Rear Window Defogger Description and Operation

REAR DEFOGGER SYSTEM COMPONENTS
The rear window defogger system consist of the following components:
^ An HVAC control module
^ An Instrument Panel Integration Module (IPM)
^ A Rear Integration Module (RIM)
^ A RR DEFOG relay
^ A rear window that has a number of grid lines
^ Two bus bars that are attached to the inside surface of the rear window.

The battery voltage terminal and ground terminal are soldier to the bus bars.

REAR WINDOW DEFOGGER OPERATION
Battery positive voltage is supplied through the RR DEFOG fuse to the RR DEFOG relay switch. Ignition 1 voltage is supplied to the RR DEFOG relay coil. When you turn the ignition to the ON position, and depress the rear window defogger switch. The HVAC control module sends a message via the data signal circuit of the HVAC control module to the IPM to enable the rear window defogger system. The IPM sends this message via class 2 message to the RIM. The RIM energizes the RR DEFOG relay by grounding the control circuit of the relay. This allows battery positive voltage to the rear window defogger. The RIM then sends a class 2 message to the IPM requesting the illumination of the rear window defogger indicator. The IPM sends this 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 G310.

When you turn ON the ignition and press the rear window 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 window 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.