U0629 indicates that the Powertrain Control Module (PCM) has lost communication with Refrigerant Temperature Sensor B, which monitors the temperature of the refrigerant on the low‑side of the A/C system.
Frayed wires, broken connectors, or corrosion at the sensor plug can interrupt the CAN bus signal.
The sensor itself can fail internally, producing no signal or an out‑of‑range voltage.
Vibration or improper installation can cause the connector pins to lose contact.
A poor ground or a blown fuse/relay that supplies sensor power will prevent communication.
Only after ruling out wiring and sensor problems should a PCM internal fault be considered.
It is possible but uncommon. In most cases the problem is wiring, connector, or the sensor itself. PCM replacement should be a last resort after all other checks are completed.
A reset will turn off the warning temporarily, but if the underlying communication loss remains, the code will return and the A/C may still malfunction.
No. The code relates to the temperature sensor’s signal, not the refrigerant charge. Only replace refrigerant if a separate leak or low‑charge condition is diagnosed.
The vehicle will operate, but the A/C system may not provide cooling and the PCM may limit other functions if multiple communication errors occur. Repair is recommended for comfort and to prevent further diagnostic complications.