Ensuring your vehicle passes OBD2 emissions testing is crucial, and a key part of this is the readiness of your EGR (Exhaust Gas Recirculation) monitor. Often, after repairs or battery disconnection, this monitor, along with others, may show as incomplete (“inc”) on your OBD2 scanner. A specific driving pattern, known as a drive cycle, can help reset these monitors. While various drive cycles exist, the General Motors (GM) drive cycle is quite comprehensive and often effective for multiple vehicle makes, including Jeep. This guide explains the GM OBD2 drive cycle to help you complete your EGR monitor and other system checks.
To initiate the GM OBD2 driving cycle, adhere to these steps precisely:
1. Cold Start: Begin with a cold engine. The engine coolant temperature should be below 122°F (50°C) and within 11°F (6°C) of the ambient air temperature. Avoid turning the ignition key to the “on” position before starting, as this can prevent the heated oxygen sensor diagnostic from running correctly.
2. Idle Phase: Start the engine and let it idle for two and a half minutes. Maximize electrical load by turning on the air conditioner and rear defroster. This idle period is critical for testing components like the O2 sensor heater, Passive Air system, Purge “No Flow” detection, and Misfire diagnostics. It also allows the system to achieve closed loop operation and assess Fuel Trim.
3. Acceleration: Turn off the air conditioner and all other electrical loads. Accelerate smoothly at half throttle until you reach 55 mph (88 km/hr). This acceleration phase engages the Misfire, Fuel Trim, and Purge Flow diagnostics.
4. Steady Speed Hold (1): Maintain a constant speed of 55 mph (88 km/hr) for three minutes. This steady speed segment facilitates the operation of O2 response, air intrusion checks, EGR system diagnostics, Purge system checks, Misfire detection, and Fuel Trim adjustments.
5. Deceleration: Release the accelerator pedal completely and allow the vehicle to coast down to 20 mph (32 km/hr). Do not use the brakes, clutch, or shift gears during deceleration. This phase is important for evaluating EGR, Purge, and Fuel Trim systems under changing engine load conditions.
6. Acceleration (2): Accelerate again, this time at 3/4 throttle, until you reach a speed between 55-60 mph (88-96 km/hr). This step repeats the diagnostics performed in step 3, ensuring thorough evaluation under slightly different acceleration parameters.
7. Steady Speed Hold (2): Hold a steady speed of 55 mph (88 km/hr) for a longer duration of five minutes. In addition to the diagnostics from step 4, this extended steady speed period is essential for the catalyst monitor diagnostics. If your catalytic converter is marginal or the battery has been recently disconnected, it might require up to five complete driving cycles to accurately assess its condition.
8. Final Deceleration: Similar to step 5, release the accelerator and allow the vehicle to coast down without using brakes or shifting gears. This final deceleration mirrors step 5’s diagnostic focus, providing a concluding check of EGR, Purge, and Fuel Trim systems.
By diligently following these steps, you provide your vehicle’s onboard diagnostic system with the conditions needed to run comprehensive tests, including those for the EGR monitor. Completing this GM driving cycle can effectively reset your OBD2 readiness monitors, potentially resolving an “Egr Inc Obd2” status and ensuring your vehicle is ready for emissions testing.
Reprinted on OBDII web site courtesy of General Motors Corporation © General Motors Corporation
