The rear window defogger system consist of the following components:

Battery positive voltage is supplied through the REAR DEFOG fuse to the HTD BK LITE relay switched input. Ignition voltage is supplied through the IGN SEN fuse to the HTD BK LITE relay coil. When you turn the ignition to the ON position, and the rear defogger switch is depressed. The HVAC control module sends a message via the data signal circuit to the IPM requesting the activation the rear window defogger. The IPM sends a class 2 message to the BCM to enable the rear window defogger system. The BCM energizes the HTD BK LITE 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 radio antenna module and then to the rear window defogger. The BCM then sends a class 2 message to the IPM requesting illumination of the rear window defogger indicator. In response to this request the IPM sends a message via the data signal circuit to the HVAC control module. The HVAC control module illuminates the rear window defogger indicator. Ground for the rear window defogger is provided by the radio antenna module coil.

When you turn ON the ignition and press the rear defogger switch for the first time, the defogger cycle lasts 10 minutes. Further operation results 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 rear defogger feature is disabled.