Readiness monitors and the Malfunction Indicator Lamp (MIL) are crucial components of your vehicle’s On-Board Diagnostic (OBD) system. This article summarizes pass/fail standards for the OBD test portion of a Smog Check inspection, specifically focusing on OBDII requirements for vehicles designated as “3inc” (allowing three incomplete monitors) and “5 ready” (requiring five ready monitors). We’ll also address common issues encountered during OBD testing.
OBDII Readiness Monitors and Smog Checks
Your vehicle’s OBD system continuously performs self-tests called readiness monitors to ensure the emission control system is functioning correctly. These monitors track various components, and their status (complete or incomplete) is crucial for passing a Smog Check.
The number of incomplete monitors permissible varies by vehicle year and fuel type. Generally, older gasoline vehicles (1996-1999) fall under the “3inc” category, allowing up to three incomplete monitors. However, most modern gasoline vehicles require all monitors to be complete except for the evaporative system monitor. Diesel vehicles have different standards, often focusing on Particulate Filter and NMHC monitor readiness.
Common reasons for incomplete monitors include infrequent driving, specific driving conditions not being met, and malfunctioning emissions components.
A standard OBDII connector.
Malfunction Indicator Lamp (MIL) Status
The MIL, often referred to as the “Check Engine” light, plays a significant role in the OBD test. For a vehicle to pass, the MIL must illuminate when the ignition is on and the engine is off (KOEO) and turn off when the engine is running (KOER). A constantly illuminated MIL indicates a potential problem and will result in a failed test. Conversely, a MIL that doesn’t illuminate during the KOEO test also signifies a failure.
OBDII Communication Protocols
Successful communication between the OBD system and the testing equipment is essential. Failures can stem from various issues, including a damaged OBDII connector, faulty wiring, aftermarket installations interfering with communication, and the transmission control module responding instead of the engine control module. The BAR-97 test requires communication with the BAR-97 system, while the OIS (On-board Diagnostic Inspection System) mandates communication and the transmission of specific data points.
Permanent Diagnostic Trouble Codes (PDTCs)
Vehicles from 2010 onwards utilize PDTCs. These codes, unlike regular DTCs, persist even after clearing DTCs with a scan tool or disconnecting the battery. A stored PDTC generally results in a failed Smog Check. However, there are exceptions for specific vehicles known to have issues clearing certain PDTCs. Additionally, a PDTC check is bypassed if the vehicle has undergone sufficient driving (at least 15 warm-up cycles and 200 miles) since the last OBD information clear.
A scan tool reading data from an OBDII connector.
Modified Software and OBDII Compliance
Software modifications to the vehicle’s engine control unit (ECU) can impact emissions and OBDII compliance. Software approved by the California Air Resources Board (CARB) is acceptable. However, unauthorized modifications will lead to a failed inspection. Vehicles with modified software must be restored to their original or CARB-approved configuration before retesting.
Vehicle Specific OBDII Issues
Certain vehicle makes and models exhibit known OBDII-related problems, impacting readiness monitors, communication, and MIL status. These issues can be attributed to design anomalies, software glitches, or specific component malfunctions. Many manufacturers have issued Technical Service Bulletins (TSBs) or recalls to address these problems. Consulting these resources is vital for accurate diagnosis and repair. The provided table lists specific vehicles and their corresponding OBDII issues, causes, and potential solutions. It serves as a valuable reference for technicians diagnosing and addressing OBDII-related Smog Check failures.
Conclusion
Understanding the intricacies of OBDII systems, readiness monitors, MIL status, communication protocols, and PDTCs is paramount for passing a Smog Check inspection. Addressing known vehicle-specific issues and ensuring compliance with modified software regulations are also crucial. By adhering to these guidelines and consulting manufacturer resources, vehicle owners can ensure their vehicles meet the necessary OBDII requirements for Smog Check compliance.
