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Home >> Chevrolet >> 2020 >> Malibu LS >> Repair and Diagnosis >> External Pages >> Different car >> Section 99 (HVAC - 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 Chevrolet Malibu. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition/Vehicle & All vehicle systems - Off
  2. Remove the component:KR29 A/C Compressor Clutch Relay
  3. Ignition - On / Vehicle - In Service Mode
  4. Verify a test lamp turns On between the test points:Ignition circuit terminal 86 & Ground
    • If the test lamp does not turn On and the circuit fuse is OK 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Test for less than 2 ohms between the test points: Ignition circuit terminal 86 & Output terminal @ Fuse
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Verify the fuse is OK and there is voltage at the fuse.
    • If the test lamp does not turn On and the circuit fuse is open 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Test for infinite resistance between the test points:Ignition circuit terminal 86 & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • If infinite resistance - Replace the component:KR29 A/C Compressor Clutch Relay
    • Go to next step: If the test lamp turns On 
  5. Connect a test lamp between the test points:Ignition circuit terminal 86 & Control circuit terminal 85
  6. Perform the scan tool control function:A/C Compressor Clutch Relay - On and Off

    Verify the test lamp turns On and Off.

    • If the test lamp is always Off 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Disconnect the electrical connector:K20 Engine Control Module
    3. Ignition - On / Vehicle - In Service Mode
    4. Test for less than 1 V between the test points: Control circuit terminal 85 @ Relay Socket & Ground
      • If 1 V or greater - Repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    5. Ignition/Vehicle - Off
    6. Test for less than 2 ohms between the test points:Control circuit terminal 85 @ Relay Socket & The other end of the circuit @ Control module harness
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Replace the component:K20 Engine Control Module
    • If the test lamp is always On 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Disconnect the electrical connector:K20 Engine Control Module
    3. Test for infinite resistance between the test points:Control circuit terminal 85 @ Relay Socket & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • If infinite resistance - Replace the component:K20 Engine Control Module
    • Go to next step: If the test lamp turns On and Off 
  7. Verify a test lamp turns On between the test points:B+ circuit terminal 30 & Ground
    • If the test lamp does not turn On and the circuit fuse is OK 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Test for less than 2 ohms between the test points:B+ circuit terminal 30 @ Relay Socket & Output terminal @ Fuse
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Verify the fuse is OK and there is voltage at the fuse.
    • If the test lamp does not turn On and the circuit fuse is open 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Test for infinite resistance between the test points:B+ circuit terminal 30 & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Disconnect the electrical connector:Q2 A/C Compressor Clutch
    4. Test for infinite resistance between the test points:Control circuit terminal 87 @ Relay Socket & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    5. Replace the component:Q2 A/C Compressor ClutchFuse
    6. Install the component:KR29 A/C Compressor Clutch Relay
    7. Connect a test lamp between the test points:Control circuit terminal 2 & Ground circuit terminal 1
    8. Ignition - On / Vehicle - In Service Mode
    9. Perform the scan tool control function:A/C Compressor Clutch Relay - On and Off

      Verify the test lamp turns On and Off.

      • If the test lamp does not turn On and Off - Test or replace the component:KR29 A/C Compressor Clutch Relay
      • If the test lamp turns On and Off - Test or replace the component:Q2 A/C Compressor Clutch
    • Go to next step: If the test lamp turns On 
  8. Momentarily connect a 10 A fused jumper wire between the test points:B+ circuit terminal 30 & Control circuit terminal 87

    Verify the component does not turn On and Off when connecting and disconnecting the jumper wire:Q2 A/C Compressor Clutch

    • If the component turns On and Off 

      Test or replace the component:KR29 A/C Compressor Clutch Relay

    • Go to next step: If the component does not turn On and Off 
  9. Ignition/Vehicle & All vehicle systems - Off
  10. Install the component:KR29 A/C Compressor Clutch Relay
  11. Disconnect the electrical connector:Q2 A/C Compressor Clutch
  12. Test for less than 10 ohms between the test points:Ground circuit terminal 1 & Ground
    • If 10 ohms or greater 
    1. Disconnect the ground connection:Ground
    2. Test for less than 2 ohms between the test points:Ground circuit terminal 1 @ Component harness & The other end of the circuit @ Ground Connection
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Repair the open/high resistance in the ground connection.
    • Go to next step: If less than 10 ohms 
  13. Connect a test lamp between the test points:Control circuit terminal 2 & Ground circuit terminal 1
  14. Ignition - On / Vehicle - In Service Mode
  15. Perform the scan tool control function:A/C Compressor Clutch Relay - On and Off

    Verify the test lamp turns On and Off.

    • If the test lamp is always Off 

      Repair the open/high resistance in the circuit:Control Circuit

    • If the test lamp is always On 

      Repair the short to voltage on the circuit:Control Circuit

    • Go to next step: If the test lamp turns On and Off 
  16. Test or replace the component:Q2 A/C Compressor Clutch
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