Performing an OBD2 driving cycle is crucial for General Motors (GM) vehicles after certain repairs or when preparing for an emissions test. This process allows your vehicle’s onboard computer to run self-tests on various emission control systems. Completing a GM OBD2 driving cycle ensures all systems are checked and that your vehicle is running efficiently. Using an OBD2 code reader can help monitor the status of these tests, ensuring they are completed successfully. This guide provides a step-by-step approach to execute a GM OBD2 driving cycle effectively.
1. Cold Start
Begin with a cold start. For a valid cold start, the engine coolant temperature needs to be below 122°F (50°C) and within 11°F (6°C) of the ambient air temperature at startup. Ensure the key is not in the ignition prior to starting, as this could prevent the heated oxygen sensor diagnostic from running correctly.
2. Idle
Let the engine idle for two and a half minutes with the air conditioner and rear defroster turned on. Increasing the electrical load during this stage is beneficial. This idle period tests components such as the O2 heater, Passive Air system, Purge “No Flow,” and Misfire detection. If closed-loop operation is achieved, it also tests Fuel Trim.
3. Accelerate
Turn off the air conditioner and all other electrical loads. Then, accelerate smoothly using half throttle until you reach 55mph (88km/hr). During this acceleration, the system will evaluate Misfire, Fuel Trim, and Purge Flow diagnostics.
4. Hold Steady Speed
Maintain a constant speed of 55mph (88km/hr) for three minutes. This steady speed phase is critical for testing O2 response, air Intrusive system, EGR, Purge, Misfire, and Fuel Trim diagnostics.
5. Decelerate
Release the accelerator pedal completely and allow the vehicle to coast down to 20 mph (32km/hr). It is important not to shift gears, or touch the brake or clutch pedals during deceleration. This coasting period enables testing of the EGR, Purge, and Fuel Trim diagnostics.
6. Accelerate Again
Accelerate again, this time using 3/4 throttle, until reaching a speed between 55-60mph (88-96 km/hr). This step repeats the diagnostics performed in step 3, again checking Misfire, Fuel Trim, and Purge Flow.
7. Hold Steady Speed (Extended)
Maintain a steady speed of 55mph (88km/hr) for a longer duration of five minutes. In addition to the diagnostics from step 4, this extended steady speed period allows the catalyst monitor diagnostics to run. If the catalyst is marginal or the battery has recently been disconnected, it might require up to 5 complete driving cycles to accurately assess the catalyst’s condition.
8. Final Deceleration
Perform a final deceleration similar to step 5. Release the accelerator and coast down to 20 mph (32km/hr) without using the brake or clutch pedals, or shifting gears. This step again tests the EGR, Purge, and Fuel Trim diagnostics.
By following these steps, you can effectively perform a GM OBD2 driving cycle. After completing the cycle, use your OBD2 code reader to check if all readiness monitors have been set. This will confirm whether your vehicle is ready for an emissions test or if further diagnostics are needed.
