2004 GMC Sonoma Owner's Manual - Page 137

Security Light This light will come on briefly when you turn the key toward START. The light will stay on until the engine starts. Service Four-Wheel Drive Warning Light If you have this light, it should come on briefly when you turn on the ignition, as a check to show you it is working. If the light flashes, the Passlock® system has entered a tamper mode. If the vehicle fails to start, see Passlock® on page 2-16. If the light comes on continuously while driving and stays on, there may be a problem with the Passlock® system. Your vehicle will not be protected by Passlock®, and you should see your dealer. Also, see Content Theft-Deterrent on page 2-14 for additional information regarding the SECURITY light. The SERVICE 4WD light comes on to indicate that there may be a problem with the four-wheel 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. 3-33