2009 GMC Yukon Owner's Manual - Page 229

Notice: Modifications made to the engine, transmission, exhaust, intake, or fuel system of the vehicle or the replacement of the original tires with other than those of the same Tire Performance Criteria (TPC) can affect the vehicle's emission controls and can cause this light to come on. Modifications to these systems could lead to costly repairs not covered by the vehicle warranty. This could also result in a failure to pass a required Emission Inspection/Maintenance test. See Accessories and Modifications on page 5-3. This light comes on during a malfunction in one of two ways: Light Flashing: A misfire condition has been detected. A misfire increases vehicle emissions and could damage the emission control system on the vehicle. Diagnosis and service might be required. To prevent more serious damage to the vehicle: Reduce vehicle speed. Avoid hard accelerations. Avoid steep uphill grades. If towing a trailer, reduce the amount of cargo being hauled as soon as it is possible. If the light continues to flash, when it is safe to do so, stop the vehicle. Find a safe place to park the vehicle. Turn the key off, wait at least 10 seconds, and restart the engine. If the light is still flashing, follow the previous steps and see your dealer/retailer for service as soon as possible. Light On Steady: An emission control system malfunction has been detected on the vehicle. Diagnosis and service might be required. 3-45