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Circuit/System Testing

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Daytime Running Lamps Malfunction - Z75/X88

  1. Ignition OFF, disconnect the harness connector X4 at the underhood fuse block.
  2. Connect a test lamp between the daytime running lamps relay control circuit terminal H4 and B+.
  3. Ignition ON, command the DRL ON and OFF with a scan tool. The test lamp should turn ON and OFF between the commanded states.
    • If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
    • If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  4. Ignition OFF, reconnect the harness connector X4 at the underhood fuse block.
  5. Disconnect the harness connector at the appropriate daytime running lamp.
  6. Test for less then 5 ohms between the ground circuit listed below and ground.
    • ground circuit terminal B - Z75
    • ground circuit terminal C - X88
    • If less than the specified range, test the ground circuit for an open/high resistance.
  7. Ignition OFF, connect a test lamp between the control circuit terminal A and ground.
  8. Ignition ON, command the DRL ON and OFF with a scan tool. The test lamp should turn ON and OFF.
    • If the test lamp is always ON, test the control circuit for a short to voltage. If the control 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, and the DRL fuse is not open, replace the underhood fuse block.
  9. If all circuits test normal, replace the inoperative daytime running lamp.

Daytime Running Lamps Malfunction - Z88

  1. Ignition OFF, disconnect the harness connector X4 at the underhood fuse block.
  2. Connect a test lamp between the daytime running lamps relay control circuit terminal H4 and B+.
  3. Ignition ON, command the DRL ON and OFF with a scan tool. The test lamp should turn ON and OFF between the commanded states.
    • If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
    • If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  4. Ignition OFF, reconnect the harness connector X4 at the underhood fuse block.
  5. Disconnect the harness connector at the appropriate headlamp.
  6. Test for less then 5 ohms between the ground circuit terminal B and ground.
    • If more than the specified range, test the ground circuit for an open/high resistance.
  7. Ignition OFF, connect a test lamp between the control circuit terminal A and ground.
  8. Ignition ON, command the DRL ON and OFF with a scan tool. The test lamp should turn ON and OFF.
    • If the test lamp is always ON, test the control circuit for a short to voltage. If the control 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, and the DRL fuses are not open, replace the underhood fuse block.
  9. If all circuits test normal, replace the inoperative headlamp.
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