1995 GMC Sonoma Owner's Manual - Page 107

Malfunction Indicator Lamp (SERVICE ENGINE SOON Light) Your vehicle is equipped with an onboard computer which monitors is operation of the emission control system. This system called OBD I1 (On-Board Diagnostics-Second Generation) andis intended to assurethat emissions are atacceptable levels for the life of the vehicle, helping to produce a cleaner environment. The"SERVICE ENGINE SOON" light comes on to indicate when service required. Malfunctions often will be is indicated by the system before any problem is apparent, which may prevent more serious damageto your vehicle. This system is also designed toassist your service technician in correctly diagnosing any malfunction. The "SERVICE ENGINE SOON"light should come on, as check to show a you it is working, when the ignition is on and the engine isnot running. This light will also come duringa malfunction in one of two ways: Light on steady - indicates a system malfunction has been detected. at Drive the vehicle to the dealer for service your firstopportunity. Light flashing - indicates a misfire has been detected which may damage the emission control system. The damage be reduced by may lowering the vehicle speed, reducing the amountcargo beinghauled of or trailered, avoidinghard acceleration, or by avoiding steepuphill grades. If these actions are effective, the light will stop flashingand remain on steady. Drive the vehicle to a dealer for service.If the light continues to flash, stop the vehicle. Wait for a steady light to come on, a then drive the vehicle to dealer for service. These following conditions also may cause "SERVICE ENGINE the SOON' light to come on: Low FueVOut of Fuel - As the vehicle starts to run out of fuel the "SERVICE ENGINE SOON' light may come on as a result of an engine misfire. Filling your gasoline tank should correct this condition. Make sure to install the gas capfully. It will require a few driving trips to turn the light off * Poor Quality Fuel - Be sureto fuel your vehicle with quality fuel. Your engine may not run efficiently on poor fuel. Poorfuel may cause stalling, hesitation or misfire. These conditionsmay go away when the engine is warned-up. However, poor quality fuelmay cause the "SERVICE ENGINE SOON" light to come on. you Have a dealer check the vehicle. If no problems are found, may want to change to another brand of fuel. through puddles Driving Through Standing Water - Driving your vehicle of deep standing water may result in a temporary misfire condition. This condition will usually correct itself shortly after the electrical system dries out. It will require a few driving trips to turn the light off. 2-61