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Home >> Cadillac >> 2007 >> Escalade EXT >> Repair and Diagnosis >> External Pages >> Different car >> Section 1609 (Fixed And MOVEABLE Windows System) >> Diagnostic Information and Procedures >> Rear Window Defogger Malfunction >> Circuit/System Testing
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Circuit/System Testing

WARNING: This page is about a different car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the REAR DEFOG relay.
  2. Test for less than 1 ohm between the ground circuit terminal 85 and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
    • If the test lamp illuminates, test the control circuit for a short to voltage.
  4. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  5. Ignition OFF, disconnect the X2 harness connector at the defogger grid.
  6. Test for less than 5 ohms between the defogger grid ground circuit terminal A and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the harness connector at the defogger grid.
  8. Ignition ON, connect a 30A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the defogger grid is activated.
    • If the defogger grid does not activate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the defogger grid.
  9. Connect a test lamp between the control circuit terminal 86 and ground.
  10. Command the defogger grid ON and OFF by pressing and depressing the rear defogger switch. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.
    • If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
  11. If all circuits test normal, test or replace the REAR DEFOG relay.
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