how to fix p0645 fault code

The P0645 code signifies a diagnostic trouble code (DTC) for the “A/C Clutch Relay Control Circuit.” This DTC alerts you that a problem has been identified in the A/C clutch relay control circuit of your vehicle. The PCM or one of the other supporting control modules has detected this issue. As a result of this code, your vehicle’s A/C may experience improper functioning or may fail altogether, leading to the illumination of the check engine light.


P0645 A/C Clutch Relay Control Circuit

p0645 code

If your vehicle’s PCM has logged a P0645 code, it indicates that there’s an issue within the A/C clutch relay control circuit.



What the P0645 code means

OBD-II Code P0645 signifies an issue with the A/C clutch relay control circuit. In vehicles equipped with an engine control module (PCM), this circuit is responsible for regulating voltage to the A/C compressor clutch. The clutch engagement enables the operation of the vehicle’s air conditioning system. When the PCM encounters difficulty controlling the relay associated with this circuit, it triggers the setting of code P0645.


  • A/C not working well or not working at all.
  • Check if the engine light illuminates.

Common Causes:

  • Faulty A/C clutch relay.
  • Defective air conditioning clutch.
  • Broken ground plate on the control module.
  • Defective control module.
  • Blown fuse or jumper wire (if applicable).
  • a corroded or damaged connector.
  • Low or overly maintained air conditioning system.
  • Faulty or damaged wiring.
  • Faulty A/C compressor.
  • Defective PCM.

Troubleshooting Steps:

  • Review vehicle-specific Technical Service Bulletins (TSBs).
  • ConductConduct a thorough visual inspection of the associated wiring for defects.
  • Check connectors and connections for security, corrosion, and damage.
  • Perform advanced troubleshooting using a digital multimeter and technical reference documents.
    • Conduct a voltage test.
    • Perform continuity tests to verify the integrity of the wiring and components.

Standard Fixes:

  • Replace the A/C clutch relay.
  • Replace the blown fuse or fuse (if applicable).
  • Clean connectors from corrosion.
  • Evacuate and prime the air conditioning system.
  • Repair or replace the wiring.
  • Repair or replace grounding tapes.
  • Replace the control module.
  • Replace the A/C compressor.
  • Flash or replace PCM.

Common Mistakes:

  • Misdiagnosing symptoms and codes is due to the complexity of the issue.
  • Replacing A/C components without addressing damaged wiring or components.

How do I fix the DTC P0645?

Examine the ‘Possible Causes’ outlined above meticulously. Conduct a visual inspection of the relevant wiring harness and connectors. Scrutinize for any signs of damage, including broken, bent, pushed-out, or corroded connector pins.

The severity of this code can vary, ranging from a mere warning light on the engine when the air conditioner is functioning correctly to experiencing poor or no performance.

Identify and rectify the common issues that typically trigger the P0645 code.

A/C compressor failure
A/C compressor relay failure
Powertrain Control Module (PCM) failure
Wiring issue

Symptoms of a P0645 trouble code may include:

Common SymptomsCommon Causes
The air conditioner does not work wellFaulty A/C clutch relay
The air conditioner does not workDefective air conditioning clutch
Check engine light is onBroken ground plate on control module
Defective control module
Blown fuse or jumper wire (if applicable)
Corroded or damaged connector
Low or overly maintained air conditioning system
Broken ground plate on the control module
Faulty A/C Compressor
Defective PCM

What is the Cost to Diagnose the Code P0645?

Service OfferedDetails
Diagnostic Service Cost$154.99
Diagnosis TimeTypically, 1 hour of labor
Common Causes of the P0645 CodeFaulty A/C compressor, Defective PCM
Symptoms of P0645 CodeMalfunctioning A/C that doesn’t run
Additional CostsTypically, 1.0 hours of labor
Labor RatesTypically between $75 and $150 per hour


The P0645 DTC signals a problem with the A/C clutch relay control circuit, potentially causing air conditioning issues. It’s a common code across OBD-II vehicles, usually detected by the PCM or related modules. Resolving it may involve inspecting and repairing wiring, relays, or control modules.

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