Trouble code solution P0645: decoding, causes, resetting, meaning

Contents

Technical description and explained code P0645
Symptoms of vehicle malfunctions
Factors that can cause this error code
How to fix or reset OBD-2 code P0645
Diagnose and repair of problems
Checking voltage
On which vehicles does this problem occur most frequently
Video

Fault code P0645 is called “A/C Clutch Relay Control Circuit Malfunction” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0645

If your OBD-II equipped vehicle has stored code P0645. This means that the transmission control module (PCM) has detected a fault. Which is related to the air conditioner clutch (A/C) relay control circuit.

The air conditioner clutch relay control circuit is designed to control the operation of the air conditioner. The operation is done by supplying power to the air conditioner clutch, and then the air conditioner compressor is turned on.

Depending on the specific vehicle, this circuit can be very complex and include several control modules.

When the transmission control module (PCM) or one of the other supporting control modules detects incorrect signals. That go through the electrical circuit controlling the air conditioner clutch relay, code P0645 is set.

Depending on the vehicle and the specific fault, this code may be detected up to eight times before the check engine light comes on. Code P0645 is then set by the PCM. This means that the control module detects a general fault in the air conditioner relay control circuit.

Symptoms of vehicle malfunctions

The main signal that an error P0645 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

The “Check engine” control lamp on the control panel will light up (the code will be stored in the memory as a malfunction).
When this error occurs, the vehicle’s air conditioner may not work properly or not effectively.
The air conditioner may not work at all.

The degree of severity of fault code P0645 can vary from insignificant, just burning engine control light while air conditioner is working properly. But the air conditioner may also malfunction or not work at all.

Factors that can cause this error code

The error code P0645 can mean that one or more of the following problems have occurred:

Faulty air conditioner clutch or clutch relay.
Broken control module ground plate.
Open or short circuit in CAN circuit.
Fuse or jumper blown.
Damaged, corroded wiring or connectors.
Low pressure in air conditioning system due to lack of refrigerant.
Faulty PCM or other control module, also possible programming error.

How to fix or reset OBD-2 code P0645

Some suggested steps for troubleshooting and fix the error code P0645:

Inspect the wiring for damage, abrasions, breaks, and shorts. If wiring is damaged, repair or replace it.
Remove all diagnostic trouble codes from the PCM and test drive to see if diagnostic trouble code P0645 returns.
If the problem persists, check the CAN bus pins as well as the related electrical components with a dedicated diagnostic scanner.
Diagnose and, if necessary, replace the air conditioner compressor clutch or clutch relay.
The air conditioner compressor should also be diagnosed.
If everything is OK, the PCM may need to be replaced and reprogrammed.

Diagnose and repair of problems

To rule out all variants of error P0645, visually inspect the wiring and check the battery voltage. Also check the battery terminals and cables for loose connections.

Ensure that the system voltage is as specified in the manual. The charging system is fully operational, and the battery is in good condition.

Checking voltage

The process of checking voltage, no power source or grounding, may require a circuit continuity check. This is done to check the integrity of the wiring, control modules, and other components.

All control module ground cables may need to be included in this process. A continuity check should always be performed with the power off. Normal readings for wiring and connections should be 0 ohms of resistance unless otherwise specified in the specifications.

Resistance or no continuity indicates faulty wiring that is open or shorted and requires repair or replacement. The most common and common error in diagnosing code P0645 is to misdiagnose symptoms and codes.