Rear Window Defogger System Components
The rear window defogger system consist of the following components:
• | HVAC control module, contains switch and indicator |
• | Body control module (BCM) |
• | Rear window defogger grid |
• | RR DEFOG relay--located in the instrument panel (I/P) fuse block |
• | RR DEFOG fuse--located in the underhood fuse block |
Rear Window Defogger Operation
With the ignition in the RUN position, and the rear window defogger switch depressed
a class 2 serial data message is sent from the HVAC control module to the body
control module (BCM) requesting rear defog operation. The BCM responds by providing
ground to the rear defog control signal circuit energizing the RR defog relay. The
RR defog relay then provides voltage to the rear defog element supply voltage circuit
operating the rear defog system. The HVAC control module illuminates the rear window
defogger indicator when a class 2 serial data message is received indicating
that the BCM is requesting rear defog operation. The RR defog relay receives battery
positive voltage to both the coil and switch input sides from the RR DEFOG fuse in
the underhood fuse block. Ground for the rear window defogger is provided at G401
or G400.
When you start the engine and press the rear window defogger switch for the
first time, the defogger cycle lasts for 15 minutes. Further operation results
in 7.5 minute defogger cycles. The defogger cycle resets to 15 minutes
when you cycle the ignition to the OFF position and then back to the ON position.
If battery voltage is low, the BCM will disable the rear window defogger.