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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 P0645, P0646, or P0647 >> Circuit/System Testing

Circuit/System Testing

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  1. Ignition OFF, disconnect the KR29 Air Conditioning Compressor Relay, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 30 and ground.
    • If the test lamp does not illuminate 

      Replace the X50A Fuse Block - Underhood

    • Go to next step: If the test lamp illuminates 
  3. Ignition ON.
  4. Verify a test lamp illuminates between the ignition circuit terminal 85 and ground.
    • Go to next step: If the test lamp illuminates 
  5. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
  6. Verify the test lamp turns ON and OFF when commanding the ECM Air Conditioning Compressor Clutch Relay On and Off with a scan tool.
    • If the test lamp is always OFF 
    1. Test circuit 459 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. Test circuit 459 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 K20 Engine Control Module
    • If the test lamp is always ON 
    1. Test circuit 459 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 K20 Engine Control Module
    • Go to next step: If the test lamp turns ON and OFF 
  7. Ignition OFF and all vehicle systems OFF, disconnect the connector at the Q2 Air Conditioning Clutch. It may take up to 2 min for all vehicle systems to power down.
  8. Test for less than 10 Ω between the ground circuit terminal 1 and ground.
    • If 10 Ω or greater 

      Repair the open/high resistance on circuit 6450 or the ground connection.

    • Go to next step: If less than 10 Ω 
  9. Connect the KR29 Air Conditioning Compressor Relay.
  10. Connect a test lamp between the Q2 Air Conditioning Clutch control circuit terminal 2 and ground circuit terminal 1, ignition ON.
  11. Verify the test lamp turns ON and OFF when commanding the ECM Air Conditioning Compressor Clutch Relay On and Off with a scan tool.
    • If the test lamp is always OFF and the circuit fuse is good 
    1. Test circuit 59 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 KR29 Air Conditioning Compressor Clutch relay
    • If the test lamp is always OFF and the circuit fuse is open 
    1. Test circuit 59 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 Q2 Air Conditioning Clutch
    • If the test lamp is always ON 
    1. Test circuit 59 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 KR29 Air Conditioning Compressor Clutch relay
    • Go to next step: If the test lamp turns ON and OFF 
  12. Replace the Q2 Air Conditioning Clutch
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