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Home >> Cadillac >> 2021 >> CT4 Sport, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 224 (Lighting System - Diagnostic Information And Procedures (1 Of 2)) >> Diagnostic Information and Procedures >> DTC B15A8 >> Circuit/System Testing

Circuit/System Testing

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    NOTE:

    Each component may need to be disconnected to isolate a short to voltage, short to ground, or an open/high resistance. Use the schematics to identify the following:

    • Courtesy lamps the vehicle is equipped with
    • Each component's control and ground circuit terminals
    • Component locations on control circuit 4783 
  1. Set the S36 Dimmer Switch to full intensity.
  2. Ignition OFF, disconnect the X7 and X5 connector at the K9 Body Control Module, ignition ON:
  3. Verify the accent/courtesy lamps are not illuminated:
    • E8VB Rear Floor Courtesy Lamp - Left
    • E8VD Rear Floor Courtesy Lamp - Right
    • If an accent/courtesy lamp is illuminated 

      Repair the short to voltage on circuit 4783.

    • Go to next step: If all accent/courtesy lamps are not illuminated 
  4. Connect a 3 A fused jumper wire between B+ and circuit terminal 24 at the X7 connector.
  5. Verify the accent/courtesy lamps are illuminated.
    • If an accent/courtesy lamp is not illuminated and the jumper fuse is OK. 
    1. Test the appropriate circuit for an open/high resistance:
      • E8VB Rear Floor Courtesy Lamp - Left - 2150
      • E8VD Rear Floor Courtesy Lamp - Right - 2150
      • If an open/high resistance is found, repair the fault on the circuit or ground connection.
      • Go to next step: If an open/high resistance is not found.
    2. Test circuit 4783 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 appropriate accent/courtesy lamp.
    • If the accent/courtesy lamp is not illuminated and the jumper fuse is open 
    1. Test circuit 4783 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 appropriate accent/courtesy lamp.
    • Go to next step: If the accent/courtesy lamps are illuminated 
  6. Replace the K9 Body Control Module.
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