This guide provides a comprehensive overview of the pass/fail criteria for the OBD II (On-Board Diagnostics) test, a crucial component of Smog Check inspections. We’ll also delve into specific instructions for inspecting vehicles known to present challenges during OBD II testing. This information replaces the previous Smog Check OBDII Reference document (Appendix J).
Understanding OBD II Readiness Monitors
The OBD II system in your vehicle performs self-tests called readiness monitors. These monitors verify the proper functioning of emission control components. While most vehicles complete these monitors during regular driving, some may require specific operating conditions that aren’t always met. Occasionally, the owner’s manual will provide guidance on driving procedures to complete these monitors. However, detailed drive cycle information is often only accessible to the Original Equipment Manufacturer (OEM) or within professional automotive repair service literature.
Successfully completing a drive cycle requires the vehicle to experience specific parameters like speed, temperature, pressure, and engine load. Replicating these conditions in typical traffic might be challenging, but they can be achieved using specialized equipment like a dynamometer. Furthermore, monitor completion hinges on fully functional components. A vehicle with underlying mechanical issues may never complete a monitor until a thorough diagnosis and necessary repairs are performed. It’s important to remember that readiness monitors must be run again after events like battery disconnection or replacement of emission-related parts.
The following table outlines the allowable number of incomplete OBD readiness monitors for a vehicle to pass the OBD II portion of a Smog Check inspection:
| Model Year | Fuel Type | Number of Incomplete Monitors Allowed to Pass OBD Test1 |
|---|---|---|
| 1996-1999 | Gasoline2 | Any one3 |
| 2000 and newer | Gasoline2 | Evaporative system3 |
| 1998-2006 | Diesel | Zero |
| 2007 and newer | Diesel | Particulate Filter and Non-Methane HydroCarbon (NMHC)4 |
1 Implemented May 4, 2015.
2 “Gasoline” includes gasoline, propane, and natural gas (CNG, LNG, LPG).
3 The misfire, fuel, and comprehensive component continuous monitors are ignored during an OBD test on “gasoline” vehicles.
4 Implemented July 5, 2023.
OBD II Malfunction Indicator Lamp (MIL) Standards
The Malfunction Indicator Lamp (MIL), often referred to as the “Check Engine” light, plays a vital role in the OBD II test. The following table summarizes the pass/fail standards related to the MIL:
| 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). |
OBD II Communication Standards
Establishing communication between the Obd Ii Trouble Code Scan Tool and the vehicle’s OBD II system is essential for a successful inspection. A communication failure can stem from various reasons, including a damaged OBD II connector or wiring, the presence of aftermarket stereo systems, an incorrect response from the transmission computer instead of the engine computer, or the transmission of invalid data from the vehicle.
| 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 specific OBD addresses that provide information about supported data, MIL status, Diagnostic Trouble Codes (DTCs), and monitor status.
Permanent Diagnostic Trouble Code (PDTC) Standards
Introduced on July 1, 2019, the Permanent Diagnostic Trouble Code (PDTC) check became part of the BAR-OIS Smog Check inspection. PDTCs function similarly to regular DTCs, but they can’t be erased by simply clearing DTCs with a scan tool or disconnecting the battery. The OBD II system will only clear a PDTC after confirming that the previously detected fault is no longer present.
| Model Year | BAR-97/OIS | Standard |
|---|---|---|
| 1996-1999 | BAR-97 | Not applicable. |
| 2000-2009 | OIS | Not applicable. |
| 2010 and newer1 | OIS | Vehicles fail when a PDTC is present.2,3,4,5 |
1 Some 2010 models don’t support PDTCs and are exempt from this check.
2 A stored PDTC will result in failure regardless of MIL status.
3 PDTC presence is ignored if the vehicle has completed at least 15 warm-up cycles and driven over 200 miles since the last OBD information clearing.
4 Certain vehicles have known issues clearing specific PDTCs. These codes are currently ignored by BAR-OIS.
5 Extended warranties, recalls, and repair campaigns address PDTC clearing issues in some vehicles.
Modified Software Standards
Implemented on July 19, 2021, the modified software check aims to identify vehicles with illegally modified software, which will result in a Smog Check failure. Software approved by the California Air Resources Board (CARB) is acceptable. Vehicles failing due to modified software must be restored to OEM-approved or CARB-approved configurations before retesting.
Conclusion
Understanding the various aspects of the OBD II test, including readiness monitors, MIL status, communication protocols, PDTCs, and modified software checks, is crucial for passing a Smog Check inspection. Utilizing an accurate and reliable obd ii trouble code scan tool is essential for diagnosing potential issues and ensuring your vehicle meets the required emission standards. Consult the resources provided for vehicle-specific information and guidance on addressing potential problems.
