1997 GMC Sonoma Owner's Manual - Page 109

If the Light Is Flashing The following may prevent more serious damage to your vehicle: 0 Reducing vehicle speed. Avoiding hard accelerations. Avoiding 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 flashingand 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 your vehicle. Turn the key off, wait at least 10 secondsand 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 drive the vehicle to your dealer orqualified service center for service. If the LightIs On Steady You may 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. The diagnosticsystem can determine if the fuel cap has been left off or improperly installed.A loose or missing fuel cap will allow 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 deeppuddle of water? If so, your electrical system may be wet. The condition will usually be 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 "Fuel" in the Index). Poor fuel quality will cause your engine not to run as efficiently as designed. You may 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 may go away once the engineis warmed up.) This will be detected by the system and cause thelight 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 fuelto turn the light off. If none of the above steps have made the light turn off, have your dealer orqualified service center check the vehicle. Your dealer has the proper test equipment and diagnostic tools to fix any mechanical or electrical problems that may have developed. 2-61