2009 Chevrolet Silverado 2500 HD Extended Cab Owner's Manual - Page 232

If the check engine light comes on and stays on, while the engine is running, this indicates that there is an OBD II problem and service is required. Malfunctions often are indicated by the system before any problem is apparent. Being aware of the light can prevent more serious damage to the vehicle. This system assists the service technician in correctly diagnosing any malfunction. Notice: If the vehicle is continually driven with this light on, after a while, the emission controls might not work as well, the vehicle's fuel economy might not be as good, and the engine might not run as smoothly. This could lead to costly repairs that might not be covered by the vehicle warranty. 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 5-4. 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. 3-46