OBD-II code U0605 indicates that the engine control module (ECM) or another control module has lost communication with the AC refrigerant pressure sensor. This sensor monitors refrigerant pressure and sends data over a vehicle network; a communication failure can disable the air conditioning system to protect the compressor.
The sensor itself may have failed internally, causing it to stop communicating on the data bus. This is the most common cause.
Corrosion, loose terminals, or broken wires in the sensor harness can interrupt the communication signal or power supply.
A blown fuse can cut power to the sensor or the HVAC module, leading to a loss of communication.
If the vehicle uses a separate HVAC module that acts as a gateway for the sensor data, a failure in that module can cause this code.
A short, open, or high resistance in the communication bus wires between the sensor and the receiving module can prevent data exchange.
Rarely, the engine control module may have an internal communication circuit failure. This should be considered only after all other causes are ruled out.
Yes, the vehicle is usually drivable, but the air conditioning will likely not work. Driving without AC is safe, but in hot weather it can be uncomfortable and may cause the engine cooling fans to run differently.
Almost never. The PCM is very rarely the cause of U0605. The problem is usually the refrigerant pressure sensor, its wiring, or a fuse. Replacing the PCM without thorough diagnosis is a common misdiagnosis and an unnecessary expense.
It measures the pressure of the refrigerant in the AC system and sends that data to the control module. The module uses this information to protect the compressor from damage due to low or high pressure and to control cooling fan operation.
The code may go away after a successful repair and several drive cycles, but it is best to clear it with a scan tool after the fix to ensure the system reinitializes communication properly.