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Home >> Cadillac >> 2018 >> XT5 Platinum >> Repair and Diagnosis >> Accessories & Equipment >> Headlights >> Lighting System - Diagnostic Information And Procedures (DTC B3950 - C0297) >> Diagnostic Information and Procedures >> Trailer Lamps Malfunction (With U4G) >> Circuit/System Testing

Circuit/System Testing

Trailer Backup Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF, disconnect the X1 and X2 harness connectors at the K68 Trailer Lighting Control Module.
  2. Test for less than 5 Ω between the ground circuit terminal 1 X2 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.
    • Go to next step: If less than 5 Ω 
  3. Ignition ON.
  4. Verify a test lamp illuminates between the B+ circuit terminals listed below and ground.
    • Terminal 3 X2
    • Terminal 13 X1
    • If the test lamp does not illuminate 
    1. Ignition OFF, disconnect the appropriate harness connector at the X53A Fuse Block - Rear Body.
    2. Test for infinite resistance between the B+ circuit terminal and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: 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 X53A Fuse Block - Rear Body.
    • Go to next step: If the test lamp illuminates 
  5. Ignition OFF, connect the X1 and X2 harness connectors at the K68 Trailer Lighting Control Module.
  6. Connect a test lamp between the control circuit terminal 8 at the X88 Trailer Connector and ground, ignition ON.
  7. Verify the test lamp turns ON and OFF when commanding the Trailer Backup Lamps 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 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: 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 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 
  8. Test or replace the X88 Trailer Connector.

Trailer Fog Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF, disconnect the X1 and X2 harness connectors at the K68 Trailer Lighting Control Module.
  2. Test for less than 5 Ω between the ground circuit terminal 1 X2 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.
    • Go to next step: If less than 5 Ω 
  3. Ignition ON.
  4. Verify a test lamp illuminates between the B+ circuit terminals listed below and ground.
    • Terminal 3 X2
    • Terminal 13 X1
    • If the test lamp does not illuminate 
    1. Ignition OFF, disconnect the appropriate harness connector at the X53A Fuse Block - Rear Body.
    2. Test for infinite resistance between the B+ circuit terminal and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: 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 X53A Fuse Block - Rear Body.
    • Go to next step: If the test lamp illuminates 
  5. Ignition OFF, connect the X1 and X2 harness connectors at the K68 Trailer Lighting Control Module.
  6. Connect a test lamp between the control circuit terminal 2 at the X88 Trailer Connector and ground, ignition ON.
  7. Verify the test lamp turns ON and OFF when commanding the Trailer Fog Lamp(s) 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 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: 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 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 
  8. Test or replace the X88 Trailer Connector.

Trailer Tail Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF, disconnect the X1 and X2 harness connectors at the K68 Trailer Lighting Control Module.
  2. Test for less than 5 Ω between the ground circuit terminal 1 X2 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.
    • Go to next step: If less than 5 Ω 
  3. Ignition ON.
  4. Verify a test lamp illuminates between the B+ circuit terminals listed below and ground.
    • Terminal 3 X2
    • Terminal 13 X1
    • If the test lamp does not illuminate 
    1. Ignition OFF, disconnect the appropriate harness connector at the X53A Fuse Block - Rear Body.
    2. Test for infinite resistance between the B+ circuit terminal and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: 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 X53A Fuse Block - Rear Body.
    • Go to next step: If the test lamp illuminates 
  5. Ignition OFF, connect the X1 and X2 harness connectors at the K68 Trailer Lighting Control Module.
  6. Connect a test lamp between the appropriate control circuit terminal listed below at the X88 Trailer Connector and ground, ignition ON.
    • Left tail lamp control terminal 7
    • Right tail lamp control terminal 5
  7. 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 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: 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 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 
  8. Test or replace the X88 Trailer Connector.

Trailer Turn Signal Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF, disconnect the X1 and X2 harness connectors at the K68 Trailer Lighting Control Module.
  2. Test for less than 5 Ω between the ground circuit terminal 1 X2 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.
    • Go to next step: If less than 5 Ω 
  3. Ignition ON.
  4. Verify a test lamp illuminates between the B+ circuit terminals listed below and ground.
    • Terminal 3 X2
    • Terminal 13 X1
    • If the test lamp does not illuminate 
    1. Ignition OFF, disconnect the appropriate harness connector at the X53A Fuse Block - Rear Body.
    2. Test for infinite resistance between the B+ circuit terminal and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: 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 X53A Fuse Block - Rear Body.
    • Go to next step: If the test lamp illuminates 
  5. Ignition OFF, connect the X1 and X2 harness connectors at the K68 Trailer Lighting Control Module.
  6. Connect a test lamp between the appropriate control circuit terminal listed below at the X88 Trailer Connector and ground, ignition ON.
    • Left turn signal lamp control terminal 1
    • Right turn signal lamp control terminal 4
  7. Verify the test lamp turns ON and OFF when commanding the appropriate 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 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: 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 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 
  8. Test or replace the X88 Trailer Connector.

Trailer Stop Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF, disconnect the X1 and X2 harness connectors at the K68 Trailer Lighting Control Module.
  2. Test for less than 5 Ω between the ground circuit terminal 1 X2 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.
    • Go to next step: If less than 5 Ω 
  3. Ignition ON.
  4. Verify a test lamp illuminates between the B+ circuit terminals listed below and ground.
    • Terminal 3 X2
    • Terminal 13 X1
    • If the test lamp does not illuminate 
    1. Ignition OFF, disconnect the appropriate harness connector at the X53A Fuse Block - Rear Body.
    2. Test for infinite resistance between the B+ circuit terminal and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: 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 X53A Fuse Block - Rear Body.
    • Go to next step: If the test lamp illuminates 
  5. Ignition OFF, connect the X1 and X2 harness connectors at the K68 Trailer Lighting Control Module.
  6. Connect a test lamp between the control circuit terminal 6 at the X88 Trailer Connector and ground, ignition ON.
  7. Verify the test lamp turns ON and OFF when commanding the Trailer Brake Lamps 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 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: 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 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 
  8. Test or replace the X88 Trailer Connector.
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