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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 B3885 or B3886: Trailer Left Tail Lamp >> 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 B3885

  1. Ignition OFF.
  2. Connect a test lamp between the left trailer tail lamp control circuit (5184 BN/GY) at the W8 Blunt Cut Trailer Provision and ground, ignition ON.
  3. Verify the test lamp turns ON and OFF when commanding the Left Trailer Tail Lamp ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the X1 harness connector at the K68 Trailer Lighting Control Module.
    2. Test for infinite resistance between the control circuit terminal and ground.
      • If less than infinite resistance, repair the short to ground on the circuits.
      • If infinite resistance
    3. Test for less than 2 Ω in the control circuits end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K68 Trailer Lighting Control Module.
    • If the test lamp is always ON 
    1. Ignition OFF, disconnect the X1 harness connector at the K68 Trailer Lighting 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 K68 Trailer Lighting Control Module.
    • If the test lamp turns ON and OFF 
  4. Test or replace the W8 Blunt Cut Trailer Provision.

DTC B3886

  1. Ignition OFF.
  2. Connect a test lamp between the right trailer tail lamp control circuit (5185 GY) at the W8 Blunt Cut Trailer Provision and ground, ignition ON.
  3. Verify the test lamp turns ON and OFF when commanding the Right Trailer Tail Lamp ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the X1 harness connector at the K68 Trailer Lighting Control Module.
    2. Test for infinite resistance between the control circuit terminal and ground.
      • If less than infinite resistance, repair the short to ground on the circuits.
      • If infinite resistance
    3. Test for less than 2 Ω in the control circuits end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K68 Trailer Lighting Control Module.
    • If the test lamp is always ON 
    1. Ignition OFF, disconnect the X1 harness connector at the K68 Trailer Lighting 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 K68 Trailer Lighting Control Module.
    • If the test lamp turns ON and OFF 
  4. Test or replace the W8 Blunt Cut Trailer Provision.
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