As a content creator for carparteu.com and an automotive repair expert, I’ve compiled this comprehensive Obd2 Reference Guide. Expanding on the original document, this guide is tailored for English-speaking automotive professionals and enthusiasts seeking in-depth knowledge of On-Board Diagnostic systems. We’ll delve into OBD2 testing standards, common issues, and practical solutions, ensuring you’re equipped to navigate the complexities of modern vehicle diagnostics.
Understanding OBD-II Smog Check Standards
The On-Board Diagnostic (OBD) system is crucial for monitoring vehicle emissions and overall engine health. For smog check inspections and effective vehicle repair, understanding the pass/fail criteria is essential. Let’s break down the key standards.
Readiness Monitor Standards
Readiness monitors are self-tests performed by your vehicle’s OBD system to confirm that emission control systems are functioning correctly. These monitors need to be completed for a vehicle to pass the OBD portion of a smog check. While many vehicles set these monitors during normal driving, some require specific driving conditions, often detailed in OEM service literature or repair industry guides. Factors like speed, temperature, and engine load are critical for monitor completion. Furthermore, properly functioning components are a prerequisite; a faulty sensor or system may prevent a monitor from ever becoming ready until diagnosed and repaired. After any repair that involves disconnecting the battery or replacing emission components, readiness monitors will reset and need to be rerun.
The number of incomplete readiness monitors allowed varies by model year and fuel type, as outlined below:
| Model Year | Fuel Type | Number of Incomplete Monitors Allowed to Pass OBD Test¹ |
|---|---|---|
| 1996-1999 | Gas² | Any one³ |
| 2000 and newer | Gas² | Evaporative system³ |
| 1998-2006 | Diesel | Zero |
| 2007 and newer | Diesel | Particulate Filter and Non-Methane HydroCarbon (NMHC)⁴ |
¹ Implemented May 4, 2015.
² “Gas” includes gasoline, propane, natural gas (CNG, LNG, LPG).
³ The misfire, fuel, and comprehensive component continuous monitors are disregarded during an OBD test on “gas” vehicles.
⁴ Implemented July 5, 2023.
Understanding these standards is crucial for ensuring vehicles meet emission requirements. For gasoline vehicles from 2000 onwards, only the evaporative system monitor can be incomplete. For newer diesels, the particulate filter and NMHC monitors are the exceptions.
Malfunction Indicator Lamp (MIL) Standards
The Malfunction Indicator Lamp (MIL), often called the “Check Engine” light, is a primary indicator of potential emission control issues. Its behavior during a smog check is strictly regulated:
| Vehicle | Pass/Fail | Standard |
|---|---|---|
| All with OBDII | Pass | MIL illuminates when key on engine off (KOEO). |
| All with OBDII | Pass | MIL turns off when engine running (KOER). |
| All with OBDII | Fail | MIL does not illuminate when key on engine off (KOEO). |
| All with OBDII | Fail | MIL illuminates when engine running (KOER). |
Alt text: Diagram illustrating the correct Malfunction Indicator Lamp (MIL) operation for OBDII testing: MIL on during Key On Engine Off (KOEO) and MIL off during Key On Engine Running (KOER), indicating passing conditions.
The MIL should illuminate briefly when the ignition is turned on but the engine is not running (KOEO) to confirm the bulb is functional. Once the engine starts (KOER), the MIL should turn off if no emission faults are detected. Failure in either of these scenarios results in a smog check failure.
Communication Standards
Successful communication between the diagnostic tool and the vehicle’s OBD system is fundamental for any OBD test. Communication failure can stem from various sources, including a faulty OBD connector, wiring problems, aftermarket stereo installations interfering with the system, or even the vehicle’s computer sending incorrect data.
Here are the communication standards for OBD testing:
| Vehicle | BAR-97/OIS | Standard |
|---|---|---|
| All with OBDII | BAR-97 | Vehicle communicates with BAR-97. |
| All with OBDII | OIS | Vehicle communicates with OIS and transmits required data.¹ |
¹ Required data typically includes data from OBD addresses: Mode $01 PID $00, Mode $01 PID $01. Mode $01 PID $00 returns supported data on the vehicle. Mode $01 PID $01 returns MIL status, diagnostic trouble codes (DTCs), and monitor status.
For a vehicle to pass the OBD communication portion of a smog check, it must successfully communicate with the testing equipment and transmit the necessary data. This data includes essential parameters like supported PIDs, MIL status, DTCs, and monitor status, crucial for a complete and accurate inspection.
Permanent Diagnostic Trouble Code (PDTC) Standards
Permanent Diagnostic Trouble Codes (PDTCs) were introduced to prevent clearing of emission-related codes before a vehicle has been properly repaired and re-tested. Unlike regular DTCs, PDTCs cannot be erased using a scan tool or by disconnecting the battery. They are automatically cleared by the OBD II system only after the system verifies that the original fault is no longer present.
Since July 1, 2019, PDTC checks have been incorporated into smog inspections:
| Model Year | BAR-97/OIS | Standard |
|---|---|---|
| 1996-1999 | BAR-97 | Not applicable. |
| 2000-2009 | OIS | Not applicable. |
| 2010 and newer ¹ | OIS | Vehicles fail when a PDTC is present. ²,³,⁴,⁵ |
¹ Some 2010 vehicles may not support PDTCs and are exempt from this check.
² A vehicle with a stored PDTC fails regardless of the MIL status (on or off).
³ PDTC presence is ignored if the vehicle has completed at least 15 warm-up cycles and 200 miles since the last OBD data clear (verified by Mode $01 PID $30 and $31).
⁴ Certain vehicles with PDTC clearing issues are recognized by BAR-OIS, and these codes may be ignored. Refer to the Permanent Diagnostic Trouble Code Vehicles of Interest section for more details.
⁵ Extended warranties, recalls, and repair campaigns exist for some vehicles struggling to clear PDTCs. These are listed under Permanent Diagnostic Trouble Code Vehicles of Interest. For PDTC-related failures on these vehicles, advise the owner to consult their dealer for repairs covered under warranty.
A vehicle will fail a smog check if a PDTC is present, even if the check engine light is off. However, there are exceptions. PDTCs may be ignored if the vehicle has completed a significant number of warm-up cycles and miles since the last code clear, indicating sufficient time for self-correction. Additionally, some known vehicle-specific PDTC issues are bypassed by the BAR-OIS system.
Modified Software Standards
To ensure vehicles meet original emission standards, checks for modified software were introduced on July 19, 2021. Software modifications not approved by the California Air Resources Board (CARB) are considered illegal and will cause a vehicle to fail a smog check.
Vehicles with detected illegal software modifications will fail the inspection, with “Modified Software” noted on the vehicle inspection report. To pass a subsequent inspection, the vehicle must be restored to an OEM-approved or CARB-approved software configuration. Retesting can be done at any licensed Smog Check station unless otherwise directed to a Referee or STAR station. Consumers disputing results can contact the Smog Check Referee.
Troubleshooting OBD-II Test Failures: Vehicles of Interest
Certain vehicle makes and models are known to exhibit specific issues during OBD testing. These issues can range from communication problems to incomplete readiness monitors or false MIL illumination. The following sections detail these “Vehicles of Interest,” providing insights into causes, remedies, and inspection instructions.
OIS Vehicles of Interest
This section focuses on gasoline, flex-fuel (model year 2000 and newer), and diesel (model year 1998 and newer) vehicles known to have pattern issues with the OBD test portion of an OIS inspection.
| Make | Year | Model Engine (L); Fuel Type | Issue | Cause and Possible Remedy | Instruction to Inspector |
|---|---|---|---|---|---|
| Audi | 2000-2004 | A4 & A6 | Fail for no OBD communication. No response or Only Transmission Control Module responds to DADs requests. ABS and/or brake lamp illuminated in instrument panel cluster. | Broken ground bond wire in ABS module causes diagnostic communication issues with the ABS module, ECM, and TCM. Diagnose and repair per Audi TSB #A45-15-10. | Likely broken vehicle. Repair and retest. |
| BMW | 6/1/99 – 7/31/00 | 323i Sedan | May not pass inspection due to oxygen sensors readiness monitor not set/not fitted/not supported. | DME Software error. Reprogram DME with the updated software. | Check the DME “programmed control unit” number listed in TSB #SI B12 16 16 and follow TSB instructions. |
| Chevrolet | 2019 | Express 2.8L (diesel) [California certified] | Exhaust Gas Sensor monitor will not complete. A Particulate Matter sensor fault may not set DTC or illuminate MIL. | The Engine Control Module (ECM) may not properly handle diagnostic information for the exhaust Particulate Matter (PM) sensor. Dealers are to reprogram the ECM per Emission Recall N232408230. | Vehicle requires reflash. Perform recall then retest. |
| Chrysler | 2003 | PT Cruiser 2.4 liter DOHC 16v turbocharged (sales code EDV) with 5- spd manual G288 trans (sales code DDD) | Failure to set catalyst monitor. | PCM software error. Dealer must reprogram PCM. Emissions warranty extended to lifetime for this issue. Diagnose and repair per TSB #18-112-16. Possible repair payment reimbursement, see warranty D-16-26. | Vehicle requires reflash. Repair per TSB and retest. |
| Dodge/Ram | 2010-2015 | 2500 & 3500 6.7L (diesel) [California certified] | NOx after-treatment monitor will not complete. | Vehicle design anomaly. | Test normally. BAR-OIS temporarily allows NOx after-treatment monitor to be incomplete until vehicle manufacturer remedy is available. |
| Ford | 2020-2022 | Escape; all engines; Gasoline and hybrid | Might not communicate with BAR-OIS. | Design issue. Software update available. | Test normally. If the vehicle you are inspecting fails the OBD test for no communication, direct the vehicle to a Ford dealership for a software update. Issue may be due to software in gateway module—see SSM 50974. Similar messaging will be displayed on the OIS during the inspection, and printed on the VIR for consumers. |
| Jaguar | 2017-2019 | Jaguar XE, XF, & F-Pace 2.0L (diesel) [California certified] Test Group HJLXJ02.0STY, JJLXJ02.0STY, KJLXJ02.0STY | NOx Aftertreatment System monitor will not complete. | Vehicle design anomaly. Dealer issued recall H444. | Test normally. If the vehicle you are inspecting fails the OBD test for incomplete NOx aftertreatment monitor, direct the vehicle to a Jaguar dealership for a software update. |
| Land Rover | 2017-2019 | Discovery, Range Rover, Range Rover Sport, Velar 2.0L & 3.0L (diesel)[California certified] Test group HJLXT03.0GTR, JJLXJ02.0STY, KJLXJ02.0STY | NOx Aftertreatment System monitor will not complete. | Vehicle design anomaly. Dealer issued recall N808. | Test normally. If the vehicle you are inspecting fails the OBD test for incomplete NOx aftertreatment monitor, direct the vehicle to a Land Rover dealership for a software update. |
| Lincoln | 2020-2022 | Corsair; all engines; Gasoline and hybrid | Might not communicate with BAR-OIS. | Design issue. Software update available. | Test normally. If the vehicle you are inspecting fails the OBD test for no communication, direct the vehicle to a Ford dealership for a software update. Issue may be due to software in gateway module—see SSM 50974. Similar messaging will be displayed on the OIS during the inspection, and printed on the VIR for consumers. |
Alt text: Excerpt from the OIS Vehicles of Interest table, focusing on Audi, BMW, Chevrolet, Chrysler, Dodge/Ram, Ford, Jaguar, Land Rover, and Lincoln, illustrating common OBD communication and readiness monitor issues for specific models and years.
This table provides a snapshot of vehicles with known OBD-II related issues. For example, certain Audi and VW models from the early 2000s may fail due to communication issues caused by a broken ground wire in the ABS module. Similarly, various Ford, Lincoln, and Jaguar/Land Rover models are listed due to potential communication problems or incomplete NOx aftertreatment monitors, often requiring software updates or dealer intervention. Inspectors should consult this table when encountering OBD test failures, as it may point to known vehicle-specific issues and pre-approved remedies. Always refer to the ‘Instruction to Inspector’ column for guidance on handling these specific cases.
PDTC Vehicles of Interest
This section lists vehicles known to have issues with Permanent Diagnostic Trouble Codes (PDTCs) that may not clear as expected.
| Make | Year | Model Engine (L); Fuel Type | Issue | Cause and Possible Remedy | Instructions to Inspector |
|---|---|---|---|---|---|
| Audi | 2010-2012 | Q7; 3.0 (TDI/diesel) | Permanent Fault Codes P0087, P0088, P053F, P064A, P2635, and P0230 will not clear if present. | No remedy is available. | Test normally. BAR-OIS ignores these codes. |
| Chrysler | 2011-2015 | 200, 300, Town and Country; 2.4, 3.6, 5.7, 6.4 | Permanent Fault Codes will not clear. | Reflash per Recall V51. | Reflash then retest. |
| Dodge | 2011-2015 | Avenger, Caliber, Challenger, Charger, Grand Caravan, Dakota, Dart, Durango, Journey, Nitro; Various Engines | Permanent Fault Codes will not clear. | Reflash per Recall V51. | Reflash then retest. |
| Ford | 2011-2014 | Mustang; 3.7 & 5.0 (gasoline) | Vehicle fails for Permanent Fault Code P0315. | Vehicle not self-clearing permanent fault code. | Refer the motorist to Ford for Customer Satisfaction Program 17N01. |
| Freightliner/Mercedes | 2014-2015 | Sprinter 2500 Sprinter 3500 (diesel) | Vehicle fails for Permanent Fault Codes P202A, P203A, P208A, P20B9, P20BD, P20BE or P20FA. | Vehicle not self-clearing permanent fault code. | Test normally. BAR-OIS will ignore these codes. |
| Jeep | 2010-2017 | Commander, Grand Cherokee, Liberty, Patriot / Compass, Wrangler, Cherokee (diesel); Various Engines | Permanent Fault Codes will not clear. | Reflash per Recall V51. | Reflash then retest. |
| Ram | 2010-2017 | 1500, 2500, 3500, Promaster; Various Engines | Permanent Fault Codes will not clear. | Reflash per Recall V51. | Reflash then retest. |
| Volkswagen | 2010-2012 | Touareg; 3.0 (TDI/diesel) | Permanent Fault Codes P20B5, P0087, P0088, and P053F will not clear if present. | No remedy is available. | Test normally. BAR-OIS ignores these codes. |
Alt text: Partial view of the PDTC Vehicles of Interest table, highlighting Audi, Chrysler, Dodge, Ford, Freightliner/Mercedes, Jeep, Ram, and Volkswagen, and detailing common Permanent Diagnostic Trouble Code (PDTC) issues and recommended actions for inspectors.
This table highlights vehicles where certain PDTCs are known to persist, even after the underlying issue has been resolved. For instance, several Chrysler, Dodge, Jeep, and Ram models from the early to mid-2010s may exhibit PDTCs that require a PCM reflash to clear, as indicated by Recall V51. Conversely, for certain Audi, Volkswagen, and Mercedes/Freightliner models, specific PDTCs are recognized as non-clearing design anomalies and are therefore ignored by the BAR-OIS system during inspection. Inspectors should be aware of these vehicle-specific PDTC behaviors to avoid unnecessary repair referrals when the system is designed to bypass these known issues.
BAR-97 EIS Vehicles of Interest
For older vehicles (model year 1996-1999) undergoing BAR-97 EIS inspections, monitor readiness issues are sometimes encountered due to vehicle design or software limitations. In many cases, the BAR-97 EIS system is programmed to accommodate these anomalies.
| Make | Year | Model Engine (L); Fuel Type | Issue | Cause and Possible Remedy | Instructions to Inspector |
|---|---|---|---|---|---|
| BMW | 1996 | 7-Series, 8-Series 5.0L, 5.4L | Monitors difficult to complete. | EIS ignores readiness status. | |
| Chrysler | 1996 | Cirrus, Concord, LHS Sebring Convertible | All monitors reset to incomplete upon every ignition key-off. | Recall campaign #678 applies to California certified vehicles originally sold in California. TSB #18-005-01 (with lifetime warranty) applies to federal certified and California certified originally sold in northeast states. | Comply with recall, then test as normal. |
| Dodge | 1996 | Stratus, Intrepid, Neon | All monitors reset to incomplete upon every ignition key-off. | Recall campaign #678 applies to California certified vehicles originally sold in California. TSB #18-005-01 (with lifetime warranty) applies to federal certified and California certified originally sold in northeast states. | Comply with recall, then test as normal. |
| Eagle | 1996 | Vision | All monitors reset to incomplete upon every ignition key-off. | Recall campaign #678 applies to California certified vehicles originally sold in California. TSB #18-005-01 (with lifetime warranty) applies to federal certified and California certified originally sold in northeast states. | Comply with TSB, then test as normal. |
| Hyundai | 1996-1998 | Accent 1.5L Elantra 1.8L Sonata 2.0L, 3.0L | Monitors difficult to complete. | EIS ignores readiness status. | |
| Infiniti | 1996 | All models | Catalyst and evaporative system monitors are difficult to complete. | Follow drive cycle for specific vehicle model per TSB #ITB98-011F, June 7, 2013. | Test as normal. |
| Kia | 1996 | Sephia Sportage | Monitors difficult to complete. | EIS ignores readiness status. | |
| Lexus/Toyota | 1996-1999 | All models | Monitors can be difficult to complete. | Follow drive cycles in Lexus/Toyota service information. | Test as normal. |
| Mitsubishi | 1996-1999 | All Models | Monitors difficult to complete. | EIS ignores readiness status. | |
| Nissan | 1996 | Sentra 1.6L and 2.0L manual, 200SX 1.6L, 240SX 2.4L, Maxima 3.0L, Pickup 2.4L | Monitors difficult to complete. | EIS ignores readiness status. | |
| Plymouth | 1996 | Breeze, Neon | All monitors reset to incomplete upon every ignition key-off. | Recall campaign #678 applies to California certified vehicles originally sold in California. TSB #18-005-01 (with lifetime warranty) applies to federal certified and California certified originally sold in northeast states. | Comply with recall, then test as normal. |
| Saab/Volvo | 1996-1998 | 900 2.3L, All models | Monitors difficult to complete. | EIS ignores readiness status. | |
| Subaru | 1996 | All models | Readiness cleared at key-off. | EIS ignores readiness status. |
Alt text: Excerpt from the BAR-97 EIS Vehicles of Interest table, showcasing BMW, Chrysler, Dodge, Eagle, Hyundai, Infiniti, Kia, Lexus/Toyota, Mitsubishi, Nissan, Plymouth, Saab/Volvo, and Subaru models from 1996-1999, with a focus on monitor readiness issues and the EIS system’s handling of these issues.
For these older models, monitor completion can be challenging. As the table indicates, for many 1996-1998 vehicles across different manufacturers like BMW, Chrysler, Hyundai, Kia, Mitsubishi, Nissan, Saab, Subaru, and Volvo, the EIS system is designed to disregard readiness status due to inherent difficulties in setting monitors. For specific Chrysler, Dodge, Eagle, and Plymouth models from 1996, a recall (#678) and TSB (#18-005-01) were issued to address the issue of monitors resetting upon key-off, although the EIS system also accommodates this by ignoring readiness status if the repair is not performed.
Conclusion
This OBD2 reference guide provides a detailed overview of OBD-II smog check standards and highlights common vehicle-specific issues that can arise during testing. Understanding these standards and being aware of “Vehicles of Interest” is crucial for automotive technicians and smog check inspectors. By using this guide, professionals can more accurately diagnose OBD-related issues, apply appropriate remedies, and ensure vehicles meet emission compliance. Staying informed about OBD2 systems and their nuances is essential for efficient and effective vehicle repair and maintenance in the modern automotive landscape. This guide serves as a valuable resource to navigate the complexities of OBD2 testing and troubleshooting.
