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U0628 — Lost Communication Ac Refrigerant Pressure Sensor B

Generic OBD-II · all makesNetwork / communication

The vehicle detects that it is no longer receiving data from the secondary A/C refrigerant pressure sensor on the CAN network.

Symptoms

What causes it — most likely first

1. Faulty A/C refrigerant pressure sensor B

The sensor itself can fail or provide out‑of‑range signals, causing the PCM to lose communication.

2. Damaged wiring or poor connector at sensor B

Open circuits, corrosion, or pin damage can interrupt the sensor’s signal on the CAN bus.

3. CAN bus network issue affecting sensor B

A break, termination fault, or high‑resistance condition elsewhere on the network can prevent the sensor’s messages from reaching the PCM.

4. Powertrain control module communication fault

A rare internal failure in the PCM’s CAN interface may cause loss of data from the sensor.

How it's diagnosed

  1. Verify that the A/C system is functioning and note any cooling performance issues.
  2. Use a scan tool to read live data for sensor B and check for valid voltage or resistance values.
  3. Inspect the sensor’s wiring harness and connector for corrosion, damage, or loose pins.
  4. Perform a CAN bus continuity test to identify any open or short circuits on the network.
  5. If wiring and sensor appear sound, test the PCM’s CAN module for proper operation or replace the PCM as a last resort.

Code facts & related codes

SystemNetwork / communication
StandardizationSAE generic — identical on every make
Related codesU0620 — Lost Communication Exhaust Gas TemperaU0621 — Lost Communication Exhaust Gas TemperaU0622 — Lost Communication Exhaust Gas TemperaU0623 — Lost Communication Coolant PumpU0624 — Lost Communication Coolant Pump BU0625 — Lost Communication Fuel Rail Pressure

Frequently asked

Can I just replace the PCM to fix U0628?

Replacing the PCM is seldom necessary; the issue is usually a bad sensor, wiring problem, or CAN network fault.

Will the code clear itself if the A/C is turned off?

No, the code persists until the underlying communication fault is resolved, even if the A/C system is not in use.

Is this code related to refrigerant pressure in the system?

The code indicates a loss of communication with the sensor that measures pressure; it does not directly indicate low or high refrigerant pressure.

Can a blown fuse cause this code?

Yes, if the fuse supplying power to the sensor circuit is blown, the sensor will not transmit data, triggering U0628.