Rear Window Defogger Description and Operation
Rear Window Defogger System Components
The rear window defogger system consist of the following components:
• The HVAC control module
• The body control module (BCM)
• The rear defogger relay
• The rear window grid
Rear Window Defogger Operation
The BCM supplies 12
V to the rear window defogger switch signal circuit to the HVAC control module. When you depress the rear
window defogger switch, the rear window defogger switch pulls the signal circuit low. The BCM interprets as a request for the rear
window defogger system. The BCM enables the rear window defogger system by supplying voltage to the rear defogger relay coil.
The relay coil supply voltage is also spliced off internally in the BCM to the supply voltage circuit of the rear window defogger
indicator. The rear defogger relay is energized and the rear window defogger indicator is illuminated. With the relay energized,
battery positive voltage is allowed from the relay switched input through the switch contacts and out the relay switched output to
the rear window defogger grid.
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 rear defogger feature will not time out if vehicle speed is above 80
km/h
(50
mph). The defogger cycle resets to 15
minutes when you cycle the ignition to the OFF position and then to the ON position.
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Fixed and Movable Windows
BODY SYSTEMS
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CHEVROLET SONIC 2012 BODY REPAIR MANUAL
