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Home >> Cadillac >> 2007 >> Escalade EXT >> Repair and Diagnosis >> External Pages >> Different car >> Section 1810 (Lighting System) >> Diagnostic Information and Procedures >> DTC B257A >> Circuit/System Testing
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Circuit/System Testing

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  1. Ignition OFF, disconnect the X2 harness connector at the BCM.
  2. Connect a test lamp between B+ and the signal circuit terminal 17.
  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 and panel dimmer 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 and panel dimmer switch.
  4. Connect a test lamp between B+ and the signal circuit terminal 3.
  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 and panel dimmer 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 and panel dimmer switch.
  6. If all circuits test normal, replace the BCM.
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