The rear window defogger system consist of the following components:

Battery positive voltage is supplied through the REAR DEFOG fuse located in the right rear fuse block to the REAR DEFOG relay switched input. When the rear window defogger switch is depressed, the HVAC control module sends a message via GMLAN serial data to the rear integration module (RIM) to enable the rear window defogger system. The RIM energizes the REAR DEFOG relay by grounding the control circuit of the relay. This allows battery positive voltage from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger. The RIM then sends a message via GMLAN serial data to the HVAC control module requesting the illumination of the rear window defogger indicator. Ground for the rear window defogger grid is provided by G403 and G404.

When you start the engine and depress the rear window defogger switch, the defogger cycle lasts for 10 minutes. Further operation will result in 5 minute defogger cycles. The defogger cycle resets to 10 minutes when you cycle the ignition to the OFF position and then back to the ON position.

The rear defogger feature will not time out if the vehicle speed is above 48 km/h (30 mph).

If the battery voltage is very low, the RIM will execute a load shed management control algorithm for the rear defogger feature. In Load Shed Level 1, the rear defogger is cycled at 80 percent ON and 20 percent OFF. In Load Shed Level 2, the rear defogger is cycled at 50 percent ON and 50 percent OFF. In Load Shed Level 3, the rear defogger is cycled at 100 percent OFF. For more information about Load Shed, refer to Load Shed System Description and Operation.