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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 >> Backup 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.
  1. Ignition/vehicle OFF, exterior lamps OFF, disconnect the appropriate lamp assembly:
    • E42L Rear Body Structure Stop Lamp - Left
    • E42R Rear Body Structure Stop Lamp - Right
  2. Verify a test lamp illuminates between the appropriate ground circuit terminal and B+:
    • E42L Rear Body Structure Stop Lamp - Left = Terminal 6
    • E42R Rear Body Structure Stop Lamp - Right = 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/vehicle in service mode.
    • E42L Rear Body Structure Stop Lamp - Left = Terminal 2
    • E42R Rear Body Structure Stop Lamp - Right = Terminal 5
  4. Verify the test lamp turns ON and OFF when commanding the Backup Lamps ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Test the appropriate circuit for short to ground:
      • E42L Rear Body Structure Stop Lamp - Left = Circuit 24
      • E42R Rear Body Structure Stop Lamp - Right = Circuit 1324
      • 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:
      • E42L Rear Body Structure Stop Lamp - Left = Circuit 24
      • E42R Rear Body Structure Stop Lamp - Right = Circuit 1324
      • 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:
      • E42L Rear Body Structure Stop Lamp - Left = Circuit 24
      • E42R Rear Body Structure Stop Lamp - Right = Circuit 1324
      • 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 E42 Rear Body Structure Stop Lamp.
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