

federally required to be equipped with OBD. 7



### The OBD system consists of the powertrain control modu le (PCM), various engine and

transmission input sensors and components, emission cont rol components, a malfunction

indicator light (MIL) and a diagnostic link connector (DL C). These systems work together to

monitor a vehicle’s powertrain and emission control com ponents during vehicle operation and to

store diagnostic information and alert the driver if a malfunction is identified. Although the

emission standards to which OBD must comply are federall y defined, development of the

systems and algorithms used to identify malfunctions is th e responsibility of each vehicle

manufacturer. Therefore, monitoring criteria and the a mount of time required for a monitor to

achieve readiness (as defined in the next section) can v ary among vehicle manufacturers and

even vehicle models and model years. In addition, some manufacturers choose to comply with

more strict standards than federal standards in order t o ensure all their vehicles are 50-state legal.

For example, many manufacturers choose to have their O BD systems certified to detection of a

0.020” diameter vapor leak required by the California Air Reso urces Board rather than the less

strict federal 0.040” requirement in order to maintain mode l consistency and avoid the 49-state

certification issue.

Diagnostic information is stored in the system using a f ive digit code which provides

information about the source of the malfunction, and t he driver is alerted when the MIL

(commonly referred to as a check engine light) is illumi nated. By connecting an OBD scan tool

(or an inspection and maintenance analyzer) to the vehicle’ s DLC, certain information including

6 Center for Automotive Science & Technology at Weber State University. (2000). On-Board Diagnostics

Conference 2000 On-Board Diagnostics Manual. (pp. 2-5). Ogde n, Utah: Weber State University.

7 40 CFR 86.094-17

### 2-2

the vehicle’s MIL command status (whether the MIL is c ommanded on or off) and any stored

diagnostic trouble codes (DTCs) can be downloaded from th e vehicle’s PCM. These DTCs are

five-digit alpha numeric codes of the format P####. The codes of primary interest in this report

are the generic (set in federal regulations) P0 series codes (i.e., P0###) defined in SAE J1979,

since these are common among all vehicle manufacturers a nd are the codes primarily used in

vehicle inspection and maintenance programs.

2.2 OBD Monitors and Readiness

Before a vehicle’s OBD system can make a determination about whether or not

malfunctions are occurring, a series of tests are req uired to evaluate the operational status of the

various OBD subsystems. These operational tests are c ategorized into meaningful sets of

subsystems referred to as monitors. Each monitor has a r eadiness code that identifies whether or

not the related subsystem has been evaluated. If a monito r is “ready”, that simply means that

testing on that particular subsystem has been completed, and results are available (a DTC will be

stored if a malfunction was identified). On the other hand, if a monitor is “not ready”, testing of

that particular subsystem has not been completed, so no information is yet available on whether

or not malfunctions exist in that subsystem. Therefore , a lack of DTCs for a “not ready” monitor

does not indicate that no malfunctions (i.e., DTCs) ar e present; it simply means the system

evaluation is not complete.

Monitors may be classified as those that are always “re ady” (continuous monitors), and

those that become ready at different times (non-conti nuous monitors). The three continuous

monitors include the Comprehensive Component, Misfire and Fuel System monitors, while the

typical non-continuous monitors are the Oxygen Sensor, Ca talyst, Exhaust Gas Recirculation

(EGR), Evaporative Emissions Control System (evaporativ e system), Air Injection System

(AIR), Thermostat and Positive Crankcase Ventilation System (PCV) monitors. 8 

### As the name

implies, the continuous monitors are always running (these are “critical” monitors which

primarily protect the catalytic converter). The non-co ntinuous monitors are only evaluated under

certain powertrain operating conditions (the vehicle’s PCM uses complex algorithms to

determine when these non-continuous monitors may be run). For this reason, at any point in

time, a vehicle will have a number of “ready” monitors , and also may have a number of “not

ready” monitors. Normally, non-continuous monitors whic h are “not ready” are set to assess

readiness after each key-on operating event.

8 Birnbaum, R, & Truglia, J (2000). Getting to Know OBDII . asttraining.com, ISBN 0-9706711-0-5, pg, 32.

### 2-3

The amount of time necessary for monitors to achieve re adiness varies on a number of

factors. OBD systems on older model-year vehicles (i. e., model year 1996-2000 vehicles)

typically take longer to achieve “readiness” than newer vehicles (as monitoring algorithms have

been refined and improved over the years). In addition, d ifferent types of systems require

different conditions (referred to as enabling criteria) b efore they can be tested. For example, the

operating conditions required to test an oxygen sensor are more frequently encountered than the

operating conditions necessary to evaluate the evaporativ e system monitor (the enabling criteria

are met more frequently for an oxygen sensor monitor tha n for an evaporative system monitor).

Therefore, after a PCM reset, the oxygen sensor monitor status is usually “ready” before the

evaporative system monitor status is “ready”, and conse quently, more vehicles on the road likely

have “ready” oxygen sensor monitors than vehicles with “r eady” evaporative system monitors.

Once a monitor’s system evaluation has been completed , the status changes from “not ready” to

“ready”, and at that time, if any malfunctions are dete cted, a DTC is stored. However, until the

monitor is “ready”, no information can be known about whether or not malfunctions are present.

This assessment cannot be made until the monitor is “re ady”.

2.3 OBD DTCs

As previously described, once a fault is detected, a 5-digit DTC is stored. This is a

standardized code which provides information about the type o f system or fault, which conforms

to the following format: 9



### • 

### Position 1: Device Code: B=Body; C=Chassis; P=Powertr ain; U=Network or data link

• 

### Position 2: Type: 0 = generic (legislated and common am ong all vehicle manufacturers);

1 = manufacturer specific

• 

### Position 3: Specific vehicle system:

— 1, 2 = Fuel and Air Metering

— 3 = Ignition System or Misfire

— 4 = Auxiliary Emission Controls

— 5 = Vehicle Speed Control and Idle Control System

— 6 = Computer Output Circuit

— 7, 8 = Transmission

• 

### Positions 4 and 5: These last two digits indicate which c omponent or system has a fault

As an example, P0455 is a powertrain (P) generic (0) code w hich involves an auxiliary

emission control system or component (4), and the last two digits indicate this is an “Evaporative

Emission Control System Leak Detected (gross leak)” 10 

### (this code is typical for a missing, faulty

9 SAE International, J1979 Surface Vehicle Standard, Iss ued 1991-12, Revised 2004-04, page 33.

10 Society of Automotive Engineers. (1999, March). On-Board D iagnostics for Light and Medium Duty Vehicles

Standards Manual, pg. 123.

### 2-4

or incorrectly installed gas cap, among other things). Af termarket scan tools and I/M analyzers

can access and download all generic powertrain (P0) codes, and other codes (such as

manufacturer-specific P1 codes) may be accessible by som e scanners and systems, including

specialized and manufacturer-specific diagnostic equipmen t.

Logic for setting a code varies depending on what system or component is being

monitored. Some codes are immediately set and the MIL is commanded “on” after only one

occurrence of a fault. However, PCM algorithms may re quire repeat failures on two successive

trips before the code is set and the MIL is commanded on. For these algorithms, if a fault is

identified on the first of two tests, a “pending” DTC is stored. If the fault is again detected on a

subsequent trip (generally the next consecutive trip), then the “pending” DTC becomes a

“confirmed” DTC, and the MIL is commanded on. On the oth er hand, if a fault is not identified

on the next trip, the “pending” DTC is erased (except for fuel and misfire monitoring codes,

which aren’t immediately deleted). Since “pending” DTCs indicate that there may be a problem

but this is not yet confirmed, the MIL is not commanded o n for a “pending” DTC. The MIL is

only commanded on for a confirmed DTC, whether it be a si ngle trip DTC or a two-trip DTC.

Once a confirmed DTC is stored, a snapshot of engine oper ating conditions at the time the code

was set is stored in the PCM’s memory. This snapshot of conditions is called freeze frame data

and offers clues that can help a repair technician identi fy and effectively repair the failure.

As previously described, the PCM can be “reset” (codes, fr eeze frame data and MIL

command “on” cleared) by disconnecting the vehicle’s batt ery or by using the reset feature of a

scan tool. This also resets all monitors to “not ready” . However, the PCM will also

automatically erase codes and freeze frame data and turn the MIL off if the fault which triggered

the DTC is not encountered during three consecutive tests 11 

### (again, excluding fuel and misfire

monitors, which are tested in a different manner whose description is beyond the scope of this

general description).

As a side note, a flashing MIL (as opposed to constant MI L illumination) indicates the

fault which has been detected poses an immediate threa t to the catalytic converter. 12 

### However,

an immediate threat to the catalytic converter isn’t always represented by a flashing MIL.

2.4 Evaporative Emissions Control System Overview

The focus of this report is on OBD monitoring of the eva porative emissions control

system. The general purpose of the evaporative emission s control system is to prevent release of

11 Birnbaum, R, & Truglia, J (2000). Getting to Know OBDII . asttraining.com, ISBN 0-9706711-0-5, pg, 26.

12 Birnbaum, R, & Truglia, J (2000). Getting to Know OBDII . asttraining.com, ISBN 0-9706711-0-5, pg, 24.

### 2-5

fuel vapor (raw hydrocarbons) into the atmosphere during vehi cle operation, hot soaks and

diurnal soaks. This is accomplished by a system design w hich reduces permeation and vapor

leaks from various materials and connections. Most of t he vapor is routed to a carbon canister

where it is stored and then released into the engine t o be burned at certain times during operation

of the engine.

Two overall types of evaporative system OBD monitoring e xist, non-enhanced and

enhanced systems. In general, non-enhanced systems only m onitor canister purge flow, while

enhanced systems monitor both purge flow and test for leaks in the vapor recovery system. 13



### Consequently, enhanced systems require leak detection senso rs and valves which aren’t required

in non-enhanced systems. In general, hardware for evapo rative emissions control systems may

include vapor transport lines, control solenoids and valve s, pumps, pressure sensors, and the

evaporative carbon canister.

2.5 Recent Evaporative Emissions Real World Test Pr ograms

The Coordinating Research Council (CRC) Real World Group has been conducting

permeation evaporative emissions testing in the E-77 and E -77-2 programs. 14 

### The permeation

test procedure was refined in the pilot E-77 program before using it in the larger E-77-2 program.

Most of the vehicles were specifically recruited as ag ing-enhanced evaporative emission

vehicles, model years 1996-2000. Three pre-enhanced evaporative em ission vehicles and one

newer near-zero emissions vehicle which met California PZEV evaporative requirements were

also tested. The focus was on non-ethanol fuel with bo th 7 and 9 RVP. The program also

evaluated 24-hour diurnals at the traditional temperature ra nge of 65-105 ° F and a higher

temperature diurnal of 85-120 ° F. A subset of the vehicles was tested for 72-hour diurnals . A leak

was implanted in the gas cap of one of the aging enhance d vehicles, and the series of tests were

run both before and after implanting the leak. The size of the leak was the minimum size

necessary for detection by OBD, 0.020” effective diameter as previously described, (although

federal OBD monitoring requirements specify detection of a 0.040” leak, most manufacturers

certify to California’s 0.020” in order to avoid the 49-state certification issue). The E-77 study

demonstrated that hydrocarbon emissions can be up to sever al orders of magnitude larger with an

13 Birnbaum, R, & Truglia, J (2000). Getting to Know OBDII . asttraining.com, ISBN 0-9706711-0-5, pg, 44.

14 CRC E-77 reports: Haskew, H; Liberty, T (2008) “Vehicle Eva porative Emission Mechanisms: A Pilot Study,

CRC Project E-77”, Haskew, H; Liberty, T (2010) “Enhanced Ev aporative Emission Vehicles (CRC E-77-2)”,

Haskew, H; Liberty, T (2010) “Evaporative Emissions from In-Use Vehicles: Test Fleet Expansion (CRC E-77-

2b)”, Haskew, H; Liberty, T (2010) “Study to Determine Eva porative Emission Breakdown, Including Permeation

Effects and Diurnal Emissions Using E20 Fuels on Aging Enhanced Evaporative Emissions Certified Vehicles, CRC

E-77-2c”

### 2-6

implanted leak. This established the need to define the ra te of occurrence of “leakers” in the fleet

in order to determine the overall impact on the inventory

.

During additional laboratory testing in the E-77-2 and E-77-2c programs, similarly-sized

leaks were implanted not only in the gas cap, but in other common locations identified during a

special study conducted in 2008 by CDPHE at the Lipan I/M sta tion (described later in this

section). The results indicated evaporative emission s leak rates are dependent on location of the

leak, in particular for vehicles not equipped with On-Board Refueling Vapor Recovery (ORVR).

Regardless of ORVR, higher leak rates were measured for leaks implanted at the top of the fuel

tank and at the inlet connection to evaporative control canister as compared to the gas cap.

The E-77 testing programs confirmed that both liquid and vapor leaks can be a significant

part of any hydrocarbon inventory. The missing piece of inf ormation is the prevalence of these

leaks in the fleet. A comprehensive program for quantifyi ng these vehicles in the existing fleet

has not been attempted since the American Petroleum In stitute’s “Raw Fuel Leak Survey in I/M

Lanes” study in 1998 15 

### or the California Bureau of Automotive Repair’s “Evaporat ive Emissions

Impact of Smog Check” study in 2000. 16 

### The current fleet consists of aging enhanced

evaporative emissions vehicles which were not part of or were quite new in these earlier studies.

During the summer of 2008, CDPHE provided access to the Lipan I/M station as well as

staff and remote sensing equipment for a study to determine the prevalence of vehicles with

evaporative leaks in the fleet. Certain model year 1981 a nd newer vehicles were selected (as

described in Reference 1) and offered participation in evapor ative emissions testing, which

consisted of a 15-minute hot-soak test in a portable SHED (P SHED), a visual, olfactory, and

electronic HC detector examination of vehicle fuel meteri ng and evaporative emissions control

system components. Measurements for a comparison of PS HED results with laboratory SHED

were also made on selected participating vehicles.

During the following summer of 2009, CDPHE and the Regional A ir Quality Council

(RAQC) performed a follow-on study with EPA reverting to an advisory role. This study was

performed at the Ken Caryl I/M station in Denver and was developed based on the Lipan

experience. Vehicles were selected (as described in Ref erence 2) and offered participation in

intensive evaporative emissions testing, which consisted o f the PSHED hot-soak test, visual,

olfactory, and electronic HC detector examination of the vehicle.

15 McClement, D. (1998) “Raw Fuel Leak Survey in I/M Lanes ,”

16 Amlin, D.; Carlisle, R.; Kishan, S.; Klausmeier, R. F.; Haskew, H. (2000) “Evaporative Emissions Impact of

Smog Check,”

### 2-7

Further work was continued in the summer of 2010 by the CDPHE and the RAQC in a

repair effectiveness study in which vehicles were brought t o and tested at CDPHE’s Aurora and

West Tech laboratories. In these efforts, SHED tes ts were performed followed by extensive

diagnostics and repairs. Repeat SHED tests were then performed on vehicles which had received

repairs.

Results from these studies suggest vapor leaks can have an impact on the inventory.

Traditional evaporative emissions testing, as well as the recent E-77 testing, have shown a range

of evaporative emissions from test vehicles, particular ly with aging vehicles. The higher

emissions levels (but lower than the “gross liquid leake rs”) have been associated with slow

growing vapor leaks which occur as the evaporative emissions control systems age. Vehicles

with current (Tier 2 and Enhanced) evaporative emissions c ontrol technology are now starting to

age, and information on the prevalence of these higher em issions vehicles in the fleet is still

being collected.

### 3-1



## 3.0 Analysis

This analysis involves the comparison of information on OBD evaporative system DTCs

with SHED results for the same vehicles. It is not i ntended to find prevalence rates with OBD

evaporative codes. The dataset was drawn from three set s of data: the participants in the High

Evaporative Emission studies from 1) the summer of 2008 at the Lipan I/M testing station in

Denver, Colorado, 2) the summer of 2009 at the Ken Caryl I/ M testing station in Denver,

Colorado, and 3) the summer and fall of 2010 at the CDPHE A urora and West Tech laboratories

in Denver, Colorado. Each of these three datasets include vehicles that were tested for

evaporative emissions using a PSHED for 15 minutes (at the Aurora station the vehicles were

tested using an LSHED for 1 hour, but only the first 15 mi nutes of continuous measurement were

used in this analysis to compare with the PSHEDs).

The I/M dataset included 1996 and newer vehicles. Records for v ehicles whose I/M

inspections were aborted or incomplete due to OBD communic ation problems were removed

from the dataset. The excluded vehicles are described in more detail in Sections 3.1 (Data

Preparation) and 3.2 (Data Analysis Results). Each vehic le’s SHED results were then matched

with the OBD test that was performed immediately befor e the SHED test.

In the case of the Lipan and Ken Caryl high evaporative field studies, the vehicles

received an OBD test as part of their regular I/M insp ection prior to solicitation for participation

in the study. Therefore, the OBD test usually happened several hours or even a day before the

SHED test occurred. Therefore, because the vehicle wa s solicited during the I/M inspection

(immediately before or just after the I/M test was performed, before the motorist left the facility)

and was then retained by the staff performing the high eva porative emissions study, it was still in

the same repair state for both the SHED test and the O BD test.

In the case of the summer 2010 high evaporative emissions study performed at CDPHE’s

West Tech and Aurora laboratories, vehicles were solicited by letter and then brought to the

vehicle test station by the owner. The vehicle was kept for several days by the CDPHE staff and

SHED tested several times, before and after repair. E ach time a SHED test was performed, a

series of six IM240 tests were performed just prior to th e SHED test in order to condition the

vehicle for the SHED testing. The last IM240 with OBD t est that was performed of the six prior

to the SHED test was used to match with the SHED testi ng for this analysis. Only the before

repair test for each of the vehicles in this dataset wa s used for each vehicle to limit the analysis to

“as received” condition.

### 3-2

The specific number of OBD/SHED data pairs available is described for each of the three

datasets below. The overall results for the three da tasets combined are described in the Data

Analysis Results section after that.

3.1 Data Preparation

Twenty-four PSHED tests were conducted on 24 vehicles during the Lipan High

Evaporative Emissions Field Study conducted in the summer of 2008. ERG successfully

matched 17 of these 24 PSHED results with each vehicle’s I/ M OBD results (the I/M test was

either aborted or did not contain OBD data for the other 7 tests - OBD is advisory only in the

Colorado I/M program, meaning no pass or fail is assigned based on OBDII results). Similarly,

89 PSHED tests were conducted on 89 vehicles during the Ken Caryl High Evaporative

Emissions Field Study, and ERG successfully matched 76 of th ese 89 records with

corresponding OBD results (as before, the I/M test was either aborted or did not contain OBD

data for the other 13 tests).

Eighty-seven PSHED/SHED tests were conducted on 68 vehic les during the Denver 2010

study (some of the 68 vehicles in the Denver 2010 study received two tests, a “before repair” and

an “after repair” test). ERG was able to successful ly match all 87 of the Denver 2010 study

PSHED/SHED results with valid OBD results. Table 3-1 pro vides a summary of the final

datasets used in this analysis. As shown in this table, in total, ERG successfully matched results

from 180 PHED/SHED tests with OBD data. Results for co mparison of OBD evaporative codes

with PSHED/SHED results are provided in the following se ction.

Table 3

- 1

. Summary of Matched SHED and I/M Records used in Analysis

Study Total # of

Vehicles Total # of

PSHED/SHED

Tests “Dropped” P S HED /SHED

Tests (those with no

corresponding OBD record) Remaining PSHED/ SHED

Tests matched with OBD

records

Lipan 24 24 7 17

Ken Caryl 89 89 13 76

Denver 2010 68 87 0 87

Total 181 200 20 180



### 3.2 Data Analysis Results

As shown in the last column of Table 3-1, when the part icipant vehicle tests from each of

the three studies were combined, there were a total of 180 P SHED/SHED tests with valid OBD

matches (for the remainder of this report, both PSHED an d SHED results will be generically

referred to as “SHED” results for clarity). However, some of these SHED tests were performed

### 3-3

after the vehicle was repaired. These after-repair SHE D results have been removed from the

analysis. Also, some of the SHED and OBD test pairs had an evaporative OBD monitor status of

“Not Ready” at the time of the OBD test, so these te st pairs have also been removed from this

analysis. Table 3-2 summarizes the remaining vehicle SHE D and OBD pairs after application of

each of these filters.

In this analysis, only test results with “confirmed” eva porative-related DTCs (DTCs in

the range P0440 to P0469 with a MIL command status of “on”) we re considered. No “Pending”

evaporative DTCs (DTCs in the range P0440 to P0469 but which we re “pending” as described in

Section 2.3, OBD DTCs) were identified in the data used fo r this analysis.

Table 3

- 2

. Pair Counts for MY96 Lipan, Ken Caryl, and Denver H igh Evap Study

Participants Combined

SHED/OBD Test Pairs

Total matched SHED/OBD test pairs 180

Before r epair SHED/OBD test pairs 157

Before repair t est p airs with evaporative system monitor status of “Ready” 149

Before repair test pairs with evaporative monitor status o f “Ready” and

with no confirmed DTCs 145

Before repair test pairs with evaporative monitor status o f “Ready” and

with confirmed DTCs and MIL commanded “on” 4



### 3.3 Comparison of SHED Values to Presence of OBD Ev aporative System DTCs

To compare the OBD and SHED results for each matched pai r of records, each SHED

result was defined as either high or low using two SHED cu t point values; either 0.3 grams of

total HC emissions per 15 minutes (0.3 g/Qhr), or 1 gram of tota l HC emissions per 15 minutes

(1 g/Qhr). Separate analyses were performed by defining “hi gh” SHED test results above each

of these cut points or below each of these cut points. The SHED cut point of 1 g/Qhr was used

because it was found to be the approximate average emissi on level for the first fifteen minutes of

a laboratory Hot Soak of implanted leaks with 0.02” diam eter (the minimum detectable diameter

of the evaporative OBD systems) in the Coordinating Res earch Council (CRC) E-77 test

programs. 17 

### The 0.3 g/Qhr cut point is an estimate of a 15-minute h ot-soak portion of the 2 g/hr

Diurnal + Hot Soak enhanced evaporative emission standar d. This value was derived from the 2

g/hr Diurnal + Hot Soak enhanced evaporative emission sta ndard by assuming 20% of the 2 g/hr

emissions are due to Hot Soak, and then assuming 75% of th at would be in the first 15 minutes.

17 It was found that when leaks were implanted at the gas c ap on an ORVR equipped vehicle the emission levels

were contained. This effect will be system dependent, and it is therefore likely that some designs of ORVR vehic les

would show uncontrolled levels of emissions for a leak. T he average discussed here is approximate for the

implanted leak locations at the canister connection and at the top of the tank.

### 3-4

The SHED values were compared for pairs with and without confirmed evaporative

system DTCs. It can be seen from Table 3-2 that only 4 o f the 145 records had confirmed

evaporative DTCs stored. Tables Table 3-3 and Table 3-4 co mpare the number of paired

records with confirmed evaporative DTCs and high/low SHED classification for 1 g/Qhr and 0.3

g/Qhr, respectively. As stated earlier, these tables a re provide a comparison of OBD-equipped

vehicles that were measured with a SHED test, but due to the recruitment methods (see

references (1) and (2)), the percentages in these tables are not intended to be representative of the

fleet. The tables also list the percentages of pairs w ithin the four quadrants for each row and

column. All 4 paired records with confirmed evaporative DTCs had high corresponding SHED

values (when defining “high” as 0.3 g/Qhr) and 75% had confirmed evaporative DTCs when

defining “high” as 1.0 g/Qhr. In contrast, 12% of the 145 pairs with no confirmed evaporative

DTCs had high SHED values (with a 1.0 g/Qhr cut point) an d 16% were “high” at the 0.3 g/Qhr

cut point. In both Table 3-3 and Table 3-4, 85% of the vehicl es with high SHED values did not

have a confirmed evaporative DTC. This could be due to a num ber of reasons, such as the fact

that not all high evaporative emissions are due to vapor l eaks which the OBD system is designed

to identify, but the high percentages does indicate additio nal investigation is warranted.

Table 3

- 3

. Number of Pairs with Evap DTCs Set Versus High and

Low SHEDs (1.0 g/Qhr cutpoint)

OBD Evap DTCs not set OBD Evap DTCs set Total

HIGH SHED

(> 1.0 g/15 minutes) 17 Vehicles

(85% of 20)

(12% of 145) 3 Vehicles

(15% of 20)

(75% of 4) 20 Vehicles

LOW SHED (<=

1.0 g/15minutes) 128 Vehicles

(99% of 129)

( 88% of 145) 1 Vehicles

(1% of 129)

(25% of 4) 129 Vehicles

Total 145 Vehicles 4 Vehicles 149 Vehicles



### Table 3

- 4

. Number of Pairs with Evap DTCs Set Versus High and

Low SHEDs (0.3 g/Qhr cutpoint)

OBD Evap DTCs

not set OBD Evap DTCs

set Total

HIGH SHED

(> 0.3 g/15/minutes) 23 Vehicles

(85% of 27)

(16% of 145) 4 Vehicles

(15% of 27)

(100% of 4) 27 Vehicles

LOW SHED

(<= 0.3 g/15 minutes) 122 Vehicles

(100% of 122)

( 84% of 145) 0 Vehicles

(0% of 122)

(0% of 4) 122 Vehicles

Total 145 Vehicles 4 Vehicles 149 Vehicles

### 3-5

Table 3-5 provides additional vehicle and test information fo r vehicles with SHED results

above the 1 g/Qhr designated threshold, including the packet ID, vehicle make, model year,

model and the evaporative certification family for the vehicle. The “evap_mon_ready” column

describes the readiness status of the vehicle’s evapora tive system monitor. Table 3-5 also lists

DTCs that were downloaded at the time of the OBD test and indicates whether or not the DTCs

were categorized as evaporative DTCs (confirmed DTCs in the range of P0440 to P0469). A

footnote in the table provides definitions of the evaporat ive DTCs. Additional information on

these vehicles and all vehicles with PSHEDs > .3 g/Qhr , including non-ready OBD evaporative

monitor vehicles, is provided in the appendix of this report.

Table 3-5 also lists comments provided by the vehicle inspecto rs as they tried to identify

the source of the vapor leaks using a hand held HC vapor dete ctor. In many instances, the

vehicle vapor lines were inaccessible. Some were behind sheet metal shrouds and no intrusive

process was undertaken to get behind these coverings. Based o n the inspector comments, the

make and model year of the vehicle, and any other visual e vidence, ERG and OTAQ made a

determination regarding whether or not a malfunction shoul d be detectable by the vehicle’s OBD

system. This determination is listed in the column lab eled “Should Problem be Detectable by

OBD?” If the vehicle inspector was not able to identify the source of the leak, then a

determination was not made regarding whether or not the OBD system should have been able to

detect the malfunction, and a “?” is listed in the tab le. The areas of the fuel system inaccessible

to the HC detector, as mentioned above, were behind shro uds, above the fuel tank, or within

bundles of hoses packed too tightly to be reached by the HC detector probe. Due to their

locations and lack of evidence of a liquid leak, leaks loca ted in these inaccessible areas were

likely to be a vapor leaks, rather than liquid leaks. L iquid leaks would likely occur at connection

points in the fuel line or the fuel rail and would likely be detectable by the handheld detector. It

is unlikely these liquid leaks would be detectable by the OBD systems for most vehicles, since

OBD systems are not designed to detect liquid leaks.3-6Table3-5.Details for Vehicles with SHED Results > 1 g/Qhr (excluding liquid and unmonitored vapor leaks)Table 3-5APacketID Evap Family DatasetModelYear Make ModelSHED_g/15min PSHED_over_1g HC evap_DTCLIP-222FJXR01251BBLIPAN2002SUBARUIMPREZA1.30YesNoCRL-540.CARYL1998HONDAACCORD2.10YesNoLIP-256XGMXR0124912LIPAN1999OLDSALERO2.18YesNoCRL-475YGMXE0111911CARYL2000CHEVASTRO VAN2.45YesNoHE-6725WTYXE0095AE1DENVER1998TOYOTACAMRY6.30YesNoLIP-193WFMXE0045AAALIPAN1998FORDMUSTANG11.22YesNoHE-6763VFM1057BYMADENVER1997MERCURYVILLAGER20.81YesNoHE-60112FJXR01251CCDENVER2002SUBALEGACY5.21YesYesHE-6799TFM2045AYPBADENVER1996FORDRANGER12.21YesYesHE-6018WFMXE0115BAEDENVER1998FORDTAURUS19.93YesYesTable 3-5BPacketIDEvap Family Dataset evap_mon_readyDTC codesShouldMalfunctionbeDetectable by OBD?Vapor/ Liquid/ No LeakIdentifiedLIP-222FJXR01251BBLIPANYes-Not ascertainable*,**No LeakIdentifiedCRL-540.CARYLYes-Not ascertainable*, **VaporLIP-256XGMXR0124912LIPANNo-Not ascertainable*, **No LeakIdentifiedCRL-475YGMXE0111911CARYLNo-Yes**VaporHE-6725WTYXE0095AE1DENVERYes-Yes***VaporLIP-193WFMXE0045AAALIPANYes-Not ascertainable*, ***No LeakIdentifiedHE-6763VFM1057BYMADENVERYes-yes-purge solenoidVaporHE-60112FJXR01251CCDENVERYes451|457Yes***VaporHE-6799TFM2045AYPBADENVERYes443Yes-purge solenoidVaporHE-6018WFMXE0115BAEDENVERYes443Yes-purge solenoidVapor*The source of the high SHED emissions could not be determined from the technician comments in the field studies.**Manufacturer and EPA certification representatives have stated that these manufacturers are certified to California enhanced OBD requirement of a 0.020”diameter orifice detection capability.***The magnitude of the emissions indicates that this would have been equivalent to at least a 0.040” diameter orificeand therefore should have been detectedby Federal OBD.3-7Table 3-5CPacketIDEvap FamilyDatasetInspectorCommentsLIP-222FJXR01251BBLIPANNothing FoundCRL-540 . CARYLSniffer leak detected at vapor canister. No non-OEM installations. Did not find fuel filter.Canister leak = vapor not liquid.LIP-256XGMXR0124912LIPANNothing FoundCRL-475 YGMXE0111911 CARYLSuspect that fuel pump replacement damaged gasket. Areas ontop of tank and near tank to fillpipe connect set sniffer off. Also evap canister set sniffer off. No access to engine and that partof fuel system.HE-6725WTYXE0095AE1DENVERGas cap was causeof leak.LIP-193WFMXE0045AAALIPANNothing FoundHE-6763VFM1057BYMADENVERVapor/purge hose cracked.HE-60112FJXR01251CCDENVERVapor lines at the top of filler neck not connected.HE-6799 TFM2045AYPBA DENVERFound wires corroded/broken thatactivated the purge valve. Supplying power and groundshowed the purge valve did not operate. Removed canister and evacuated over night.HE-6018WFMXE0115BAEDENVERExtreme HC odor at right rear. Exhaust collector is right behind this area.Table 3-5 Legend• P0440 Evaporative Emission Control System Malfunction• P0441 Evaporative Emission Control System Incorrect Purge Flow• P0442 Evaporative Emission Control System Leak Detected (small leak)• P0443 Evaporative Emission Control System Purge ControlValve Circuit• P0444 Evaporative Emission Control System Purge ControlValve CircuitOpen• P0445 Evaporative Emission Control System Purge ControlValve CircuitShorted• P0446 Evaporative Emission Control System Vent Control CircuitMalfunction• P0447 Evaporative Emission Control System Vent Control Circuit Open• P0448 Evaporative Emission Control System Vent Control Circuit Shorted• P0449 Evaporative Emission Control System Vent Valve/Solenoid CircuitMalfunction• P0451 Evaporative Emission Control System Pressure SensorRange/Performance• P0452 Evaporative Emission Control System Pressure Sensor Low Input• P0453 Evaporative Emission Control System Pressure Sensor High Input• P0454 Evaporative Emission Control System Pressure Sensor Intermittent• P0455 Evaporative Emission Control System Leak Detected (gross leak)• P0456 Evaporative Emissions System Small Leak Detected• P0457 Evaporative Emission Control System Leak Detected• P0458 Evaporative Emission System Purge Control Valve Circuit Low• P0459 Evaporative Emission System Purge Control Valve Circuit High• P0465 Purge Flow Sensor Circuit Malfunction• P0466 Purge Flow Sensor Circuit Range/Performance• P0467 Purge Flow Sensor Circuit Low Input• P0468 Purge Flow Sensor Circuit High Input• P0469 Purge Flow Sensor Circuit Intermittent• P0450 Evaporative Emission Control System Pressure Sensor Malfunction

### 3-8

As shown in Table 3-3, twenty vehicles with an evaporativ e system monitor status of

“ready” had SHED measurements greater than 1 g/Qhr. Det ails of these 20 vehicles are listed in

Appendix A. However, it can be seen that only 10 vehicle s with SHED measurements greater

than 1 g/Qhr are listed in Table 3-5, and of these only 8 hav e evaporative monitors with a

“ready” status (as opposed to all 20 vehicles in Table 3-3). The following reasons explain

differences between the “ready” vehicles emitting grea ter than 1 g/Qhr in Table 3-5 and the

vehicles listed in Table 3-3:

• 

### Table 3-5 includes two vehicles (vehicles associated with pac ket IDs LIP-256 and

CRL-475) whose evaporative system monitor status was “not ready” (these are

not included in the counts provided in Table 3-3). Appendix A pr ovides details of

vehicles with both “ready” and “not ready” evaporative system monitors.

• 

### OBD evaporative system monitoring is not designed to identif y liquid leaks;

since Table 3-5 was developed to assess OBD’s ability to iden tify monitored

vapor leaks, these vehicles with (unmonitored) liquid leaks which are included in

Table 3-3 are not listed in Table 3-5.

• 

### Since many 1996 and 1997 vehicles which conform to Federal (non-C alifornia)

standards were only designed to monitor purge solenoid check s but not vapor

leaks 18 

### , those model year 1996 and 1997 vehicles included in Table 3-3 for which

the inspection indicated the malfunction was anything other than a purge solenoid

were excluded from Table 3-5, as these would be malfunctio ns not monitored by

OBD. Again, details on each of these vehicles are provi ded in Appendix A.

• 

### As OBD requirements developed and phased in, it became com mon practice for

auto companies, such as those listed in Table 3-5, to certif y to the California OBD

leak detection standard of 0.020” all of their vehicles sold f ederally. Laboratory

data has shown a 0.020” diameter orifice to be roughly equi valent to an emission

rate of 1 g/Qhr. Using the formula for the area of a circle ( π r 2 

### ), it can be seen that

the magnitude of emissions quadruples with the doubling of the d iameter size to

0.040”, and this has been found to be the case with laborato ry testing comparing

0.020” and 0.040” leaks. Consequently, based on the magnitude of emissions, for

the vehicles in Table 3-5 with SHED emissions of 6.30 g/Qhr and greater, it is

reasonable to assume that they have leaks of diameter 0.040”.

Based on these two datasets, this preliminary analysis sugge sts that OBD systems did not

identify 50-70% of the potential high evaporative emitters i n these studies. The lower range,

50% (3 out of 6), is based on the occurrences of when th e OBD system should probably have

detected the leak from a known source based on the technic ian comments, disregarding the “?”

vehicles in the “Should Malfunction be Detectable by OB D?” column. The higher range, 70% (7

18 40 CFR 86.094-17

### 3-9

out of 10), includes the unknown leak sources (“?”) for whi ch no leak was identified or the vapor

leak was likely located in the area of the evaporative control system inaccessible to the HC

detector. Liquid leaks (which would generally not be monito red by OBD) were not included in

this estimate.

It should be noted that this preliminary analysis was bas ed on a qualitative review of the

technician comments, rather than a quantitative assess ment of OBD monitoring criteria (such as

a pressure drop associated with a 0.020” or 0.040” diameter orif ice leak). In addition, since 2 of

these 10 vehicles had a “not ready” evaporative system monit or, it is possible that the vehicle’s

OBD system would have detected the leak and stored a DTC o nce the evaporative system

monitor achieved readiness. However, as most I/M progra ms in the United States typically allow

1 to 2 “not ready” monitors, these vehicles could potential ly pass an I/M OBD inspection with

these types of evaporative system failures before the m onitor achieved readiness.

Some of the vehicles in these studies were model year 1996 through 1998 vehicles and

therefore may not have been equipped with OBD enhanced ev aporative system monitoring. For

these older vehicles, some of the evaporative system fa ilures could be undetectable by the OBD

systems installed on those vehicles. ERG compared the m odel year distributions with high/low

SHED categories to determine if a correlation existed b etween SHED values and vehicle model

year. The high SHED pairs included vehicles with model years from 1996-2003, and the low

SHED pairs included vehicles with model years from 1996-2010. This suggests that high SHED

results tended to be associated with older model year vehi cles. Table 3-6 lists model year counts

for high and low SHED pairs vehicles of model year 1996-2010 in the dataset.

Table 3

- 6

. Model year Counts for High and Low SHED Pairs in th e Data

Model

Year SHED Cut P oint of 1.0 g/Qhr SHED Cut P oint of 0.3 g/Qhr

# of Pairs with

SHED Value High # of Pairs with

SHED Value Low # of Pairs with

SHED Value High # of Pairs with

SHED Value Low

1996 5 9 7 7

1997 7 1 3 9 11

1998 4 1 0 4 10

1999

- 1 0 1 9

2000 2 1 2 2 12

2001

- 15 1 14

2002 2 1 7 2 1 7

2003

- 12 1 11

2004

- 9

- 9

2005

- 13

- 13

2006

- - - -

2007

- 1

- 1

### 3-10

Table 3

- 6

. Model year Counts for High and Low SHED Pairs in th e Data

Model

Year SHED Cut P oint of 1.0 g/Qhr SHED Cut P oint of 0.3 g/Qhr

# of Pairs with

SHED Value High # of Pairs with

SHED Value Low # of Pairs with

SHED Value High # of Pairs with

SHED Value Low

2008

- 2

- 2

2009

- 4

- 4

2010

- 2

- 2

Total

Vehicles 2 0 129 27 122

### 4-1



## 4.0 Conclusions

Three different datasets were used in this study to determ ine if high evaporative emitters,

as defined by LSHED or PSHED tests, were appropriately identi fied by each vehicle’s OBD

system. Although the total number of observations was l imited, this analysis indicates that many

vehicles with high SHED values (hot-soak emissions equal to or greater than 1 g/Qhr as

measured by a SHED test) do not have stored evaporative DTCs or MILs. For vehicles with

high SHED HC measurement results, an attempt was made t o determine the source of the vapor

leak. Results are shown in Table 4-1, which summarizes pertinent information for all vehicles

listed in Table 3-5. Due to the configuration of the vehic le chassis the source or sources of each

leak could not always be isolated. Table 4-1 shows that O BD systems did not identify 50-70% of

the high evaporative emitters in these studies (for va rious reasons including “not ready”

evaporative system monitors). The lower range, 50% (3 out of 6), is based on evaporative

system failures that should probably have been detected by the OBD system. The higher range,

70% (7 out of 10), includes vehicles for which no leak source was identified or the vapor leak

was likely located in an area of the evaporative contr ol system inaccessible to the HC detector

(“Not ascertained” in Table 4-1). Liquid leaks (which gene rally are not monitored by OBD)

were not included in this estimate.

From an overall perspective, this study identified 29 vehicle s (27 listed in Table 3-4 plus

2 with “not ready” evaporative monitors) with PSHED valu es greater than 0.3 g/Qhr (roughly

equivalent to the hot-soak component of the 2 g/hr Diurna l + Hot Soak standard), and only 4 of

those 29 vehicles had stored evaporative DTCs. Two vehicle s had “not ready” evaporative

monitors. The source of elevated evaporative emissions from the remaining 23 “ready” vehicles

which had no evaporative DTCs was either undetectable by c urrent OBD design (for example, a

hidden liquid leak not observed by field technicians), was from a part of the system not

monitored by OBD, or was a vapor leak which should have bee n identified but was not (i.e., the

evaporative emissions monitoring system was malfunctioning in some way).

No “OBD false positive” vehicles were identified in thi s study (those with stored

evaporative system DTCs with SHED emissions under 0.3 g/Qh r). The preferential recruiting of

vehicles with high evaporative emissions would tend to reduc e the likelihood of this category of

vehicles from participation in these studies, so no conc lusions can be drawn from the lack of

these vehicles in these results. However, the key fi nding of this report is the high number of

vehicles with high evaporative emissions which were not i dentified by the OBD evaporative

system.

### 4-2

Since the sample size used for this analysis was limit ed to ten vehicles which were

expected to set DTCs, EPA sought to enhance our understanding w ith larger OBD datasets.

Analysis was performed using inspection and maintenance data from Texas and California.

Preliminary conclusions from detailed analysis of data fr om these states complement the

conclusions of this report and can be found in Appendix B.

Table 4-1. Comparison of SHED and OBD Results for Vehicles with SHED

Emissions > 1 g/Qhr (Summary of Information for Veh icles Listed in Table 3-5)

Data Set Model

Year SHED

g/15

min Evap

DTC Evap

Monitor

Ready Evaporative

DTC code Should Malfunction

be detectable by

OBD?

Lipan 2002 1.30 No Yes - Not ascertainable*, **

Ken Caryl 1998 2.10 No Yes - Not ascertainable*, **

Lipan 1999 2.18 No No - Not ascertainable*, **

Ken Caryl 2000 2.45 No No - Yes**

Denver 1998 6.30 No Yes - Yes***

Lipan 1998 11.22 No Yes - Not ascertainable*, ***

Denver 1997 20.81 No Yes - Yes – purge solenoid

Denver 2002 5.21 Yes Yes 451/457 Yes***

Denver 1996 12.21 Yes Yes 443 Yes – purge solenoid

Denver 1998 19.93 Yes Yes 443 Yes – purge solenoid

*The source of the high SHED emissions could not be determ ined from the technician comments in the field studies.

**Manufacuter and EPA certification representatives have stated that these manufacturers certified to Californi a

enhanced OBD requirement of a 0.020” diameter orifice detect ion capability.

*** the magnitude of the emissions indicates that this would have been equivalent to at least a 0.040” diameter

orifice and therefore should have been detected by OBD on a federally certified vehicle

### Appendix AA-1Appendix A: Details for All Study Vehicles with SHED Results > 0.3 g/QhrPacketIDEvap FamilyDatasetModel YearMakeModelSHEDg/15minPSHED> 1PSHED> .3evapDTCevapmonitorreadyDTC codesLIP-254TCR1073AYPBPLIPAN1996JEEPCHEROKEE0.33NoYesNoY.|.|.|.|.CRL-568VGM1035AYPAACARYL1997STRNSL0.39NoYesNoY733|734|.|.|.CRL-393.CARYL2001TOYOTASOLARA0.46NoYesNoY1135|1155|.|.|.CRL-546TNT1047DYMAOCARYL1996GEOPRIZM0.62NoYesNoY.|.|.|.|.HE-6454XFMXE0120BAEDENVER1999MERCURYMOUNTAINEER0.67NoYesNoY.|.|.|.|.CRL-395VGM1095AYMEACARYL1997CHEVS100.72NoYesNoY172|175|.|.|.CRL-271VGM1098AYMBACARYL1997GMCSIERRA1.28YesYesNoY.|.|.|.|.LIP-222FJXR01251BBLIPAN2002SUBAIMPREZA1.30YesYesNoY.|.|.|.|.HE-6418VFM1065BYMAADENVER1997FORDASPIRE1.47YesYesNoY.|.|.|.|.CRL-540.CARYL1998HONDACCORD2.10YesYesNoY.|.|.|.|.LIP-256XGMXR0124912LIPAN1999OLDSALERO2.18YesYesNoN.|.|.|.|.CRL-357VNS1110AYMEACARYL1997NISSPATHFINDER2.32YesYesNoY325|1447|.|.|.CRL-475YGMXE0111911CARYL2000CHEVASTRO VAN2.45YesYesNoN.|.|.|.|.HE-6331TFM1045AYPABDENVER1996FORDCONTOUR2.79YesYesNoY133|304|.|.|.HE-6609YGMXE0095905DENVER2000OLDSBRAVADA5.77YesYesNoY.|.|.|.|.CRL-85TCR1073AYPOBCARYL1996DODGRAM 15006.08YesYesNoY.|.|.|.|.HE-6725WTYXE0095AE1DENVER1998TOYOTACAMRY6.30YesYesNoY420|.|.|.|.HE-6647YSZXT0095ME0DENVER2000ISUZURODEO8.65YesYesNoY401|463|171|172|174HE-6759VGM1070AYMAADENVER1997OLDSDELTA 889.10YesYesNoY.|.|.|.|.LIP-193WFMXE0045AAALIPAN1998FORDMUSTANG11.22YesYesNoY.|.|.|.|.CRL-321VGM1095AYMEACARYL1997CHEVS1012.33YesYesNoY.|.|.|.|.HE-6620TNS1057BYMBBDENVER1996NISSQUEST12.79YesYesNoY400|325|.|.|.HE-6519YTY1047DYMA0DENVER1997TOYTCOROLLA16.41YesYesNoY.|.|.|.|.HE-6702TGM1089AYMEADENVER1996CHEVCAVALIER19.53YesYesNoY.|.|.|.|.HE-6763VFM1057BYMADENVER1997MERCURYVILLAGER20.81YesYesNoY325|300|.|.|.CRL-3163HYXR0105PEACARYL2003HYUNACCENT0.69NoYesYesY442|650|463|.|.HE-60112FJXR01251CCDENVER2002SUBALEGACY5.21YesYesYesY451|457|420|.|.HE-6799TFM2045AYPBADENVER1996FORDRANGER12.21YesYesYesY443|.|.|.|.HE-6018WFMXE0115BAEDENVER1998FORDTAURUS19.93YesYesYesY1518|443|.|.|.A-2Appendix A: Details for All Study Vehicles with SHED Results > 0.3 g/QhrPacketIDEvap FamilyDatasetModel YearMakeModelShouldMalfunctionbedetectableby OBD?Vapor/Liquid/NoLeakFoundCommentsLIP-254TCR1073AYPBPLIPAN1996JEEPCHEROKEEno evapcodes yet*VaporGas cap IM failure. MCM Comments:Nothing found.CRL-568 VGM1035AYPAA CARYL 1997 STRN SLno evapcodes yet* VaporGas cap IM failure. MCMComments:Sniffer goes off inconsistently in areaof fuel tank especially around top.Odor of gasoline under vehicle in fueltank area.CRL-393.CARYL2001TOYOTASOLARA?VaporUnderbody-fuel lines not visible butaccessible to sniffer. Fuel injectorspretty much hidden below intakemanifold.CRL-546 TNT1047DYMAO CARYL 1996GEOPRIZMno evapcodes yet* VaporWhile lying below fuel tank area Ithought I got a faint whiff of gasoline.Bruce said same as we were closingPSHED door.HE-6454XFMXE0120BAEDENVER1999MERCURYMOUNTAINEER?NoLeakFoundNo commentsCRL-395 VGM1095AYMEA CARYL 1997 CHEV S10no evapcodes yet* VaporTank is severely dented. Cannot seeliquid fuel but top of fuel tankactivates sniffer. Can hear fuel pumpwhining while driving.CRL-271VGM1098AYMBACARYL1997GMCSIERRAno evapcodes yet*VaporCannot see filler to tank connection.Fuel tank skid plate has some damage.Around top of tank on fill pipe side(right) the sniffer went off particularlynear the front of tank.LIP-22 2FJXR01251BB LIPAN 2002 SUBA IMPREZA ?NoLeakFound Nothing FoundA-3Appendix A: Details for All Study Vehicles with SHED Results > 0.3 g/QhrPacketIDEvap FamilyDatasetModel YearMakeModelShouldMalfunctionbedetectableby OBD?Vapor/Liquid/NoLeakFoundCommentsHE-6418VFM1065BYMAADENVER1997FORDASPIREno evapcodes yet*VaporNo visible liquid leaks, butoccasionalHC from gas analyzer. Filter mount isbroken. Fuel filter was replaced, andthe mount was repaired. Fuel spilleddown the driver's side strut mountduring replacement. This was pickedup during after repair 1 test.CRL-540 . CARYL 1998 HOND ACCORD ? VaporSniffer leak detected at vapor canister.No non-OEM installations. Did notfind fuel filter. Canister leak = vapornot liquid.LIP-256XGMXR0124912LIPAN1999OLDSALERO?NoLeakFoundNothing FoundCRL-357 VNS1110AYMEA CARYL 1997 NISS PATHFINDERno evapcodes yet* VaporThere is some sort of contraption thatsets sniffer off back between fuel tankand canister (see photo).CRL-475YGMXE0111911CARYL2000CHEVASTRO VANyesVaporSuspect that fuel pump replacementdamaged gasket. Areas on top of tankand near tank to fill pipe connect setsniffer off. Also evap canister setsniffer off. No access to engine andthat part of fuel system.HE-6331 TFM1045AYPAB DENVER 1996 FORD CONTOURno evapcodes yet* Vapor Significant HC from top of tank.HE-6609YGMXE0095905DENVER2000OLDSBRAVADAnoLiquidVisible fuel stainage bottom of tank.CRL-85 TCR1073AYPOB CARYL 1996 DODG RAM 1500no evapcodes yet* LiquidTank looks stained possiblyfromgasoline. I can smell gasoline whenlying under vehicle by filler neck.The vent line clamp is rusted andlooks like it has been wet but sniffer isinconsistent about sensing fumes inthat area.A-4Appendix A: Details for All Study Vehicles with SHED Results > 0.3 g/QhrPacketIDEvap FamilyDatasetModel YearMakeModelShouldMalfunctionbedetectableby OBD?Vapor/Liquid/NoLeakFoundCommentsHE-6725WTYXE0095AE1DENVER1998TOYOTACAMRYyesVaporGas cap was cause of leak.HE-6647 YSZXT0095ME0 DENVER 2000 ISUZU RODEO no VaporThere is a fuel odor under hood.Sniffer in V_engine valley underintake manifold sets it off.HE-6759VGM1070AYMAADENVER1997OLDSDELTA 88no evapcodes yet*NoLeakFoundNo commentsLIP-193 WFMXE0045AAA LIPAN 1998 FORD MUSTANG ?NoLeakFound Nothing FoundCRL-321VGM1095AYMEACARYL1997CHEVS10no evapcodes yet*LiquidMajor gasoline leak with gas puddlingon engine. Not sure where leak isexactly. Some part of supply orinjector to TBI system?HE-6620 TNS1057BYMBB DENVER 1996 NISS QUESTno evapcodes yet* VaporMajor HC at mid tank area, driver'sside.HE-6519YTY1047DYMA0DENVER1997TOYTCOROLLAno evapcodes yet*NoLeakFoundNo comments on MCMtest.Comment on repair note said that thetrouble code indicated P0401 EGRflow. Investigate to see why this wasnot in IM.HE-6702 TGM1089AYMEA DENVER 1996 CHEV CAVALIERno evapcodes yet* Liquid#3 fuel injector leaks, gas cap ismissing, #1 fuel injector startedleaking.HE-6763VFM1057BYMADENVER1997MERCURYVILLAGERyes-purgesolenoidVaporVapor/purge hose cracked.CRL-316 3HYXR0105PEA CARYL 2003 HYUN ACCENTsmall leak -.02", fuellevel sensor VaporSomething seems to be damaged orleaking at top of fuel tank. Snifferactive many places around top pipe totank joint. Looks dry - tank appears tohave evaporated fluid of some kindbut that did not activate sniffer.A-5Appendix A: Details for All Study Vehicles with SHED Results > 0.3 g/QhrPacketIDEvap FamilyDatasetModel YearMakeModelShouldMalfunctionbedetectableby OBD?Vapor/Liquid/NoLeakFoundCommentsHE-60112FJXR01251CCDENVER2002SUBALEGACYVaporVapor lines at the top of filler neck notconnected.HE-6799 TFM2045AYPBA DENVER 1996 FORD RANGERpurgesolenoid VaporFound wires corroded/broken thatactivated the purge valve. Supplyingpower and ground showed the purgevalve did not operate. Removedcanister and evacuated over night.HE-6018WFMXE0115BAEDENVER1998FORDTAURUSpurgesolenoidVaporExtreme HC odor at right rear.Exhaust collector is right behind thisarea.* 1996 and 1997 vehicles and 1998 federal-only OBD vehicles did nothave OBD evaporative system leak checks but did have purgesolenoid checks.

### Appendix B