2002 GMC Envoy Owner's Manual - Page 158

Service Four-Wheel-Drive Warning Light (If Equipped) Check Gages Light United States United States Canada Canada This light should come on briefly when you turn on the ignition, as a check to show you it is working. The SERVICE 4WD light comes on to indicate that there may be a problem with the drive system and service is required. Malfunctions can be indicated by the system before any problem is apparent, which may prevent serious damage to the vehicle. This system is also designed to assist your service technician in correctly diagnosing a malfunction. The CHECK GAGES light will come on briefly when you are starting the engine. If the light comes on and stays on while you are driving, check your coolant temperature and engine oil pressure gages to see if they are in the warning zones. 2-89