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DTC B2578: Headlight Control Circuit High: Testing

  1. If lighting system diagnostic system check has been performed, go to next step. If lighting system diagnostic system check has not been performed, perform lighting system diagnostic system check. See LIGHTING SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
    2. NOTE: Headlight relay may also be referred to as headlamp relay.
  2. Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). DLC is located below left side of instrument panel, to right of steering column. See Figure . Turn ignition switch to RUN position. While listening to headlight relay, use scan tool to command headlight relay ON and OFF. Headlight relay is located behind left side of instrument panel. See Figure . If relay does not click ON and OFF, go to next step. If relay clicks ON and OFF, go to DIAGNOSTIC AIDS  .
  3. Turn ignition switch to OFF position. Remove headlight relay. Turn ignition switch to RUN position. Using a test light connected to ground, probe headlight relay harness connector terminal A1 (Orange wire). See Figure . Using scan tool, command headlight relay on and off. If test light does not illuminate, go to next step. If test light not illuminates, go to step  5 .
  4. Test Yellow wire between BCM harness connector C3 terminal A11 and headlight relay harness connector terminal C2 for a short to voltage. See Figure and Figure . If a short to voltage is not found, go to step  6 . If a short to voltage is found, repair as necessary. After repair, go to step  7 .
  5. Replace headlight relay. After repair, go to step  7 .
  6. Replace BCM. See BODY CONTROL MODULE  under REMOVAL & INSTALLATION. After repair, go to next step.
  7. Using scan tool, clear DTCs. Operate vehicle within CODE ENABLE CRITERIA  conditions. Using scan tool, retrieve DTCs. If DTC B2578 resets, return to step  2 . If DTC B2578 does not reset, system is okay.
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