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Home >> Isuzu >> 2007 >> i-290 LS, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 14 (Fixed & MOVEABLE Window Systems) >> Diagnostic Information and Procedures >> Rear Window Defogger Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2007 Cadillac DTS. 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 OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal 11 and ground.
    • If greater than the specified range, test for an open/high resistance.
  3. Ignition ON, verify that a test lamp does not illuminate between the output circuit terminal 12 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 14 and ground.
    • If the test lamp does not illuminate, test the 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 output circuit terminal 12 for a short to ground.
  5. Ignition OFF, disconnect the harness connector at the defogger grid.
  6. Ignition OFF, test for less than 1.0 ohm of resistance between the defogger grid ground circuit terminal A and B and ground.
    • If greater than the specified range, test the ground circuits for an open/high resistance.
  7. Connect the harness connector at the defogger grid.
  8. Ignition ON, connect a 40A fused jumper wire between the B+ circuit terminal 14 and the output circuit terminal 12. Verify the defogger grid is activated.
    • If the defogger grid does not activate, test the control circuit for 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 15 and the ground circuit terminal 11.
  10. Command the rear defogger grid ON and OFF by pressing 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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