LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Cadillac >> 2019 >> XT5 Base, FWD >> Repair and Diagnosis (Single Page) >> Accessories & Equipment >> Headlights >> Lighting System - Diagnostic Information And Procedures (2 Of 2) >> Diagnostic Information and Procedures >> DTC B3950 or B3951 (Trailer Lighting Control Module) >> Circuit/System Testing
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Circuit/System Testing

DTC B3950

  1. Ignition OFF, disconnect the harness connector at the X88 Trailer Connector.
  2. Connect a test lamp between the control circuit terminal 1 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.
      • Go to next step: 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.
    • Go to next step: If the test lamp turns ON and OFF 
  4. Replace the X88 Trailer Connector.

DTC B3951

  1. Ignition OFF, disconnect the harness connector at the X88 Trailer Connector.
  2. Connect a test lamp between the control circuit terminal 4 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.
      • Go to next step: 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.
    • Go to next step: If the test lamp turns ON and OFF 
  4. Replace the X88 Trailer Connector.
scientia non olet · About LEMON Manuals