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

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

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

B+

P0646

P0647

P0647

--

Control

P0646

P0647

P0647

--

Circuit/System Description

The engine control module (ECM) controls the A/C compressor clutch based on an A/C request message from the HVAC control module. The ECM monitors the A/C refrigerant pressure sensor and if pressure is within a specified range, will engage the A/C compressor by grounding the A/C compressor clutch relay control circuit.

B+ is applied to the A/C relay in the RUN/START position and with the A/C compressor clutch relay control circuit grounded by the ECM, current flows through the coil side of the A/C relay. With current flowing through the coil side of the relay, a magnetic field is created which pulls the switch side of the relay closed, sending current to the A/C compressor clutch, allowing the A/C compressor to be engaged.

Conditions for Running the DTC

P0646 (Without FX3)

    • The engine is running.
    • The DTC runs continuously when the above conditions are met.

P0647 (Without FX3)

    • The engine is running.
    • The A/C relay is commanded ON.
    • The DTC runs continuously when the above conditions are met.

P0646 or P0647 (FX3)

    • DTC P0562 or P0563 is not set.
    • The engine is running.
    • The ignition voltage is between 11-16V.
    • The DTC runs continuously when the above conditions are met.

Conditions for Setting the DTC

P0646

The ECM detects a short circuit to ground or an open/high resistance on the A/C clutch relay control circuit.

P0647

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

Action Taken When the DTC Sets

DTC P0646 and P0647 are Type C DTCs.

Conditions for Clearing the DTC

DTC P0646 and P0647 are Type C DTCs.

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Manual HVAC Description and Operation

Electrical Information Reference

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

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information.

Circuit/System Verification

Engine running, command the A/C Relay On and OFF with a scan tool. The Q2 A/C Compressor Clutch should engage and disengage.

Circuit/System Testing

  1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay.
  2. Ignition ON, verify a test lamp illuminates between the relay coil B+ circuit terminal 85 and ground.
  3. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  4. Ignition OFF, connect a test lamp between the relay coil B+ circuit terminal 85 and the relay control circuit terminal 86.
  5. Ignition ON, command the A/C relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
  6. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the K20 ECM.
    If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K20 ECM.
  7. If all circuits test normal, test or replace the KR29 A/C Compressor Clutch Relay.

Component Testing

  1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay.
  2. Test for 70--110 Ω of resistance between terminals 85 and 86.
  3. If not within the specified range, replace the KR29 A/C Compressor Clutch Relay.
  4. Test for infinite resistance between the following terminals:
  5. • 30 and 86
    • 30 and 87
    • 30 and 85
    • 85 and 87
    If not within the specified range, replace the KR29 A/C Compressor Clutch Relay.
  6. Install a 20A fused jumper wire between terminal 85 and B+. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 Ω between terminal 30 and 87.
  7. If greater than the specified range, replace the KR29 A/C Compressor Clutch Relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for ECM replacement, setup, and programming.

   


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