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Home >> Cadillac >> 2012 >> Escalade EXT >> Repair and Diagnosis >> External Pages >> Different car >> Section 1419 (Lighting System) >> Diagnostic Information and Procedures >> DTC B257A >> Circuit/System Testing
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Circuit/System Testing

WARNING: This page is about a different car, the 2009 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the X2 harness connector at the BCM.
  2. Connect a test lamp between the signal circuit terminal 17 and B+.
  3. Turn the headlamp switch between the AUTO and AUTO disable positions. The test lamp should turn ON and OFF as the switch is cycled.
    • If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit test normal, replace the headlamp switch.
    • If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the headlamp switch.
  4. Connect a test lamp between the signal circuit terminal 12 and B+.
  5. Turn the headlamp switch to the ON and OFF positions. The test lamp should turn ON and OFF as the switch is cycled.
    • If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit test normal, replace the headlamp switch.
    • If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the headlamp switch.
  6. Connect a test lamp between the signal circuit terminal 8 and B+.
  7. Turn the headlamp switch to the PARK and OFF positions. The test lamp should turn ON and OFF as the switch is cycled.
    • If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit test normal, replace the headlamp switch.
    • If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the headlamp switch.
  8. If all circuits test normal, replace the BCM.
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