1997 Chevrolet Express Van Owner's Manual - Page 115

If the light stays on, or comes on when you're driving, your vehicle needs service. If the regular brake system warning light isn't on, you still have brakes, but you don't have anti-lock brakes. If the regular brake system warning light is also on,you don't have anti-lock brakes and there's a problem with your regular brakes. See "Brake System Warning Light" earlier in this section. The anti-lock brake system warning light should come on briefly when you turn the ignition key to RUN. If the light doesn't come on then, have it fixed so it will be ready to warn you if there is a problem. Malfunction Indicator Lamp (Service Engine Soon Light) (Gasoline Engine) Your vehicle is equipped with a computer which monitors operation of the fuel, ignition and emission control systems. SERVICE ENGINE SOON Daytime Running Lamps Indicator Light You may have this light on the instrument panel. It will light whenever the DRL are on. It is also a reminder to turn on your headlamps when driving at night. For more details about DRL, see "Headlamps and Vehicle Lighting" in this section. This system is called OBD I1 (On-Board Diagnostics-Second Generation) and is intended to assure that emissions are at acceptable levels for the life of the vehicle, helping to produce a cleaner environment. (In Canada, OBD IT is replaced by Enhanced Diagnostics.) The SERVICE ENGINE SOON light comes on to indicate that there is a problem and service is required. Malfunctions often will be indicated by the system before any problem is apparent. This may prevent more serious damage to your vehicle. This system is also designed to assist your service technician in correctly diagnosing any malfunction.