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Home >> GMC >> 2018 >> Acadia Denali, FWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 271 (Lighting System - DTC B0655 To DTC B3890) >> Diagnostic Information and Procedures >> DTC B0655: Brake Lamp Switch Circuit Not Plausible >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2017 Cadillac ATS. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, exterior lamps OFF, disconnect the harness connectors at the following components.
    • E6 Center High Mounted Stop Lamp
    • K68 Trailer Lighting Control Module
  2. Connect a test lamp between the control circuit terminal 14 and ground, ignition ON.
  3. Verify the test lamp turns ON and OFF when commanding the Center Brake Lamp ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the X4 harness connector at the K9 Body Control Module.
    2. Test for infinite resistance between the control circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance
    3. Test for less than 2 Ω in the control 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.
    • If the test lamp is always ON 
    1. Ignition OFF, disconnect the X4 harness connector at the K9 Body Control Module, ignition ON.
    2. Test for less than 1 V between the control circuit terminal and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the K9 Body Control Module.
    • If the test lamp turns ON and OFF 
  4. Ignition OFF.
  5. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON.
    • Terminal A - sedan
    • Terminal 1 - coupe
  6. Verify the test lamp turns ON and OFF when commanding the Center Brake Lamp ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the X4 harness connector at the K9 Body Control Module.
    2. Test for infinite resistance between the control circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance
    3. Test for less than 2 Ω in the control 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.
    • If the test lamp turns ON and OFF 
  7. Ignition OFF, connect the harness connector at the E6 Center High Mounted Stop Lamp, ignition ON.
  8. Verify the center high mounted stop lamp turns ON and OFF when commanding the Center Brake Lamp ON and OFF with a scan tool.
    • If the center high mounted stop lamp is always OFF 

      Test or replace the E6 Center High Mounted Stop Lamp.

    • If the center high mounted stop lamp turns ON and OFF 
  9. Test or replace the K68 Trailer Lighting Control Module.
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