P0645 - A / C CLUTCH RELAY CONTROL CIRCUIT

The A/C clutch relay control circuit monitors the operation of the air conditioner. To do this, power is supplied to the A/C clutch to connect the A/C compressor. This circuit can be very complex, and it includes several modules, depending on the vehicle manufacturer.

The PCM (Powertrain Control Module) sets the DTC P0645 OBDII and activates the Check Engine light when a general malfunction is detected in the air conditioning relay control circuit.

• Engine malfunction light ON.
• A/C malfunction light.
• If you drive during hot weather, the air conditioner operates wrongly.

The P0645 OBD2 error code setting occurs when:

• The A / C clutch relay may be faulty.
• The A/C clutch may be in bad condition.
• Wires in the CAN (Control Area Network) bus harness may be corroded or causing a short.
• The ground wire may have defects.

Steps to solve the P0645 OBDII diagnostic code :

• Check for Technical Service Bulletins (TSB).
• Thoroughly inspect all the associated cables. If you find some defects such as burns or corrosion, repair or replace them. Due to the complexity of the system, it is composed of many relays and fuses in some models. Make sure to check them all.
• Test for continuity to verify the integrity of the wiring, the modules involved, and other components. Check all the ground wires. Normal readings for connections should be 0 ohms resistance unless specifications show otherwise. Lack of continuity is because of a shortage in the system, fix or replace.
• Change the A / C clutch relay.