### UNITED STATES ENVIRONMENTAL PROTECTION AGENCY ANN ARBOR , MICHIGAN 48105 OFFICE OF AIR AND RADIATION
MEMORANDUM
DATE: March 07,2013
SUBJECT: "Best Practices for Addressing OBD Readiness in IM Testing of Diesel Vehicles Under 14,000 Pounds Gross Vehicle Weight Rating"
FROM: Leila Holmes Cook, Director State Measures and Transportation Planning Center Transportation and Climate Division
TO: Vehicle Inspection and Maintenance (IM) Program Managers and Technical Workgroup Participants

This memo transmits the above-named "Best Practices for Addressing On-Board Diagnostic (OBD) Readiness in IM Testing ofDiesel Vehicles Under 14,001 Pounds (lbs

.) Gross Vehicle Weight Rating (GVWR)" which was prepared primarily by Eastern Research Group (ERG) under contract to U.S. EPA with input from a group of outside experts in the field of on board diagnostics (OBD) testing issues as they apply to light- to medium-duty diesel vehicles. In providing this technical forum EPA was responding to requests for program implementation advice from state IM programs interested in pursuing OBD testing of light- to medium-duty diesel vehicles

. While testing these vehicles is not mandatory, EPA was also responding to concerns expressed by diesel vehic le manufacturers and their representatives that testing such vehicles using EPA's guidance for OBD testing of gasoline-fueled vehicles could lead to high rejection rates of vehicles for having too many unset readiness monitors. The attached document reflects the thinking of the workgroup participants regarding the best way to minimize motorist inconvenience due to readiness-related issues when testing these vehicles

. This document is provided as a courtesy by EPA to interested states to help those who choose to test these vehicles , but should not be construed as an endorsement of such testing , nor as official EPA guidance on the matter.

### Best Practices for Add ress ing On -Board Diagnostic (OBD) Readiness in IM Testing of Diesel Vehicles Under 14,001 Pounds (lbs

.) Gross Vehicle Weight Rating (GVWR) Background Although not required by EPA regulation , a number of state inspection and maintenance (IM) programs are currently performing on-board diagnostic (OBD) tests on model year 1997 (MY 1997) and newer OBD certified light-duty (LD) and medium-duty (MD) diesel vehicles. Some reasons cited by states for testing these vehicles include the following:

• Overall equity, because MY 1996 and newer gasoline vehicles equipped with the same OBD technology are required to be tested in areas which operate IM programs • From a technical standpoint, it seems logical to include these vehicles in the IM program if indeed they are equipped with OBD technolog y . • Although exhaust from newer diesel vehicles contains much less smoke than in the past , it can still be visible at times , and this in tum can lead to the public raising the question as to why these vehicles are not required to be tested

. • Finally , ifOBD testing ofthese vehicles proves viable and the emission benefits can be quantified , there is a possibility that those states with challenging air quality goals will look to include these benefits in future air quality planning projections. However, the issue of credit in state implementation plans is not part of this workgroup ' s charge

.

• Issue Statement: OBD readiness status has been identified as an important component when IM

testing a gasoline-fueled vehicle because it helps ensure that the vehicle ' s emission s ystem is performing properly and also helps in detecting attempts to fraudulently pass an 1M test. Similarly , OBD readiness must be addressed when conducting OBD tests on LD/MD diesel vehicles. However, diesel emission control technology and monitoring strategies differ significantly compared to gasoline vehicles and , therefore , it is not a given that readiness can be treated the same way for these vehicles as for their gasoline-fueled counterparts. Specifically , some diesel OBD monitors , such as the particulate matter (PM) filter monitor, can take much more time to set readiness than comparable gasoline monitors. A gasoline OBD system may typically run all monitors within two weeks , while a diesel OBD system can take eight weeks or more to run all monitors. This is because certain diesel monitors are often linked to PM trap regeneration , and multiple regeneration events may be required to establish readiness. These monitors may include major emission controls such as the PM filter , the NMHC (nonmethane hydrocarbon) catalyst, the oxides of nitrogen (NOx) and selective catalytic reduction (SCR) aftertreatment devices and, in some cases, exhaust sensors. Therefore , using the same readiness criteria (i.e

. , how many monitors can be " not ready " without the vehicle being failed or rejected) as provided for gasoline vehicles may result in an intolerable number of readiness failures for LD and MD diesel vehicles. The diesel readiness criteria recommended by the workgroup to address this issue is described in the sections below. Formation of Workgroup : EPA identified recognized experts in the field of OBD diesel technology. EPA then tasked Eastern Research Group , Inc. (ERG) 1 to convene a workgroup

1 Eas te rn Re se arch G ro up , Inc

. (E RG) EPA co ntract EP- C -11-046 , Wo r k Assign ments 0-10 an d 1-10.comprised of those recognized experts. The purpose of the workgroup was to develop a best practices document (BPD) to address OBD readiness issues for those programs wishing to perform OBD tests on diesel vehicles less than or equal to 14,000 lbs. GVWR. The members of the workgroup are listed in Appendix A. Scope: The scope of this document is limited to MY 1997+ OBD-equipped diesel vehicles less than or equal to 14 , 000 lbs. GVWR. This GVWR range covers LD diesel**(~8 500**  GVWR) and MD diesel (>8 , 500 and**14,000** GVWR). Technical Information There are a number of basic requirements covering various vehicle parameters and test procedures that are already being used for gasoline vehicle inspections that should also be followed in diesel OBD testing. This section provides an overview of typical major elements of an OBD inspection and , where relevant , a comparison between typical diesel and gasoline vehicles with respect to the element. This section is not meant to be an exhaustive list of all elements of an OBD inspection. I

. Diagnostic Trouble Codes (DTCs) : DTCs are used by the OBD system to identify malfunctioning components or systems. Generic fault codes 2 are used for both gasoline OBD systems and diesel OBD systems. Existing IM equipment can read codes from diesel vehicles in the same manner with which they are read from gasoline vehicles.
2

. Permanent Diagnostic Trouble Codes (Permanent-DTCs): Permanent-DTCs are an additional feature that was phased-in on the OBD systems of MY 20 I 0 through 2012 3 gasoline and diesel vehicles. Because this BPD will include recommendations to use Permanent-DTCs when evaluating the readiness status of diesel vehicles so equipped, some background information on Permanent-DTCs is provided below. The primary difference between a Permanent-DTC and a regular DTC is that Permanent-DTCs are stored in memory and cannot be erased with scan tools (generic, aftermarket, or manufacturer-specific) or by disconnecting the battery, but instead can only be erased by the OBD system itself. When the Malfunction Indicator Light (MIL) is commanded " on " in a vehicle that supports Permanent-DTCs , the trouble code is stored as both a regular DTC and also as a Permanent-DTC

. Unlike the regular DTC , the Permanent-DTC is written to non-volatile memory (NVRAM) at the end of the key cycle 4 • Once stored , Permanent-DTCs can only be erased by the OBD s y stem itself in one of two ways.**Fir~t ,**  if a scan tool " code clear " has not been received , the Permanent-DTC will be erased at the same time the MIL turns off(e.g. , ifthe OBD system detects that a fault is no longer present on three consecutive trips , it will extinguish the MIL and erase the Permanent-DTC). Secondly , if a scan tool " code clear " has taken place

2 SAE 12 01 2 3 Note Ti tl e 1 3, Ca li fo rn ia Co de o f Regul ati o n s, S ecti o n 196 8 .2 an d 4 0 CF R Part 8 6.0 0 8 -10 an d 86

. 0 I0

- 2. Beg innin g with MY 20 10 , Perm ane nt-D TCs we re ph ased-in

. Fifty percent o f th e fl eet was requ ired to be Perman ent-D TC co mpliant in MY 2010 ; 7 5 % in MY 20 II , an d I 00 % in MY 2012

. Thi s requireme nt appl ied to bo th the g aso line an d di ese l fl eets. A s can tool compla int wi th S AE J 1979 vers io n May 2007 or newer will be capable of autom at ica ll y dete rmin ing if a ve h ic le s upp orts Permanent-D T C s . 4 NYRAM reta in s its in fo rm ati o n when power is turn ed o ff

. Thi s is in contras t to dyn ami c rand o m access memo ry and stat ic ran do m acce ss me mo ry wh ich bo th retain d ata onl y f o r as lon g as po wer is appli ed

.
2(e.g., techn ician clears code s after repairing a fault) , the Permanent-DTC w ill not be erased until the monitor responsible for setting that specific Permanent-DTC has run at least once and confirmed that the fault is no longer present. The system is designed to be able to store at least four Permanent-DTCs at one time. Should a vehicle have more than one DTC currentl y commanding the MIL on , all of the faults would be stored as Permanent-DTCs and could not be erased until the monitors responsible for each of the Permanent-DTCs has run and confirmed that each of the faults has been corrected. Permanent-DTCs are reported through a different scan tool command (11979 Mode/Service $0A) than regular DTC s, so inspection equipment/ tools can distinguish between the two. Permanent-DTCs have been implemented to make it more difficult for a vehicle owner or technician to clear the fault memory , which can potentially allow the vehicle to pass inspection without being repaired. While readiness monitors were also originall y intended to address this is sue , Permanent-DTCs address many of the shortcomings that have led to the ex isting readine s s policy. Permanent-DTCs also provide a much more direct and accurate indication that an attempt may have been made by a vehicle owner or technician to circumvent the inspection

. Specifically , readiness monitors can be unset for multiple reasons , including those unrelated to a recent emission-related fault , while the presence of a Permanent-DTC provides a definitive indication that the car being inspected previously had the MIL on for that very fault and has not yet re-run that very same diagnostic to determine if the fault is still present. Like unset readine s s , the presence of a Permanent-DTC does not definitively tell y ou ifthe vehicle still has a fault or not so it is appropriate to have s uch cars fail the readiness check until either the Permanent-DTC is erased (because the fault is gone) or the MIL is back on because the fault was re-detected

. Given that Permanent-DTCs are phased in over the 2010 through 2012 model years and that diesel vehicles generally make up a small portion of a vehicle manufacturer ' s fleet , Table 1 was created to generally identify when most diesel vehicles had the feature implemented. However, per 

### J 1979 , scan tools and/or inspection equipment can be designed to automatically determine if a vehicle supports Permanent-DTCs. Use of a scan tool is the more accurate (and preferred) method for making this determination in an inspection program. 

### Table 1: Manufacturer Permanent-DTC Compliance5
Manufacturer MY with full Permanent-DTC Compliance BMW 

### 2012 Cummins 

### 2010 Ford 

### 2012 GM 

### 2012 Mercedes 

### 2012 

## vw 2012

5 On e hundred p erce nt manuf acturer co mplian ce w ith Perman ent-D TC repo rtin g for a ll ve hicl es an d eng ines began with th e 201 2 MY th e co mpl ian ce deadl ine f o r th e ph ase -in p eri o d

. Howeve r, ce rt ified e ng in es .are ofte n in s ta ll e d in veh icles th at are a mode l ye ar newer . The r e f

o re , so me 20 12 me dium-duty veh icles may b e eq uipp ed with 20 II mo de l year engines that may not s upport Perm ane nt-D TCs

. A ll 2013 and later mo de l year me dium-duty ve hi c les s ho uld be e quipped w ith eng in es that s uppo rt Permane nt-D TCs

.
3

### 3. MY coverage: Newer diesel vehicles have been equipped with increasing numbers of emission controls because tailpipe emission standards have become more stringent. Accordingly , more diagnostics have been incorporated into OBD systems to monitor the various controls. While there are various milestones that have occurred over time with respect to what typical emission controls were implemented in what timeframe , the testing options described in this best practices document are designed to apply to all OBD equipped diesel vehicles. 4. Communication protocols: Light duty and medium duty diesel vehicles use the same communication protocols that gasoline vehicles use. Therefore , the existing hardware and software currently in use for gasoline OBD IM testing should also be able to communicate with LD and MD diesel vehicles

. As a point of reference, all MY 2008 and newer diesel vehicles with GVWRs :SI4 , 000 lbs. are equipped with the ISO 15765 Controller Area Network (CAN) communication protocol. 5. OBD readiness monitors: There are 11 readiness monitor bits in a diesel OBD system , which is the same number as in a gasoline OBD system. However , as can be seen in Table 2 , only nine of the eleven bits are actually assigned to monitors at this point. Also, the monitor descriptions are different6 

### from comparable gasoline-fueled vehicles for MY 20 I 0 and newer diesel vehicles, reflecting the fact that the different fuel systems use different emission controls. For example , a state's current vehicle inspection report (VIR) that identifies the 4 1 h 

### monitor as the " Catalyst " in a gasoline vehicle should report the monitor as the " NMHC Catalyst" in a 20 I0 or newer diesel vehicle (the readiness status of both are reported under SAE J1979 Parameter Identification (PID) $01 , Byte D, bit 0) 7 • 

### Per SAE 

### J 1979 , inspection equipment can be designed or updated to use information in the readiness data itself (PID $01 , Byte B , bit 3) to automatically determine whether the gasoline and pre-MY 20 I0 diesel monitor descriptions or the MY 201 0+ diesel monitor descriptions apply to the vehicle. Table 2: Gasoline and Diesel OBD 

### Readiness Monitors
Monitor Readiness Monitor Assignments for all New Readiness Monitor Assignments Number Gasoline and for Diesel through MY 2009 for Diesel from MY 2010+ I 

### Misfire Mi sfire 2 

### Fuel System Fuel System 3 

### Comprehen sive Components Comprehensive Components 4 

### Catalyst NMHC Catal ys t 5 

### Heated Catal yst NOx/SCR Aftertreatment 6 

### Evaporative System (Re served for future) 7 

### Secondary Air Boost Pressure 8 A I C 

### (Reserved for future) 9 02 

### Sensor Exhaust Gas Sensor 10 

### Heated 02 

### Sensor PM Filter II 

### EGRIVVT EGRIVVT

6 SAE J 1979 PID$ 0 I , Data Bytes B ( bit #3), C, and D 7 Fo r a co mp re hen sive lis t of O B D PID s , re f er to SAE J 19 7 9

.
4Also , in a gasoline OBD system , the first three monitors in Table 2 above are considered "continuous " and therefore are always reported as complete and/ or ready. As a result , many states do not include these three monitors as part of the lM readiness evaluation. However, for LD and MD diesels vehicles , only the last of the first three monitors- " comprehensive components "

- is always reported as complete and/or ready. Accordingly , this BPD recommends that IM programs consider all assigned readiness monitors when evaluating the readiness status ofOBD-equipped, LD and MD diesel vehicles.
6

. Diagnostic Link Connector (DLC) , Communications , and DTC Issues: The existing recommendations for gasoline OBD systems with regard to DLC issues such as "missing ," " tampered ," or " malfunctioning DLCs" should be followed for diesel OBD test programs as well. Likewise , "failure to communicate" , pending DTCs , DTCs with no MIL illumination, and/or a MIL commanded on with no DTCs should all be handled in the same way as in the state ' s current gasoline IM program. 7. Fraud Detection: Programs should use the same techniques for detecting "fraud" and

" tampering " as in the state's current gasoline IM program. 8. Individual Monitor Exemptiohs or Requirements : Although not required , many states have found it beneficial to design their inspection software to provide " readiness exceptions " for certain problematic vehicles. Options have included allowing a greater total number of"not ready " monitors (i

.e ., 2 instead of I) and the ability to " ignore " a specific monitor 8 when making the IM readiness determination for a specific vehicle. These exceptions can prevent motorists from having their vehicles rejected for readiness when in reality there is nothing they can reasonably do to bring the vehicle into compliance with the base readiness criteria. Conversely , some IM programs for gasoline-fueled vehicles have required the catalyst monitor to be set to complete for the initial test (and for the re-inspection in cases where the vehicle was initially failed for a catalyst-based DTC). This requirement helps to further protect emission benefits by ensuring that the most important emission control has been monitored and passed at the time of the inspection. Other states have accepted proof of repair in lieu of meeting certain readiness criteria (for example , proof of a catalyst repair in lieu of the catalyst monitor being set to ready for there-inspection)

. These variations can further help to balance motorist inconvenience considerations with the need to ensure that critical emission controls are functioning properly and that components in need of repair have indeed been repaired

. It is recommended that programs that have these types offlexibilities for gasoline vehicles also use them as needed for diesel vehicles, and states should consider including such capabilities in any future software revisions or upgrades.

8 Fo r ex ample , the 199 7 Toyota Terce l and Pase o were un abl e to set th e Ev aporati ve mon itor . Th es e vehicl es we re s ubsequ entl y identifi ed in EPA 's OBD Guidan ce , App endix D

. Th ese ve hic les , and oth ers , are also includ ed in EPA ' s doc um ent entitl ed

" OBD Readin ess Testab ili ty Iss ues " (EPA -420-8-1 2 -044 , Jun e 2012 ) whi ch upd ates an d repl aces th e origi nal App endi x D

.
59. Confirmation of Fuel Type: States should evaluate the effectiveness of their current procedures for identifying vehicle "fuel type" so that gasoline and diesel vehicles are tested based upon the appropriate testing criteria. Methods for confirming vehicle fuel type include enhanced Vehicle Identification Number (YIN) decoding and/or completing additional OBD requests (PID $51, or PID $01 /Byte B/bit3) while scanning the vehicle. 

### LD and MD Diesel IM Readiness Evaluation Recommendation Figure 1 provides a test logic flowchart for performing an IM OBD test on diesel vehicles and is designed to cover OBD equipped diesel vehicles ::; 14 ,000 lbs

. GVWR. The process logic follows the path described below. The recommendations listed in 3a and 3b are those that programs should be able to implement immediately as they do not require software or hardware upgrades to read Permanent-DTCs from newer vehicles. I. Follow all other aspects of inspection protocol prior to readiness evaluation (e.g. visual emission-control inspections and inspection of the MIL status) 9 • 2. If the vehicle supports Permanent-DTCs and the state's IM program equipment can access the Permanent-DTCs , then the Permanent-DTCs should be used in conjunction with readiness monitor status and other criteria such as distance traveled and/or number of warm-ups since the DTCs were cleared to make a readiness determination 10 • 3. If the vehicle does not support Permanent-DTCs or the state's IM program equipment cannot access the Permanent-DTCs, then the procedures below may be implemented 1 1 • However, in cases where the vehicle supports Permanent-DTCs but the state's equipment cannot read them, it should be noted that this method is less robust and should only be used as an interim solution until the IM equipment can be updated because these options will likely lead to relatively greater motorist inconvenience in some cases and reduced emission benefits in other cases.

a. If the vehicle has ::; 1 monitor not read y, then the vehicle passes the readiness determination 12 • lfthe vehicle does not meet this criterion, then move on to the readiness criteria in Step (b) below to provide relief as appropriate to diesel vehicles mapped to the new diesel readiness indicators. b. Use the less stringent readiness monitor criteria of 2 not ready monitors in conjunction with a more rigorous (as compared to #2 above) distance traveled

9 As described in the Background section of this document, diesel vehicles may require additional time compared to gasoline vehicles to set readiness monitors after a repair. To address this difference, this document recommends that vehicle operators be instructed to drive vehicles for two or three weeks after codes are cleared to provide for readiness monitor setting before an in s pection as opposed to the one week that is often used in gasoline applications. 10 The term s " fail readiness determination " or " fail readiness check " are used here and throughout this document to refer to a vehicle that does not meet a given set of readiness criteria

. The final 1M test outcome for such vehicles can vary on a state-by

state basis depending on their regulatory requirements and each state should proceed accordingly to fail for readiness , reject from testing , etc. 1 1 This is the path described below in #2 " No use ofPermanent-DTCs and**I** unset monitors ". 12 Thi s is the current readiness criteria used for gasoline vehicles.

6and/or number of warm-ups since the DTCs were cleared if supported 13 • ln order to pass readiness in this step , both of the unset readiness monitors must be within the categories of PM Filter, NOx/SCR aftertreatment or NMHC Catalyst for vehicles mapped to the new diesel readiness indicators (i.e. , MY 20 I 0 + diesel vehicles), and within the categories of Catalyst, Heated Catalyst, or 

### 02 Heater for those that are not. The requirement that a minimum distance be traveled or a minimum number of warm-ups occur since the last time a vehicle ' s OBD codes were cleared (both of which can be read directly by technicians with a scan tool) 14 can best be communicated to individual drivers that fail to meet these criteria in terms of their needing to operate the vehicle normally for a prescribed minimum amount oftime before returning for re-inspection. ln the options outlined below , the workgroup has recommended two or three weeks as a good initial starting point for the paths outlined in Figure 1 , however, each state has the discretion to modif y these time s following consultation with EPA. These options and associated paths are outlined in Figure 1 and described in more detail below

. I. Use of Permanent-DTCs (right-hand side of Figure I)
It s hould be noted that implementing the recommendations of this document , including using Permanent-DTC s, will likely require revision to current IM inspection software and associated databases. For e x ample , the 1M scan tool will need to use a different command to read Permanent-DTCs ; the electronic inspection record will need to be revised to include PermanentDTC related data ; the IM database must be adapted to store the additional data; and s ome state s may even change the program ' s vehicle inspection report (VIR) to identify the presence of a Permanent-DTC as the cause ofthe IM failure. Full implementation ofthe recommendations will likely vary from state to state as individual states will need to take into account their current contract structure and timing , equipment capability , and even associated regulatory changes necessary to identif y the criteria in regulation. However, as noted above , interim implementations that do not use Permanent-DTCs will be less effecti ve and likely have increased motorist inconvenience for some vehicles. The Permanent-DTC option is illustrated on the right side of Figure I with the key decision blocks colored in blue. If a vehicle is presented for testing and the MIL is not commanded on , the scan tool will query the OBD system to determine if the vehicle supports Permanent-DTC technology. If it does , and there are Permanent-DTCs stored , then the vehicle should be checked to see if it has any known testability issues

. If it does not , then the vehicle will fail the readine s s check (unless the vehicle has a known testability issue that would make the failure determination inappropriate at this point).

13 l fthe s can too l or ve hi c le software does no t s up po rt checkin g mil es trave led an d numb e r of warm-up cyc les sin ce code cl eari ng, th en th e ve h ic le may al so p ass th e readin ess dete rmination at th e s tate ' s di sc reti o n. 14 Th is information is s tored in PID s $3 0 and $ 3 1

. Te mp orary di sco nn ect ion of th e b attery may cau se th ese co unters to reset to zero . Vehicl es w ith mul tipl e co ntro ll ers may repo rt di ffe re nt v alue s f or th e numb er of w arm-up cycl es and di s tan ce tr ave led

. In s uch cases , the mini mum valu es repo rted sho uld be u se d to dete rmin e i f the reco mm ended target va lu es fo r these param eters have bee n me t. These reco mm end ed targe ts are di scu ssed in more d etail be low.

7If the vehicle supports Permanent-DTCs and there are no Permanent-DTCs stored, there is higher confidence that the vehicle likely does not have an unrepaired fault. There is no recommended limitation on the types of2 or fewer incomplete readiness monitors 15 in the second blue decision block to determine whether to check the vehicle for known testability issues or move to the next blue dec ision block checking for I or 0 incomplete readiness monitors. While the absence of a stored Permanent-DTC does greatl y increase the confidence that the vehicle does not have an unrepaired fault present , there are still a few scenarios where faults could be present without a Permanent-DTC stored (e

. g ., a recent retlash or reprogramming ofthe vehicle , or multiple sequentially monitored components that have failed but have been disabled due to the first fault 16). As such , readiness monitors are still us ed as a backstop to help address this concern in the third blue decision block, where , if the vehicle has one or fewer unset readiness monitors , then it should pass the readiness determination. If there are two unset readiness monitors , then in the fourth blue decision block it is determined if the distance since the last code clear is more than 500 miles 17 and if the number of warm-ups s ince code clear (WU-SCC) is greater than thirty 18 • If both of these criteria are met, then the vehicle should pass the readiness determination. If not, the process should proceed to the fifth blue decision block , where it is determined ifthe vehicle has known testability issues Thi s will require programs to track and tabulate those specific vehicles (i.e. Make/Model/MY , YIN strings) that have demonstrated repeated known readiness problems. The workgroup recommends such a list be compiled and maintained by a group of states performing OBD diesel te sting in consultation with EPA. The list could be distributed through posting on the OBD Clearinghouse web site and at the IM Solutions Conference or other public forums. 2

. No use ofPermanent-DTCs and < I unset monitors Cleft-hand side of Figure 1) If a diesel vehicle does not support Permanent-DTC technology (or if a program ' s 1M scan tools cannot request Mode $0A data) , then a readiness criteria of S l unset monitor is recommended. This is the first green decision block to the left of Figure 1. Although many MY 2009 and newer diesel vehicles may have difficulty meeting the current gasoline readiness criteria of one or fewer unset readiness monitors if codes were recently cleared , some may be able to pass this criterion and if the y can it is recommended that the y pass the readiness check.

15 The less stri nge nt cr iteri o n of any 2 was chose n becau se the di ese l Perrn ane nt-D TC p ath in the test log ic fl owchart is a more s t

ri nge nt test th an th e o th er optio n d esc rib ed be low . Th e o th er opti o n re qui res more stri nge nt dis tance an d warm-up criteri a. 16 W ith most OBD syste ms , re levan t mo nitors m ay beco me di sabl ed upo n detec tion o f a fa ult with o ne o r more rela ted co mp o nents. If th e ve h ic le owne r ig nored th e detected fault f or a s ub s tan t ia l pe riod o f time, o th er co mpo ne nts could have sub sequ entl y m alfun c ti o ned but wi ll no t be mo nito red until th e first m alfun cti o n has bee n re paire d. Th ere fore, requirin g s om e o r all read i n ess mon itors to be co mpl ete wi ll in cre ase th e like lihood th at th e ve h ic le is no t i n a co nditi on to tri gger a "ch a in " of success ive fau lts afte r th e fir s t o ne is fi nall y repaired

. 17 Th is fi gure is b ased o n an es tim ated annual dri vin g d is tan ce of 12 , 00 0, o r I ,000 miles per mo nth

. There f ore, it is an tic ip at ed a ve h ic le wi ll be dri ve n o n ave rage about 500 mil es in two weeks and 7 5 0 mil es in th ree weeks. The ve hi c le owner shou ld be ins tru cte d th at norm a l ope rati o n o n both city and hi ghway routes is mos t effect ive i n settin g read iness mo nitors . 18 Th e va lu e of30 warm -u p cyc les is b ased o n an ass umed ave rage of2 warm - up cycles pe r day o r 14 per week

. Th e wo rkgro up reco mm end s using 30 warm -up cyc les to represe nt an average fo r a two week pe ri o d an d 45 warm - up cyc les f or a three week perio d

.
8If the number of unset monitors is greater than one, the vehicle moves to the first yellow decision block where if there are three or more unset monitors of any type the vehicle should fail the readiness check. However, if there are two unset monitors and both are for monitored controls that are known to be difficult to set (i

.e., the PM Filter, NOx/SCR after-treatment, or NMHC catalyst), then in the second yellow decision block it is determined if more than 750 miles have been driven and at least 45 warm-up cycles have occurred since the last code clear 1 9 • If these conditions are met then the vehicle should pass the readiness determination. If the scan tool or vehicle software does not support checking miles traveled and number of warm-up cycles since code clearing, then the vehicle may also pass the readiness determination at the state's discretion. Otherwise, the vehicle should fail the readiness check. The criteria in this scenario are more stringent than in the case where Permanent-DTCs are supported primarily because of the higher confidence the absence ofPermanent-DTCs provides in assessing whether the vehicle has an emissions related problem. Furthermore, older vehicles that do not support Permanent-DTCs typically have fewer readiness monitors. Therefore, it is appropriate to further limit which monitors can be incomplete and to require additional vehicle operation time since the last code clear to help ensure that fault codes have not been erased without the owner having performed the necessary repairs.

19 The value of2 unset monitors among this group was chosen based on an analysis of existing data from Massachusetts that demonstrated using 2 unset monitors (regardless of which ones they were) instead of I resulted in LDD vehicle Make/Model categories with initial not ready rates in the range of0-9%

. Using the :S I criteria resulted in initial not ready rates in the range of 0-13%. The overall MD diesel vehicle initial not ready rate fell from 7% to 3% with the ::::2 criteria

. This analysis is based on 5 , 817 LD diesel and 3,232 MD diesel vehicle initial OBD tests performed in Massachusetts on MY 2010-2012 collected in 2010- 2012

. It is recommended that similar analyses be performed as additional OBD diesel data becomes available to confirm the validity of these criteria or provide information that will support adjusting the criteria accordingly

.
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### Appendix A: Workgroup Members The workgroup members are listed below. State: California Air Resources Board- Mike McCarthy , Allen Lyons Massachusetts Department of the Environment- Craig Woleader, Julie Ross , Paul Davis New Jersey Department of Environmental Protection- Bill Etherington, Tom Dvorak New York Department of Environmental Conservation- Jim Clyne , Greg English Utah Department of Env ironmental Protection- Joe Thomas , Chris Woodhave Industry: Cummins- Mark Stepper, Robert Weiss , Greg Pataky Ford- Ken McAlinden General Motors- Dave Ferris, Chris Brown Volkswagen- Bob Gruszczynski, Volker Lantzsch BMW- Carl Heinz Bayer, Edwin Bachhelm Mercedes- Ashim Manchanda Associations: Auto Alliance- Steve Douglas Engine Manufacturers Association- Lisa Stegink Environmental Protection Agency: Office of Transportation and Air Quality- Patty Klavon , Dave Sosnowski
Contractor: Eastern Research Group- Mike Sabisch , Diane Preusse , Jim Lindner

A-I 

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### Appendix B: Known Testability 

### Issues
The EPA guidance document "Performing Onboard Diagnostic System Checks as Part of a Vehicle IM Program " released in June 2001 contained an appendi x (Appendix D) that identified those gasoline vehicles by Make/Model/MY that were known to have difficulty setting readiness or may never set certain readiness monitors. The purpose of Appendix D was to alert IM programs that these vehicles should be handled differently with regard to the readiness criteria when presented for an OBD test. Flexibility was given to states to perform an idle or two-speed idle test on these vehicles or perform an OBD test with less than the required number of set readiness monitors. Since 200 I , EPA has updated Appendix D to include additional vehicles that have been identified with readiness issues

. In January 2008 the "IM OBD Vehicle Readiness Exception List " was released , and then in June of20 12 the " OBD Readiness Testability Issues " document was published. Although at this time there is not such a list for diesel vehicles ::; 14,000 lbs

. GVWR, some vehicles may be identified with OBD readiness testability issues after the procedure described in this document and outlined in Figure I have been implemented. There is one " Known Testability Issues? " decision block in Figure I as a part of the readiness determination protocol (one path of which includes the use of Permanent-DTCs). Two example issues are listed below; however, these are only provided for informational purposes so that states can be made aware of the type of issues that could arise that are unique to diesel vehicles

. As stated earlier in the body ofthis document , the workgroup recommends that a Known Testability Issues document be maintained by the states and shared through the OBD Clearinghouse and IM Solutions.

• Example I: If the readiness check failed due to the presence of stored PermanentDTC(s) (right-hand side ofFigure I path):
If Permanent-DTCs are being utilized as part of the readiness determination protocol, the process will fail any vehicle that has one or more permanent DTCs present. This is true even if the vehicle has met the readiness criteria. Permanent-DTCs that have dependencies on PM trap regeneration or that have environmental dependencies (such as ambient temperature) may take a long time to clear after a repair has been made and DTCs cleared. Some examples may include PM filter diagnostics, NHMC catalyst diagnostics , PM and NOx sensor diagnostics , NOx catalyst diagnostics, DEF heater diagnostics , and HC doser diagnostics. If this condition occurs , it may be challenging for the driver to get such Permanent-DTCs to clear , possibly taking significantly longer than three weeks of driving in order for the vehicle to accrue sufficient mileage or see the proper environmental conditions (e.g , the proper seasonal conditions) for the monitors to run. Vehicles with these types of issues or other types of issues associated with failing readiness due to Permanent-DTCs could be included in a Known Testability Issue document.

B-1• Example 2: If the readiness check failed due to the number of incomplete monitors , having two incomplete monitors of the incorrect type, or insufficient distance or number of warm-ups since code clear (left hand side of Figure 1 path) : Some vehicles may have more than two readiness monitors that are difficult to set because of dependencies on PM trap regeneration or on operational conditions (such as ambient temperature). For example , certain vehicles may have difficulty setting all three monitors listed in Footnote 2 of Figure 1, or perhaps have difficulty setting monitors not listed in Footnote 2. Vehicles with these types of issues or other types of issues associated with failing readiness due to the number of incomplete monitors , having two incomplete monitors of the incorrect type , or insufficient distance or number of warm-ups since code clear could be included in a Known Testability Issue document.

B-2