Rear Window Defrost

The rear window defrost system only operates when the engine is running. When the rear window defrost switch is activated, the HVAC module sends the request message to the BCM and then through a LIN to the BJB. The BJB activates the rear window defrost relay (integral to the BJB). When the rear window defrost relay is activated, the rear window defrost grid(s) are energized. In some cases, the rear window defrost system may automatically activate as an extra load for accelerated engine warm-up. However the rear window defrost status LED remains off unless the rear window defrost switch is activated.

The BJB deactivates the rear window defrost relay when any of these conditions is met:

• The rear window defrost switch is pressed when the feature is active.
• Ignition state is changed from on to off.
• A predetermined timer completes.
• Battery voltage has dropped below a specified threshold (load management strategy).