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Home >> Cadillac >> 2021 >> CT4 Sport, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 87 (Lighting System - Diagnostic Information And Procedures (2 Of 2)) >> Diagnostic Information and Procedures >> Park, License, and/or Tail Lamps Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2022 Cadillac CT4. However, it is still accessible from the selected car via links, so may be relevant.

Turn Signal Switch Malfunction

  1. Ignition OFF, disconnect the connector at the S78 Turn Signal Switch.
  2. Verify a test lamp illuminates between ground circuit terminal 3 and B+:
    • If the test lamp does not illuminate 
    1. Repair the open/high resistance on circuit 1750 or ground connection.
    • Go to next step: If the test lamp illuminates 
  3. Ignition ON, verify the scan tool Park Lamps Switch parameter is Inactive.
    • If not Inactive 
    1. Test circuit 13 for a short to ground.
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short to ground is not found.
    2. Replace the K9 Body Control Module.
    • Go to next step: If Inactive 
  4. Install a 3 A fused jumper wire between the signal circuit terminal 5 and ground.
  5. Verify the scan tool Park Lamps Switch parameter is Active.
    • If not Active and the 3 A fuse is OK 
    1. Test circuit 13 for an open/high resistance.
      • If an open/high resistance is found, repair the fault on the circuit.
      • Go to next step: If an open/high resistance is not found.
    2. Replace the K9 Body Control Module.
    • If not Active and the 3 A fuse is open 
    1. Test circuit 13 for a short to voltage.
      • If a short to voltage is found, repair the fault on the circuit.
      • Go to next step: If a short to voltage is not found.
    2. Replace the K9 Body Control Module.
    • Go to next step: If Active 
  6. Test or replace the S78 Turn Signal Switch.

Park Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF, disconnect the connector at the appropriate park/tail lamp:
    • E13LA Front Headlamp - Left
    • E13RA Front Headlamp - Right
    • E5E Tail Lamp - Left
    • E5F Tail Lamp - Right
  2. Verify a test lamp illuminates between the appropriate ground circuit terminal and B+:
    • E13 Headlamp Assembly = Terminal 2
    • E5 Tail Lamp = Terminal 1
    • If the test lamp does not illuminate 
    1. Repair the open/high resistance on the ground circuit or ground connection.
    • Go to next step: If the test lamp illuminates 
  3. Connect a test lamp between the appropriate control circuit terminal and ground, ignition ON:
    • E13 Headlamp Assembly = Terminal 7
    • E5 Tail Lamp = Terminal 3
  4. Verify the test lamp turns ON and OFF when commanding the appropriate lamp ON and OFF with a scan tool:
    • Left Front Park Lamp
    • Right Front Park Lamp
    • Left Tail Lamp
    • Right Tail Lamp
    • If the test lamp is always OFF 
    1. Test the appropriate circuit for a short to ground:
      • E13LA Front Headlamp - Left = Circuit 1254
      • E13RA Front Headlamp - Right = Circuit 1253
      • E5E Tail Lamp - Left = Circuit 6993
      • E5F Tail Lamp - Right = Circuit 6995
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short to ground is not found
    2. Test the appropriate circuit for an open/high resistance:
      • E13LA Front Headlamp - Left = Circuit 1254
      • E13RA Front Headlamp - Right = Circuit 1253
      • E5E Tail Lamp - Left = Circuit 6993
      • E5F Tail Lamp - Right = Circuit 6995
      • If an open/high resistance is found, repair the fault on the circuit.
      • Go to next step: If an open/high resistance is not found
    3. Replace the K219 Lighting Control Module.
    • If the test lamp is always ON 
    1. Test the appropriate circuit for a short to voltage:
      • E13LA Front Headlamp - Left = Circuit 1254
      • E13RA Front Headlamp - Right = Circuit 1253
      • E5E Tail Lamp - Left = Circuit 6993
      • E5F Tail Lamp - Right = Circuit 6995
      • If a short to voltage is found, repair the fault on the circuit.
      • Go to next step: If a short to voltage is not found
    2. Replace the K219 Lighting Control Module.
    • Go to next step: If the test lamp turns ON and OFF 
  5. Replace the appropriate park/tail lamp.

License Plate Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF, disconnect the connector at the Liftgate Handle Switch/License Plate Lamp.
  2. Verify a test lamp illuminates between ground circuit terminal 1 and B+.
    • If the test lamp does not illuminate 
    1. Repair the open/high resistance circuit 850 or ground connection.
    • Go to next step: If the test lamp illuminates 
  3. Connect a test lamp between control circuit terminal 2 and ground, ignition ON.
  4. Verify the test lamp turns ON and OFF when commanding the License Plate Lamp ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Test circuit 6846 for a short to ground.
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short to ground is not found
    2. Test circuit 6846 for an open/high resistance.
      • If an open/high resistance is found, repair the fault on the circuit.
      • Go to next step: If an open/high resistance is not found
    3. Replace the K219 Lighting Control Module.
    • If the test lamp is always ON 
    1. Test circuit 6846 for a short to voltage.
      • If a short to voltage is found, repair the fault on the circuit.
      • Go to next step: If a short to voltage is not found.
    2. Replace the K219 Lighting Control Module.
    • Go to next step: If the test lamp turns ON and OFF 
  5. Replace the License Plate Lamp.
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