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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 873 (Fixed & MOVEABLE Window Systems) >> Diagnostic Information and Procedures >> Rear Window Defogger Inoperative >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition ON, verify that the rear defogger indicator illuminates when the switch is activated.
    • If the indicator does not illuminate when system operation is attempted, replace the HVAC control module.
  2. Connect a test lamp from the supply side of the REAR DEFOG fuse to ground.
  3. Verify that the test lamp is illuminated while the rear defogger is turned on.
    • If the test lamp does not illuminate test the battery supply circuit to the REAR DEFOG relay for an open/high resistance or short to ground. If the circuit tests normal replace the REAR DEFOG relay.
  4. Disconnect the rear defogger grid connectors and verify that a test lamp illuminates when connected from battery voltage to the ground circuit connector.
    • If the test lamp does not illuminate repair the ground circuit for an open/high resistance.
  5. Connect a test lamp across the rear defogger grid connectors and verify that the test lamp illuminates when the defogger is turned on.
    • If the test lamp does not illuminate repair the defogger grid supply circuit for an open/high resistance.
  6. If the circuits test normal replace the rear window defogger grid.
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