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Home >> Hummer >> 2008 >> H3 Base, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 3 (Lighting Systems) >> Diagnostic Information and Procedures >> Front Fog Lamps Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2008 Isuzu i-370, 2008 Isuzu i-290, 2008 GMC Canyon, and 2008 Chevrolet Colorado. However, it is still accessible from the selected car via links, so may be relevant.

Fog Lamp Relay Circuit Test

  1. Ignition OFF, disconnect the front fog lamp relay.
  2. Test for less than 5 ohms between the relay coil ground circuit terminal 86 and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify a test lamp does not illuminate between the fog lamp control circuit terminal 30 and ground.
    • If the test lamp illuminates, test the fog lamp control circuit for a short to voltage.
  4. Verify a test lamp illuminates between the relay switch B+ circuit terminal 87 and ground.
    • If the test lamp does not illuminate, replace the underhood fuse block.
  5. Disconnect the harness connector at an affected fog lamp.
  6. Ignition OFF, test for less than 5 ohms between the ground circuit terminal B and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the harness connector at the fog lamp.
  8. Ignition ON, connect a 15A fused jumper wire between the relay switch B+ circuit terminal 87 and the fog lamp control circuit terminal 30. Verify the front fog lamps are on.
    • If the front fog lamps do not turn on, test the fog lamp control circuit for an open/high resistance. If the circuit tests normal, test or replace the affected fog lamp bulb.
    • If the fuse in the jumper wire opens, test the fog lamp control circuit for a short to ground.
  9. Connect a test lamp between the relay coil control circuit terminal 85 and ground.
  10. Command the front fog lamps 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 open/high resistance. If the circuit tests normal, replace the BCM.
  11. If all circuits test normal, test or replace the front fog lamp relay.

Fog Lamp Switch Circuit Test

  1. Ignition OFF, disconnect the harness connector at the headlamp switch.
  2. Ignition ON, verify the scan tool front fog lamp switch parameter is inactive.
    • If not the specified value, test the signal circuit terminal 7 for a short to ground. If the circuit tests normal, replace the BCM.
  3. Install a 3A fused jumper wire between the signal circuit terminal 7 and the low reference circuit terminal 3. Verify the scan tool front fog lamp 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.
  4. If all circuits test normal, test or replace the headlamp switch.
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