2004 Chevrolet Astro Owner's Manual - Page 155

Security Light This light will come on briefly when you turn the ignition key to START. Service All-Wheel Drive Light This light should come on briefly when you turn on the ignition, as a check to show you it is working. The light will stay on until the engine starts. 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 GM dealer. The SERVICE AWD 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. 3-35