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Home >> GMC >> 2006 >> Sierra 1500 HD, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 981 (Lighting Systems) >> Diagnostic Information and Procedures >> Daytime Running Lamps Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Ambient Light Sensor Circuit Test

  1. Ignition OFF, disconnect the harness connector at the ambient light sensor.
  2. Ignition OFF, test for less than 1 ohm of resistance between the listed ground circuit terminal and ground.
    • Ambient light sensor terminal B
    • Ambient light/sunload sensor terminal C
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool ambient light sensor parameter is greater than 4.5 volts.
    • If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the BCM.
  4. Install a 3A fused jumper wire between the listed signal circuit terminal and the low reference circuit terminal. Verify the scan tool light sensor parameter is less than 1.0 volt.
    • Ambient light sensor terminal A to B
    • Ambient light/sunload sensor terminal D to C
    • If greater than the specified range, 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 ambient light sensor.

DRL Relay Control Circuit Test

  1. Ignition OFF, disconnect the harness connector X4 at the BCM.
  2. Ignition ON, verify the daytime running lamps are not on.
    • If the daytime running lamps are on, test the DRL relay control circuit for a short to ground. If the circuit tests normal replace the underhood fuse block.
  3. Install a 10A fused jumper wire between the relay control circuit terminal 23 and ground. Verify the daytime running lamps are on. are on.
    • If the daytime running lamps are not on, test the DRL relay control circuit for an open/high resistance. If the circuit tests normal replace the underhood fuse block.
  4. If all circuits test normal, replace the BCM.

Daytime Running Lamps Circuit Test

  1. Ignition OFF, disconnect the harness connector at the affected headlamp.
  2. Test for less than 1 ohm of resistance between the ground circuit terminal B and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the control circuit terminal A and the ground circuit terminal B.
  4. Command the daytime running 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 underhood fuse block.
    • 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 underhood fuse block.
  5. If all circuits test normal, test or replace the affected headlamp.
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