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Home >> Cadillac >> 2021 >> CT4 Sport, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 338 (Lighting System - Diagnostic Information And Procedures (2 Of 2)) >> Diagnostic Information and Procedures >> Daytime Running Lamps Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2022 Cadillac CT5. However, it is still accessible from the selected car via links, so may be relevant.

Ambient Light Sensor Malfunction

  1. Ignition/vehicle OFF, disconnect the connector at the B10B Sun Load Temperature and Ambient Light and Security Indicator Sensor, ignition ON.
  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.

Daytime Running Lamps Malfunction

  1. Ignition/vehicle OFF, exterior lamps OFF, disconnect the appropriate component:
    • {With T87} E13LA Front Headlamp - Left
    • {With T87} E13RA Front Headlamp - Right
    • {With T87} E4A Cornering Lamp - Left
    • {With T87} E4B Cornering Lamp - Right
    • {Without T87} E4C Daytime Running Lamp - Left
    • {Without T87} E4D Daytime Running Lamp - Right
  2. Verify a test lamp illuminates between the appropriate ground circuit terminal and B+:
    • {With T87} E13LA Front Headlamp - Left = Terminal 7
    • {With T87} E13RA Front Headlamp - Right = Terminal 7
    • {With T87} E4A Cornering Lamp - Left = Terminal 1
    • {With T87} E4B Cornering Lamp - Right = Terminal 1
    • {Without T87} E4C Daytime Running Lamp - Left = Terminal 1
    • {Without T87} E4D Daytime Running 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:
    • {With T87} E13LA Front Headlamp - Left = Terminal 6
    • {With T87} E13RA Front Headlamp - Right = Terminal 6
    • {With T87} E4A Cornering Lamp - Left = Terminal 2
    • {With T87} E4B Cornering Lamp - Right = Terminal 2
    • {Without T87} E4C Daytime Running Lamp - Left = Terminal 2
    • {Without T87} E4D Daytime Running Lamp - Right = Terminal 2
  4. Verify the test lamp turns ON and OFF while commanding the appropriate Daytime Running Lamp ON and OFF with the scan tool.
    • If the test lamp is always OFF 
    1. Test the appropriate circuit for a short to ground:
      • {With T87} E13LA Front Headlamp - Left = Circuit 7538
      • {With T87} E13RA Front Headlamp - Right = Circuit 7539
      • {With T87} E4A Cornering Lamp - Left = Circuit 2745
      • {With T87} E4B Cornering Lamp - Right = Circuit 2745
      • {Without T87} E4C Daytime Running Lamp - Left = Circuit 7538
      • {Without T87} E4D Daytime Running Lamp - Right = Circuit 7539
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short tot ground is not found
    2. Test for the appropriate circuit for an open/high resistance:
      • {With T87} E13LA Front Headlamp - Left = Circuit 7538
      • {With T87} E13RA Front Headlamp - Right = Circuit 7539
      • {With T87} E4A Cornering Lamp - Left = Circuit 2745
      • {With T87} E4B Cornering Lamp - Right = Circuit 2745
      • {Without T87} E4C Daytime Running Lamp - Left = Circuit 7538
      • {Without T87} E4D Daytime Running Lamp - Right = Circuit 7539
      • 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:
      • {With T87} E13LA Front Headlamp - Left = Circuit 7538
      • {With T87} E13RA Front Headlamp - Right = Circuit 7539
      • {With T87} E4A Cornering Lamp - Left = Circuit 2745
      • {With T87} E4B Cornering Lamp - Right = Circuit 2745
      • {Without T87} E4C Daytime Running Lamp - Left = Circuit 7538
      • {Without T87} E4D Daytime Running Lamp - Right = Circuit 7539
      • 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 lamp assembly with the inoperative daytime running lamp.
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