2008 GMC Envoy Owner's Manual - Page 177

If the Light is Flashing The following can prevent more serious damage to your vehicle: improperly installed. A loose or missing fuel cap allows fuel to evaporate into the atmosphere. A few driving trips with the cap properly installed should turn the light off. Did you just drive through a deep puddle of water? If so, your vehicle's electrical system might be wet. The condition is usually corrected when the electrical system dries out. A few driving trips should turn the light off. Have you recently changed brands of fuel? If so, be sure to fuel your vehicle with quality fuel. See Gasoline Octane on page 5-6. Poor fuel quality causes the engine not to run as efficiently as designed. You might notice this as stalling after start-up, stalling when you put the vehicle into gear, misfiring, hesitation on acceleration, or stumbling on acceleration - these conditions might go away once the engine is warmed up. This will be detected by the system and cause the light to turn on. If you experience one or more of these conditions, change the fuel brand you use. It will require at least one full tank of the proper fuel to turn the light off. If none of the above steps have made the light turn off, your dealer/retailer can check the vehicle. Your dealer/retailer has the proper test equipment and diagnostic tools to fix any mechanical or electrical problems that might have developed. Reduce vehicle speed. Avoid hard accelerations. Avoid steep uphill grades. If you are towing a trailer, reduce the amount of cargo being hauled as soon as it is possible. If the light stops flashing and remains on steady, see "If the Light Is On Steady" following. 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 ignition off, wait at least 10 seconds, and restart the engine. If the light remains on steady, see "If the Light Is On Steady" following. If the light is still flashing, follow the previous steps and see your dealer/retailer for service as soon as possible. If the Light Is On Steady You might be able to correct the emission system malfunction by considering the following: Did you recently put fuel into your vehicle? If so, reinstall the fuel cap, making sure to fully install the cap. See Filling the Tank on page 5-8. The diagnostic system can determine if the fuel cap has been left off or 3-43