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Circuit/System Testing

WARNING: This page is about a different car, the 2009 GMC Canyon and 2009 Chevrolet Colorado. However, it is still accessible from the selected car via links, so may be relevant.

Headlamp Relay Control Circuit Test

  1. Ignition OFF, disconnect the HDLP relay.
  2. Connect a test lamp between the relay control circuit terminal 86 and B+.
  3. Ignition ON, command the headlamps 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 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. If all circuits test normal, test or replace the relay.
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