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Home >> Cadillac >> 2007 >> Escalade EXT >> Repair and Diagnosis >> External Pages >> Different car >> Section 1344 (Lighting Systems) >> 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 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. 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 B+ and the signal circuit terminal 17.
  3. Turn the headlamp switch between the headlamp AUTO and headlamp 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 tests normal, replace the headlamp switch.
    • If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit tests normal, replace the headlamp switch.
  4. Connect a test lamp between B+ and the signal circuit terminal 12.
  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 tests normal, replace the headlamp switch.
    • If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit tests normal, replace the headlamp switch.
  6. If all circuits test normal, replace the BCM.
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