Readiness monitors, communication protocols, and diagnostic trouble codes (DTCs), including permanent DTCs (PDTCs), are essential aspects of a vehicle’s On-Board Diagnostics (OBD) system. This article provides a comprehensive guide to understanding these components and addressing common issues that may arise during a Smog Check inspection. Understanding how these systems work can help car owners troubleshoot problems and ensure their vehicles pass emissions tests. While disabling OBD2 codes might seem like a solution to a failed emissions test, it’s crucial to understand that this is not a recommended practice. Addressing the underlying issue causing the code is the correct approach. This article will focus on understanding the reasons behind OBD2 codes and how to properly address them.
Understanding OBD2 Readiness Monitors
Readiness monitors are self-tests conducted by the OBD system to evaluate the performance of emission control components. Successful completion of these monitors is crucial for passing an OBD test during a Smog Check. However, certain driving conditions or vehicle designs might hinder the completion of these monitors. While some owner’s manuals offer guidance on driving cycles to facilitate monitor completion, detailed information is often exclusive to Original Equipment Manufacturers (OEMs) or available in specialized repair manuals.
Driving cycles involve specific operating parameters such as speed, temperature, pressure, and engine load, which can be challenging to replicate in regular traffic. Dynamometer equipment might be necessary in such cases. Furthermore, proper functioning of vehicle components is paramount for monitor completion. A thorough diagnosis and repair of any faulty components might be required before a monitor can run successfully. Activities like disconnecting the vehicle’s battery or replacing emission components necessitate rerunning the readiness monitors.
The table below outlines the permissible number of incomplete OBD readiness monitors for passing a Smog Check inspection based on the vehicle’s model year and fuel type.
| 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 ignored during an OBD test on “gas” vehicles.
4 Implemented July 5, 2023.
Malfunction Indicator Lamp (MIL) and Communication Standards
The Malfunction Indicator Lamp (MIL), commonly known as the “Check Engine” light, plays a critical role in indicating emission-related problems. Specific pass/fail criteria related to the MIL are implemented during BAR-97 and OIS inspections. The MIL should illuminate when the ignition is on and the engine is off (KOEO) and turn off when the engine is running (KOER). Failure to adhere to these standards results in an automatic fail.
Effective communication between the vehicle and the testing equipment is vital for a successful OBD test. A communication failure can stem from various factors, including a damaged OBD connector, wiring issues, aftermarket stereo installations, or invalid data transmission. For BAR-97 inspections, communication with the BAR-97 system is mandatory. OIS inspections require communication with the OIS and the transmission of specific data points, such as MIL status, DTCs, and monitor status.
Permanent Diagnostic Trouble Codes (PDTCs)
Introduced on July 1, 2019, the PDTC check is an integral part of the BAR-OIS Smog Check inspection. PDTCs function similarly to regular DTCs but differ in their persistence. Unlike regular DTCs, which can be cleared by using a scan tool or disconnecting the battery, PDTCs can only be cleared by the OBD system itself after confirming the resolution of the previously detected fault.
While a stored PDTC will trigger a failed PDTC check irrespective of the MIL status, certain conditions allow for ignoring the PDTC presence. If the vehicle has undergone at least 15 warm-up cycles and accumulated 200 miles since the last OBD information clearing, the PDTC presence is disregarded. However, some vehicles face challenges in clearing specific PDTCs, and ongoing efforts are being made to address these issues with manufacturers.
Modified Software Standards
Implemented on July 19, 2021, the modified software check aims to detect illegal modifications to a vehicle’s software that could impact emissions. Software modifications approved by the California Air Resources Board (CARB) are exempt from this check. Vehicles found to have illegally modified software will fail the Smog Check inspection. Restoration to OEM-approved or CARB-approved software is required before retesting.
Conclusion
Disabling OBD2 codes is not a solution for passing emissions tests. Understanding the intricacies of the OBD system, including readiness monitors, MIL status, communication protocols, PDTCs, and modified software regulations, is crucial for properly diagnosing and addressing emission-related problems. Addressing the underlying issue that triggered the code is the correct way to ensure your vehicle is running efficiently and meets emissions standards. If you encounter persistent issues with OBD2 codes, consulting a qualified automotive technician or referring to vehicle-specific resources is recommended.
