The rear window defogger system consists of the following components:

The HVAC control module controls the REAR DEFOG relay located in the underhood fuse block. The rear window defogger switch is located on the radio/HVAC control panel at the center of the dash. When the rear window defogger switch is activated ON, the radio/HVAC control panel sends a serial data message to the HVAC control module requesting the rear defogger be activated. The HVAC control module responds by energizing the rear defog relay by applying voltage to the relay coil via the rear defog relay control circuit. Ground for the relay coil is provided at ground G104. When the rear defog relay coil is energized, the switch contacts of the rear defog relay close allowing battery voltage to flow from the REAR DEFOG fuse through the closed switch contacts and out the relay switched output circuit to the rear window defogger grid. Ground for the rear window defogger grid is provided at grounds G401 and G402. The information display module also illuminates the rear defog indicator LED located on the information display module panel.

When you start the engine and activate the rear window defogger switch, the defogger cycle lasts for 15 minutes. Further operation will result in 7.5 minute defogger cycles. The rear window defogger cycle resets to 15 minutes when the ignition is cycled from OFF to ON.

The rear window defogger will not time out if vehicle speed is above 50 mph (80 km/h).