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Home >> Hummer >> 2008 >> H3 Base, Automatic >> Repair and Diagnosis >> Body & Frame >> Fixed And MOVEABLE Windows >> Diagnostic Information and Procedures >> Rear Window Defogger Malfunction >> Circuit/System Testing

Circuit/System Testing

Rear Window Defogger Switch Malfunction

  1. Ignition OFF, disconnect the X2 harness connector at the HVAC control module.
  2. Test for less than 1 ohm between the ground circuit terminal L and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Rear Defog Switch parameter is Inactive.
    • If not the specified value, test the rear defog signal circuit terminal J for a short to ground. If the circuit tests normal, replace the BCM.
  4. Install a 3A fused jumper wire between the signal circuit terminal J and ground. Verify the scan tool Rear Defog Switch parameter is Active.
    • If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the HVAC control module.

Rear Window Defogger Malfunction

  1. Ignition OFF, disconnect the RR 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 1 ohm 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 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 Rear Defog Relay 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 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 RR DEFOG relay.

Rear Window Defogger Indicator Malfunction

  1. Ignition OFF, disconnect the X2 harness connector at the HVAC control module.
  2. Disconnect the RR DEFOG relay.
  3. Connect a test lamp between the control circuit terminal 86 and ground.
  4. Ignition ON, 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 control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the HVAC control module.
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