The service engine light on your GMC will come on when you need regular maintenance. The service light is designed to come on after a preset number of miles for various maintenance procedures (when the light comes on depends on the maintenance procedure). Once you've performed the necessary maintenance, you need to know how to reset the service light. Failure to reset the light will mean that you won't be warned when future maintenance needs to be done. If maintenance is ignored, this can cause premature failure of various fuel and engine components like the fuel filter, pump, and catalytic converter.
Open the fuse panel by pulling down on the panel under the steering column with your fingers.
Pull the fuse for the electronic control unit, ECU, using the fuse pullers in the fuse panel. Use the fuse diagram on the underside of the fuse panel to locate the fuse for the ECU.
Turn the ignition on but don't crank the engine.
Wait five minutes before replacing the ECU fuse. The "service engine soon" light on the dash will blink and then shut off. This will reset the light.