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Home >> Cadillac >> 2021 >> CT4 Sport, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 231 (HVAC - Automatic) >> Diagnostic Information and Procedures >> DTC P0535, P0537, P0538, or P153B (L3B, LSY) >> 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, disconnect the harness connector at the B39 Air Conditioning Evaporator Air Temperature Sensor. It may take up to 10 min for all vehicle systems to power down.
    2. NOTE:

    The scan tool must be disconnected from the vehicle before performing the next test.

  2. Test for less than 10 Ω between the low reference circuit terminal 1 and ground.
    • If 10 Ω or greater 
    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 less than 10 Ω 
  3. Ignition ON/Vehicle in Service Mode. Test for 4.8 - 5.2 V between the signal circuit terminal 2 and ground.
    • If less than 4.8 V 
    1. Test circuit 6137 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 6137 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
    • If greater than 5.2 V 
    1. Test circuit 6137 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 - 5.2 V 
  4. Test or replace the B39 Air Conditioning Evaporator Air Temperature Sensor.
  5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
  6. Verify the DTC does not set.
    • If the DTC sets 

      Replace the K9 Body Control Module.

    • Go to next step: If the DTC does not set 
  7. All OK
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