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Home >> Cadillac >> 2017 >> XT5 Base >> Repair and Diagnosis (Single Page) >> Accessories & Equipment >> Headlights >> Lighting System - DTC B3950 To DTC C0297 And Diagnostic Information And Procedures >> Diagnostic Information and Procedures >> DTC B3950 or B3951: Trailer Left/Right Turn Signal Lamp (Trailer Lighting Control Module) >> Circuit/System Testing
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Circuit/System Testing

DTC B3950

  1. Ignition OFF.
  2. Connect a test lamp between the control circuit terminal 1 at the X88 Trailer Connector and ground, ignition ON.
  3. Verify the test lamp turns ON and OFF when commanding the Left Trailer Turn Signal 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. Replace the X88 Trailer Connector.

DTC B3951

  1. Ignition OFF.
  2. Connect a test lamp between the control circuit terminal 4 at the X88 Trailer Connector and ground, ignition ON.
  3. Verify the test lamp turns ON and OFF when commanding the Right Trailer Turn Signal 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. Replace the X88 Trailer Connector.
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