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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 >> Park, License, and/or Tail Lamps Malfunction >> Circuit/System Testing

Circuit/System Testing

Turn Signal/Multifunction Switch Malfunction

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, open and close drivers door, disconnect the harness connector at the S78 Turn Signal/Multifunction Switch. It may take up to 2 min for all vehicle systems to power down.
  2. Test for less than 10 Ω between the ground circuit terminal 3 and ground.
    • If 10 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 10 Ω 
  3. Ignition ON.
  4. Verify the scan tool Park Lamps Switch parameter is Inactive.
    • If not Inactive 
    1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module.
    2. Test for infinite resistance between the signal circuit terminal 5 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K9 Body Control Module.
    • Go to next step: If Inactive 
  5. Install a 3 A fused jumper wire between the signal circuit terminal 5 and ground.
  6. Verify the scan tool Park Lamps Switch parameter is Active.
    • If not Active 
    1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit terminal 5 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the signal 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.
    • Go to next step: If Active 
  7. Test or replace the S78 Turn Signal/Multifunction Switch.

Park Lamps Malfunction (with T4A)

  1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 2 and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition OFF, remove the F21DA fuse at the X51A Fuse Block - Instrument Panel.
    2. Test for less than 2 Ω in the B+ circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Ignition OFF, remove the F21DA fuse at the X51A Fuse Block - Instrument Panel.
    2. Test for infinite resistance between the B+ circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K9 Body Control Module.
    • Go to next step: If the test lamp illuminates 
  3. Ignition OFF, connect the X1 harness connector at the K9 Body Control Module.
  4. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate component listed below. It may take up to 2 min for all vehicle systems to power down.
    • E2LF Side Marker Lamp - Left Front (with TU2)
    • E2RF Side Marker Lamp - Right Front (with TU2)
    • E42L Tail Lamp Assembly - Left
    • E42R Tail Lamp Assembly - Right
    • E69L Multifunction Lamp Assembly - Front Fascia Left (T4L - TR7)
    • E69R Multifunction Lamp Assembly - Front Fascia Right (T4L - TR7)
  5. Test for less than 5 Ω between the appropriate ground circuit terminal listed below and ground.
    • E2LF Side Marker Lamp - Left Front terminal 1 (with TU2)
    • E2RF Side Marker Lamp - Right Front terminal 1 (with TU2)
    • E42L Tail Lamp Assembly - Left terminal 5
    • E42R Tail Lamp Assembly - Right terminal 5
    • E69L Multifunction Lamp Assembly - Front Fascia Left terminal 4 (T4L without TR7)
    • E69R Multifunction Lamp Assembly - Front Fascia Right terminal 4 (T4L without TR7)
    • 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 
  6. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON.
    • E2LF Side Marker Lamp - Left Front terminal 2 (with TU2)
    • E2RF Side Marker Lamp - Right Front terminal 2 (with TU2)
    • E42L Tail Lamp Assembly - Left terminal 2
    • E42R Tail Lamp Assembly - Right terminal 2
    • E69L Multifunction Lamp Assembly - Front Fascia Left terminal 5 (T4L without TR7)
    • E69R Multifunction Lamp Assembly - Front Fascia Right terminal 5 (T4L without TR7)
  7. Verify the test lamp turns ON and OFF when commanding the appropriate Park Lamps 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.
      • 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 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.
    • Go to next step: If the test lamp turns ON and OFF 
  8. Test or replace the park/side marker/tail lamp.

Park Lamps Malfunction (with T4L)

  1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 2 and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition OFF, remove the F21DA fuse at the X51A Fuse Block - Instrument Panel.
    2. Test for less than 2 Ω in the B+ circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Ignition OFF, remove the F21DA fuse at the X51A Fuse Block - Instrument Panel.
    2. Test for infinite resistance between the B+ circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K9 Body Control Module.
    • Go to next step: If the test lamp illuminates 
  3. Ignition OFF, connect the X1 harness connector at the K9 Body Control Module.
  4. Disconnect the KR50 Headlamp Relay.
  5. Verify a test lamp illuminates between the B+ circuit terminal 85 and ground.
    • If the test lamp does not illuminate 

      Replace the X50A Fuse Block - Underhood.

    • Go to next step: If the test lamp illuminates 
  6. Verify a test lamp illuminates between the B+ circuit terminal 30 and ground.
    • If the test lamp does not illuminate 

      Replace the X50A Fuse Block - Underhood.

    • Go to next step: If the test lamp illuminates 
  7. Connect a test lamp between the control circuit terminal 86 and B+, ignition ON.
  8. Verify the test lamp turns ON and OFF when commanding the headlamps ON and OFF with the S78 Turn Signal/Multifunction Switch.
    • If the test lamp is always OFF 
    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 13 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Ignition OFF.
    4. 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.
    2. Test for infinite resistance between the control circuit terminal 13 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K9 Body Control Module.
    • Go to next step: If the test lamp turns ON and OFF 
  9. Ignition OFF, connect the KR50 Headlamp Relay.
  10. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate component listed below. It may take up to 2 min for all vehicle systems to power down.
    • E2LF Side Marker Lamp - Left Front (with TU2)
    • E2RF Side Marker Lamp - Right Front (with TU2)
    • E42L Tail Lamp Assembly - Left
    • E42R Tail Lamp Assembly - Right
    • E69L Multifunction Lamp Assembly - Front Fascia Left (T4L - TR7)
    • E69R Multifunction Lamp Assembly - Front Fascia Right (T4L - TR7)
  11. Test for less than 5 Ω between the appropriate ground circuit terminal listed below and ground.
    • E2LF Side Marker Lamp - Left Front terminal 1 (with TU2)
    • E2RF Side Marker Lamp - Right Front terminal 1 (with TU2)
    • E42L Tail Lamp Assembly - Left terminal 5
    • E42R Tail Lamp Assembly - Right terminal 5
    • E69L Multifunction Lamp Assembly - Front Fascia Left terminal 4 (T4L without TR7)
    • E69R Multifunction Lamp Assembly - Front Fascia Right terminal 4 (T4L without TR7)
    • 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 
  12. Connect a test lamp between the control circuit terminal 5 and ground, ignition ON.
  13. Verify the test lamp turns ON and OFF when commanding the headlamps ON and OFF with the S78 Turn Signal/Multifunction Switch.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the X5 harness connector at the X50A Fuse Block - Underhood.
    2. Test for infinite resistance between the control circuit terminal 5 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 KR50 Headlamp Relay.
    • If the test lamp is always ON 
    1. Ignition OFF, disconnect the X5 harness connector at the X50A Fuse Block - Underhood, ignition ON.
    2. Test for less than 1 V between the control circuit terminal 5 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the KR50 Headlamp Relay.
    • Go to next step: If the test lamp turns ON and OFF 
  14. Ignition OFF.
  15. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON.
    • E2LF Side Marker Lamp - Left Front terminal 2 (with TU2)
    • E2RF Side Marker Lamp - Right Front terminal 2 (with TU2)
    • E42L Tail Lamp Assembly - Left terminal 2
    • E42R Tail Lamp Assembly - Right terminal 2
    • E69L Multifunction Lamp Assembly - Front Fascia Left terminal 5 (T4L without TR7)
    • E69R Multifunction Lamp Assembly - Front Fascia Right terminal 5 (T4L without TR7)
  16. Verify the test lamp turns ON and OFF when commanding the appropriate Park Lamps 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.
      • 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 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.
    • Go to next step: If the test lamp turns ON and OFF 
  17. Test or replace the park/side marker/tail lamp.

License Plate Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF, disconnect the appropriate components listed below. It may take up to 2 min for all vehicle systems to power down.
    • E7L License Plate Lamp - Left (with TC2)
    • E7R License Plate Lamp - Right (with TC2)
    • S46B Liftgate Unlatch Switch (with TB5)
  2. Test for less than 5 Ω between each ground circuit terminal listed below and ground.
    • E7L License Plate Lamp - Left terminal 2 (with TC2)
    • E7R License Plate Lamp - Right terminal 2 (with TC2)
    • S46B Liftgate Unlatch Switch terminal 1 (with TB5)
    • 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. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON.
    • E7L License Plate Lamp - Left terminal 1 (with TC2)
    • E7R License Plate Lamp - Right terminal 1 (with TC2)
    • S46B Liftgate Unlatch Switch terminal 3 (with TB5)
  4. Verify the test lamp turns ON and OFF when commanding the License Plate Lamps ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the X7 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.
      • 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 K9 Body Control Module.
    • If the test lamp is always ON 
    1. Ignition OFF, disconnect the X7 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.
    • Go to next step: If the test lamp turns ON and OFF 
  5. Test or replace the inoperative component.
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