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Home >> GMC >> 2021 >> Terrain SL >> Repair and Diagnosis >> External Pages >> Different car >> Section 157 (Lighting System) >> Diagnostic Information and Procedures >> DTC B257A >> Circuit/System Testing
July 1: So it begins. Don't worry, this is not in the correct legal jurisdiction!

Circuit/System Testing

WARNING: This page is about a different car, the 2021 Buick Enclave. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, all doors closed, all accessories OFF, disconnect the harness connector at the S30 Headlamp Switch. It may take up to 2 min for all vehicle systems to power down.
  2. Test for less than 10 Ω between the ground circuit terminal 8 and ground.
    • If 10 Ω or greater 
    1. Ignition OFF.
    2. Test for less than 2 Ω in the ground circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, repair the open/high resistance in the ground connection.
    • Go to next step: If less than 10 Ω 
  3. Ignition ON.
  4. Verify the scan tool Automatic Headlamps Disable Switch parameter is Inactive.
    • If not Inactive 
    1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module.
    2. Test for infinite resistance between the signal circuit terminal 3 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K9 Body Control Module.
    • Go to next step: If Inactive 
  5. Install a 3 A fused jumper wire between the signal circuit terminal 3 and ground.
  6. Verify the scan tool Automatic Headlamps Disable Switch parameter is Active.
    • If not Active 
    1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit terminal 3 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K9 Body Control Module.
    • Go to next step: If Active 
  7. Verify the scan tool Park Lamps Switch parameter is Inactive.
    • If not Inactive 
    1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module.
    2. Test for infinite resistance between the signal circuit terminal 5 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K9 Body Control Module.
    • Go to next step: If Inactive 
  8. Install a 3 A fused jumper wire between the signal circuit terminal 5 and ground.
  9. Verify the scan tool Park Lamps Switch parameter is Active.
    • If not Active 
    1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit terminal 5 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K9 Body Control Module.
    • Go to next step: If Active 
  10. Verify the scan tool Headlamps On Switch parameter is Inactive.
    • If not Inactive 
    1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module.
    2. Test for infinite resistance between the signal circuit terminal 1 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K9 Body Control Module.
    • Go to next step: If Inactive 
  11. Install a 3 A fused jumper wire between the signal circuit terminal 1 and ground.
  12. Verify the scan tool Headlamps On Switch parameter is Active.
    • If not Active 
    1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit terminal 1 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K9 Body Control Module.
    • Go to next step: If Active 
  13. Test or replace the S30 Headlamp Switch.
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