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DTC P0645, P0646, or P0647

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    • Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0645: Air Conditioning (A/C) Compressor Clutch Relay Control Circuit

DTC P0646: Air Conditioning (A/C) Compressor Clutch Relay Control Circuit Low Voltage

DTC P0647: Air Conditioning (A/C) Compressor Clutch Relay Control Circuit High Voltage

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

A/C Compressor Clutch Relay Coil Ignition

P0646

P0645, P0646

--

--

A/C Compressor Clutch Relay Coil Control

P0646

P0645, P0646

P0647

1

1. A/C Compressor Malfunction

Circuit/System Description

When the A/C switch is pressed, the HVAC control module sends an A/C request message to the engine control module (ECM) via CAN-Bus. Therefore, the ECM grounds the A/C compressor clutch relay control circuit, which will switch the A/C compressor clutch relay. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch. The A/C compressor clutch will be activated.

Conditions for Running the DTC
    • Engine is running.
    • The HVAC control module is ON.
    • The A/C switch is active.

Conditions for Setting the DTC

P0645 or P0646

The ECM detects a short to ground or an open at the A/C compressor clutch relay control circuit.

P0647

The ECM detects a short to voltage at the A/C compressor clutch relay control circuit.

Action Taken When the DTC Sets

P0645 or P0646

The A/C compressor is inoperative or always active.

P0647

The A/C compressor is inoperative.

Conditions for Clearing the DTC

The condition for setting the DTC is no longer present.

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification
  1. Ignition ON.
  2. Verify the A/C Compressor Clutch Relay clicks when commanding the A/C clutch ON and OFF with a scan tool.
    3. [ARW-LISTFAIL]

  3. If the relay does not click

    Refer to Circuit/System Testing

    4. [/ARW-LISTFAIL][ARW-LISTPASS]

  4. If the relay clicks

    5. [/ARW-LISTPASS]
  5. All OK.

Circuit/System Testing

  1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay, ignition ON.
  2. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
    3. [ARW-LISTFAIL]

  3. If the test lamp does not illuminate and the circuit fuse is good

    4. [/ARW-LISTFAIL]
    2.1. Ignition OFF.
    2.2. Test for less than 2 Ω in the B+ circuit end to end.
    [ARW-LISTFAIL]

  4. If 2 Ω or greater, repair the open/high resistance in the circuit.

  5. If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

    6. [/ARW-LISTFAIL] [ARW-LISTFAIL]

  6. If the test lamp does not illuminate and the circuit fuse is open

    7. [/ARW-LISTFAIL]
    2.1. Ignition OFF.
    2.2. Test for infinite resistance between the B+ circuit and ground.
    [ARW-LISTFAIL]

  7. If less than infinite resistance, repair the short to ground on the circuit.

    8. [/ARW-LISTFAIL][ARW-LISTPASS]

  8. If infinite resistance

    9. [/ARW-LISTPASS]
    2.3. Test for greater than 1 Ω between the control circuit terminal 85 and ground.
    [ARW-LISTFAIL]

  9. If less than 1 Ω, repair the short to ground on the circuit.

    10. [/ARW-LISTFAIL][ARW-LISTFAIL]

  10. If greater than 1 Ω, test or replace the KR29 A/C Compressor Clutch Relay

    11. [/ARW-LISTFAIL] [ARW-LISTPASS]

  11. If the test lamp illuminates

    12. [/ARW-LISTPASS]
  12. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
  13. Verify the test lamp turns ON and OFF when commanding the Q2 A/C Compressor Clutch ON and OFF with a scan tool.
    14. [ARW-LISTFAIL]

  14. If the test lamp is always OFF

    15. [/ARW-LISTFAIL]
    4.1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
    4.2. Test for less than 1 V between the control circuit and ground.
    [ARW-LISTFAIL]

  15. If 1 V or greater, repair the short to voltage on the circuit.

    16. [/ARW-LISTFAIL][ARW-LISTPASS]

  16. If less than 1 V

    17. [/ARW-LISTPASS]
    4.3. Ignition OFF.
    4.4. Test for less than 2 Ω in the control circuit end to end.
    [ARW-LISTFAIL]

  17. If 2 Ω or greater, repair the open/high resistance in the circuit.

    18. [/ARW-LISTFAIL][ARW-LISTFAIL]

  18. If less than 2 Ω, replace the K20 Engine Control Module.

    19. [/ARW-LISTFAIL] [ARW-LISTFAIL]

  19. If the test lamp is always ON

    20. [/ARW-LISTFAIL]
    4.1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
    4.2. Test for infinite resistance between the control circuit and ground.
    [ARW-LISTFAIL]

  20. If less than infinite resistance, repair the short to ground on the circuit.

    21. [/ARW-LISTFAIL][ARW-LISTFAIL]

  21. If infinite resistance, replace the K20 Engine Control Module.

    22. [/ARW-LISTFAIL] [ARW-LISTPASS]

  22. If the test lamp turns ON and OFF

    23. [/ARW-LISTPASS]
  23. Test or replace the KR29 A/C Compressor Clutch Relay and verify the DTC does not reset. If the DTC resets, replace the K20 Engine Control Module.

Component Testing

Static Test

  1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay.
  2. Test for 60-180 Ω between the B+ terminal 85 and the control terminal 86 of the KR29 A/C Compressor Clutch Relay.
    3. [ARW-LISTFAIL]

  3. If not within the specified range, replace the KR29 A/C Compressor Clutch Relay.

    4. [/ARW-LISTFAIL]

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for engine control module replacement, setup, and programming

   


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