It all depends on the type of driving you've done over a one week period. Was it just city driving? Did you take your Yukon on the highway? You need both city and highway driving to complete or reset the emission monitors. In most cases, the emission monitors should run during normal vehicle operation. Due to different driving habits however, the criteria required to run a monitor may not always be met and following the GMC Yukon cycle below may be required. Take extra caution when performing the drive cycle on public roadways. Perform the drive cycle at your own risk.
You may choose to have a GMC dealer or smog check repair station complete the monitor readiness while your SUV is stationary via the use of a scan tool and a dynamomoter. An advanced scan tool will have the capability to command your Yukon's engine control module (ECM) to run readiness code diagnostic tests in a special operational mode.
A little background on why you have to drive you GMC Yukon in order to reset the monitors... Emission Monitors are self tests which the engine's ECM (engine control module) conducts to ensure the emission system is functioning properly. The self tests are performed during various stages of driving and while the vehicle is under load, idle and shut off, hence the neccessity of driving a vehicle in order to reset or make complete the required emission monitors.
How To Perform a GMC Yukon Drive Cycle to Reset Emission Monitors
- Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 50°C (122°F) and within 6°C (11°F) of the ambient air temperature at startup. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.
- Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.
- Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.
- Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.
- Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.
- Accelerate. Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same diagnostics as in step 3.
- Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.
- Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.
This completes the GMC Yukon Drive Cycle. Use a scan tool to check the status of the emissions monitors (readiness flags) now. If any are incomplete, perform the drive cycle again. Remember the drive cycle should always be started when the engine is cold, and also ensure the check engine or service engine soon light is not on. The drive cycle will not initiate if the service engine soon or check engine lights are on.
