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Home >> GMC >> 2006 >> Sierra 1500 HD, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 992 (Fixed & MOVEABLE Window Systems) >> Diagnostic Information and Procedures >> Rear Window Defogger Malfunction >> Circuit/System Description

Circuit/System Description

WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

When the rear defogger button is pressed, voltage is supplied to the relay coil by the HVAC control module which also illuminates the rear window defogger indicator. B+ voltage is supplied at all times to the relay switched input and the relay coil is always grounded. This allows battery positive voltage from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger. Ground for the rear defogger grid is provided by G304 or G307.

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