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Home >> GMC >> 2018 >> Acadia Denali, FWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 274 (Lighting System - DTC B3891 To DTC C0297 And Diagnostic Information And Procedures) >> Diagnostic Information and Procedures >> DTC B3950 or B3951: Rear Turn Signal Circuits >> 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.

DTC B3950

  1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the E42L Tail Lamp Assembly - Left. It may take up to 2 min for all vehicle systems to power down.
  2. Test for less than 5 Ω between the ground circuit terminal A and ground.
    • If 5 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.
    • If less than 5 Ω 
  3. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON.
    • E42L Tail Lamp Assembly - Left terminal C (without TVN)
    • E42L Tail Lamp Assembly - Left terminal E (with TVN)
  4. Verify the test lamp turns ON and OFF when commanding the Left Rear Turn Signal/Stop Lamp ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the X5 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 X5 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 
  5. Test or replace the E42L Tail Lamp Assembly - Left.

DTC B3951

  1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the E42R Tail Lamp Assembly - Right. It may take up to 2 min for all vehicle systems to power down.
  2. Test for less than 5 Ω between the appropriate ground circuit terminal listed below and ground.
    • E42R Tail Lamp Assembly - Right terminal D (without TVN)
    • E42R Tail Lamp Assembly - Right terminal E (with TVN)
    • If 5 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.
    • If less than 5 Ω 
  3. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON.
    • E42R Tail Lamp Assembly - Right terminal B (without TVN)
    • E42R Tail Lamp Assembly - Right terminal A (with TVN)
  4. Verify the test lamp turns ON and OFF when commanding the Right Rear Turn Signal/Stop 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 
  5. Test or replace the E42R Tail Lamp Assembly - Right.
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