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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 >> Headlamps 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/vehicle 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 the ground circuit or ground connection.
    • Go to next step: If the test lamp illuminates 
  3. Ignition ON/vehicle in service mode, test for 7 - 8 V between the appropriate signal circuit terminals and ground:
    • Headlamps ON = Terminal 9
    • Headlamps OFF = Terminal 4
    • High beams = Terminal 7
    • Flash to pass = Terminal 6
    • AUTO high beam assist = Terminal 10
    • If less than 7 V 
    1. Test the appropriate circuit for a short to ground:
      • Headlamps ON = Circuit 103
      • Headlamps OFF = Circuit 306
      • High beams = Circuit 524
      • Flash to pass = Circuit 307
      • AUTO high beam assist = Circuit 3904
      • 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:
      • Headlamps ON = Circuit 103
      • Headlamps OFF = Circuit 306
      • High beams = Circuit 524
      • Flash to pass = Circuit 307
      • AUTO high beam assist = Circuit 3904
      • 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 K9 Body Control Module.
    • Go to next step: If greater than 7 V 
    1. Test the appropriate circuit for a short to voltage:
      • Headlamps ON = Circuit 103
      • Headlamps OFF = Circuit 306
      • High beams = Circuit 524
      • Flash to pass = Circuit 307
      • AUTO high beam assist = Circuit 3904
      • 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 between 7 - 8 V 
  4. Replace the S78 Turn Signal Switch.

Ambient Light Sensor Malfunction

  1. Ignition/vehicle OFF, disconnect the connector at the B10B Sun Load and Ambient Light and Security Indicator Sensor, ignition ON/vehicle in service mode.
  2. Verify a test lamp illuminates between low reference terminal 6 and B+.
    • If the test lamp does not illuminate 
    1. Test circuit 407 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.
    • Go to next step: If the test lamp illuminates 
  3. Test for 4.8 V - 5.2 V between signal circuit terminal 3 and ground.
    • If less than 4.8 V 
    1. Test circuit 278 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 278 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 K9 Body Control Module.
    • Go to next step: If greater than 5.2 V 
    1. Test circuit 278 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 between 4.8 V - 5.2 V 
  4. Replace the B10B Sun Load Temperature and Ambient Light and Security Indicator Sensor.

Headlamps Malfunction - Low Beam

  1. Ignition OFF, exterior lamps OFF, disconnect the connector at the appropriate component:
    • E13LA Front Headlamp - Left
    • E13RA Front Headlamp - Right
  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 on the ground circuit 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/vehicle in service mode.
  4. Verify the test lamp turns ON and OFF when commanding the appropriate Low Beam Command ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Test the appropriate circuit for a short to ground:
      • E13LA Front Headlamp - Left = Circuit 712
      • E13RA Front Headlamp - Right = Circuit 312
      • 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 712
      • E13RA Front Headlamp - Right = Circuit 312
      • 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 712
      • E13RA Front Headlamp - Right = Circuit 312
      • 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 E13 Headlamp Assembly.

Headlamps Malfunction - High Beam

  1. Ignition OFF, exterior lamps OFF, disconnect the connector at the appropriate component:
    • E13LA Front Headlamp - Left
    • E13RA Front Headlamp - Right
  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 on the ground circuit or ground connection.
    • Go to next step: If the test lamp illuminates 
  3. Connect a test lamp between control circuit terminal 3 and ground, ignition On/vehicle in service mode.
  4. Verify the test lamp turns on and off when commanding the appropriate High Beams on and off with a scan tool.
    • If the test lamp is always OFF 
    1. Test the appropriate circuit for a short to ground:
      • E13LA Front Headlamp - Left = Circuit 711
      • E13RA Front Headlamp - Right = Circuit 311
      • 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 711
      • E13RA Front Headlamp - Right = Circuit 311
      • 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 711
      • E13RA Front Headlamp - Right = Circuit 311
      • 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 E13 Headlamp Assembly.
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