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Home >> Chevrolet >> 2007 >> Uplander Base, 3.9 1 >> Repair and Diagnosis >> External Pages >> Different car >> Section 14 (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 2007 Chevrolet Monte Carlo and 2007 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
  1. Headlamp switch to OFF, disconnect the BCM connector C2.
  2. Ignition to ON, connect a test lamp between the headlamp OFF switch circuit and the positive battery terminal. Verify the test lamp illuminates.
    • If the test lamp does not illuminate:
      • Test for a short to voltage or an open in the headlamp OFF switch circuit.
      • Test for an open in the headlamp ground circuit.
      • If the circuit/connections test normal replace the headlamp switch.
  3. Headlamp switch to PARK. Verify the test lamp is not illuminated.
    • If the test lamp illuminates, test for a short to ground in the headlamp OFF switch circuit. If the circuit/connections test normal, replace the headlamp switch.
  4. Headlamp switch to PARK. Connect a test lamp between the park lamp switch ON circuit and the positive battery terminal. Verify the test lamp illuminates.
    • If the test lamp does not illuminate, test for a short to voltage or an open in the park lamp switch ON circuit. If the circuit/connections test normal, replace the headlamp switch.
  5. Headlamp switch to OFF, verify the test lamp does not illuminate.
    • If the test lamp does illuminate, test for a short to ground in the park lamp switch ON circuit. If the circuit/connections test normal, replace the headlamp switch.
  6. If the circuit/connections test normal, replace the BCM.
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