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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1811 (Fixed And MOVEABLE Windows) >> Diagnostic Information and Procedures >> Rear Window Defogger Inoperative >> Circuit/System Testing >> Rear Defogger Malfunction

Rear Defogger Malfunction

WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the REAR DEFOG relay.
  2. Ignition ON, verify a test lamp does not illuminate between the relay controlled output circuit terminal and ground.
    • If the test lamp illuminates, test the relay controlled output circuit for a short to voltage.
  3. Verify a test lamp illuminates between the relay coil B+ circuit terminal and ground.
    • If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test or replace the relay REAR DEFOG relay.
  4. Verify a test lamp illuminates between the relay switch B+ circuit terminal and ground.
    • If the test lamp does not illuminate, test the relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the REAR DEFOG fuse is open, test the relay controlled output circuit for a short to ground.
  5. Disconnect the harness connector C2 at the rear window defogger grid.
  6. Ignition OFF, test for less than 1.0 ohm of resistance between the 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 C2 at the rear window defogger grid.
  8. Ignition ON, connect a 25 A fused jumper wire between the relay switch B+ circuit terminal and the relay controlled output circuit terminal. Verify the rear window defogger grid is activated.
    • If the rear window defogger grid does not activate, test the relay controlled output circuit for an open/high resistance. If the circuit tests normal, test or replace the rear window defogger grid.
  9. Connect a test lamp between the relay coil B+ circuit terminal and the relay coil control circuit terminal.
  10. Command the rear window defogger ON and OFF with a scan tool. 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 BCM.
    • If the test lamp is always OFF, test the relay coil control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  11. If all circuits test normal, test or replace the REAR DEFOG relay.
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