P0645 - OBD Trouble Code

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P0645 is a diagnostic trouble code (DTC) for "A/C Clutch Relay Control Circuit". This code indicates that a fault has been detected in the A/C clutch relay control circuit. The PCM or one of the other supporting control modules has detected this fault. Due to this code the A/C of your vehicle may not function properly or may not work at all and check engine light will illuminate.

The P0645 OBD-II trouble code is associated with the air conditioning (A/C) clutch relay control circuit. This is a generic diagnostic trouble code (DTC) and applies to many OBD-II vehicles. The purpose of the A/C clutch relay control circuit is to control the operation of the air conditioning. This is accomplished by providing power to the A/C clutch to engage the A/C compressor. This code can be identified by the PCM or other supporting modules and this code will be detecting when there are improper signals within the A/C clutch relay control electrical circuit.

In the event of an a/c clutch relay control circuit fault, a trouble code will be stored and a service engine soon lamp will be illuminated.

What causes this problem with the A/C Clutch Relay Control Circuit?

• Faulty A/C Clutch
• Inoperative A/C Clutch relay
• Defective control module ground strap
• Flawed or faulty wiring
• Blown fuses
• Fallacious connector
• Inoperative A/C

1. A/C Clutch Relay - The air conditioning clutch relay transfers power, like a switch, from the interior A/C controls of an automobile to the A/C compressor, engaging the compressor clutch. Replace or repair it if you discover it faulty.
2. A/C Compressor - The compressor is the power unit of the air-conditioning system that puts the refrigerant under high pressure before it pumps it into the condenser, where it changes from a gas to a liquid. It should be inspected thoroughly and repaired as required.
3. A/C Clutch - The A/C Clutch is an electromagnetic device that engages and disengages the AC compressor pulley from the compressor drive. The AC compressor is a pump that is driven by the engine crankshaft through a belt pulley. However, the compressor needs to run only when the air conditioner is turned on. Check out the A/C Clutch thoroughly and if you find it faulty replace it.

The symptoms of this code are might not noticeable except flashing of check engine light, apart from this other symptom may include:

• A/C functioning badly
• A/C may not work at all

The main problem you will face due to this code is inconvenience without A/C. If you prefer to drive in comfort, and you’re A/C isn’t working properly then you needed to fix this code on priority. However, people who can manage without A/C can fix this code as per their convenience. As this code is not serious but keeping a trouble code for a long is not a good idea. Following repairs or replacements may help you to fix this code:

• Replacing the A/C clutch relay
• Replacing blown fuse or fuse-able link (if applicable)
• Cleaning corrosion from connectors
• Evacuate and recharge A/C system
• Repairing or replacing wiring
• Repairing or replacing ground straps
• Replacing a control module
• Replacing the A/C clutch
• Replacing the A/C Compressor
• Flashing or replacing PCM

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Here are some steps which you should follow in order to diagnose this fault code:

• Visually inspect to check the associated wiring for obvious defects such as scraping, rubbing, bare wires, or burn spots.
• Check the connectors and connections for security, corrosion and damaged pins.
• All wiring connectors and connections to components including control modules and ground straps should be checked thoroughly and repair or replace as necessary.
• Re-test the system to determine if the repairs have been effective.
• Clear out the codes and see if they return when the vehicle is operating.
• Test drives the vehicle.

Common Mistakes When Diagnosing the P0645 Code

Symptoms and stored codes that are present as a reaction to a communication failure are often misdiagnosed and repaired as the cause of the problem. Obviously, this leads to an unsuccessful repair.