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Home >> GMC >> 2011 >> Terrain SLT, 2.4 C, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 178 (Lighting System) >> Diagnostic Information and Procedures >> DTC B257A >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2010 GMC Terrain and 2010 Chevrolet Equinox. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the X1 harness connector at the S78 Turn Signal/Multi-Function Switch.
  2. Ignition OFF, test for less than 5 Ω between the ground circuit terminal 6 and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Park Lamps Switch parameter is Inactive.
    • If not the specified value, test the signal circuit terminal 7 for a short to ground. If the circuit tests normal, replace the K9 BCM.
  4. Install a 3 A fused jumper wire between the signal circuit terminal 7 and the ground circuit terminal 6. Verify the scan tool Park Lamps Switch parameter is Active.
    • If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 BCM.
  5. Verify the scan tool Headlamps On Switch parameter is Inactive.
    • If not the specified value, test the signal circuit terminal 2 for a short to ground. If the circuit tests normal, replace the K9 BCM.
  6. Install a 3 A fused jumper wire between the signal circuit terminal 2 and the ground circuit terminal 6. Verify the scan tool Headlamps On Switch is Active.
    • If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 BCM.
  7. Verify the scan tool Automatic Headlamps Disable Switch parameter is Inactive.
    • If not the specified value, test the signal circuit terminal 9 for a short to ground. If the circuit tests normal, replace the K9 BCM.
  8. Install a 3 A fused jumper wire between the signal circuit terminal 9 and the ground circuit terminal 6. Verify the scan tool Automatic Headlamps Disable Switch is Active.
    • If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 BCM.
  9. If all circuits test normal, test or replace the S78 Turn Signal/Multi-Function Switch.
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