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Home >> Chevrolet >> 2017 >> Spark LT, Automatic CVT Trans >> Repair and Diagnosis >> External Pages >> Different car >> Section 38 (HVAC System - Automatic) >> Diagnostic Information and Procedures >> DTC P0645, P0646, or P0647 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2019 Buick Cascada, 2018 Buick Cascada, and 2017 Buick Cascada. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, and all vehicle systems OFF. Disconnect the harness connector at the Q2 A/C Compressor Clutch. It may take up to 2 min for all vehicle systems to power down.
  2. Test for less than 10 Ω between the Q2 A/C Compressor Clutch ground circuit terminal 1 and ground.
    • If 10 Ω or greater 
    1. Ignition OFF.
    2. Test for less than 2 Ω in the ground circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, repair the open/high resistance in the ground connection.
    • Go to next step: If less than 10 Ω 
  3. Connect a test lamp between the control circuit terminal 2 and ground, ignition ON.
  4. Verify the test lamp does not turn ON and OFF when commanding the Q2 A/C Compressor Clutch On and Off with a scan tool.
    • If the test lamp turns ON and OFF 

      Test or replace the Q2 A/C Compressor Clutch.

    • Go to next step: If the test lamp does not turn ON and OFF 
  5. Ignition OFF, remove the test lamp and connect the harness connector at the Q2 A/C Compressor Clutch. Disconnect the X3 harness connector at the X50A Fuse Block - Underhood, ignition ON.
  6. Verify the Q2 A/C Compressor Clutch is not activated.
    • If the Q2 A/C Compressor Clutch is activated 
    1. Ignition OFF, disconnect the harness connector at the Q2 A/C Compressor Clutch, ignition ON.
    2. Test for less than 1 V between the control circuit terminal 2 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, test or replace the Q2 A/C Compressor Clutch.
    • Go to next step: If the Q2 A/C Compressor Clutch is not activated 
  7. Connect a 10 A fused jumper wire between the control circuit terminal 50 and B+.
  8. Verify the Q2 A/C Compressor Clutch activates.
    • If the Q2 A/C Compressor Clutch does not activate 
    1. Ignition OFF, remove the jumper wire, disconnect the harness connector at the Q2 A/C Compressor Clutch, ignition ON.
    2. Test for infinite resistance between the control circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 Ω in the control circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, test or replace the Q2 A/C Compressor Clutch.
    • Go to next step: If the Q2 A/C Compressor Clutch activates 
  9. Ignition OFF, connect the X3 harness connector at the X50A Fuse Block - Underhood and disconnect the harness connector at the K20 Engine Control Module, ignition ON.
  10. Verify the Q2 A/C Compressor Clutch is not activated.
    • If the Q2 A/C Compressor Clutch is activated 
    1. Ignition OFF, disconnect the X3 harness connector at the X50A Fuse Block - Underhood.
    2. Test for infinite resistance between the X3 X50A Fuse Block - Underhood control circuit terminal 34 and ground.
      • If less than Infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, test or replace the X50A Fuse Block - Underhood.
    • Go to next step: If the Q2 A/C Compressor Clutch is not activated 
  11. Connect a 3 A fused jumper wire between the K20 Engine Control Module control circuit terminal for the KR29 A/C Compressor Clutch Relay and ground.
  12. Verify the Q2 A/C Compressor Clutch activates.
    • If the Q2 A/C Compressor Clutch does not activate 
    1. Ignition OFF, remove the jumper wire, disconnect the X3 harness connector at the X50A Fuse Block - Underhood, ignition ON.
    2. Test for less than 1 V between the X3 X50A Fuse Block - Underhood control circuit terminal 34 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the control circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, test or replace the X50A Fuse Block - Underhood.
    • Go to next step: If the Q2 A/C Compressor Clutch activates 
  13. Replace the K20 Engine Control Module.
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