U0629: Lost Communication With A/C Refrigerant Temperature Sensor B

What it means

A control module has stopped receiving expected network messages from A/C refrigerant temperature sensor B. The effect on A/C operation depends on the vehicle's system design.

How it works

A/C refrigerant temperature sensor B reports temperature over the vehicle network for A/C control. The receiving module monitors for sensor B's expected messages, and U0629 sets when those messages are lost. The system may limit A/C operation without that temperature input.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

Symptoms

• A/C may not operate as intended
• Warning light or message related to the A/C system

How to diagnose it

1. Scan all modules and save event data to see whether sensor B communication loss occurred alongside other network faults.
2. Check A/C live data for refrigerant temperature sensor B and compare with sensor A if both readings are available.
3. Inspect sensor B's connector and nearby bus wiring for loose pins, corrosion, chafing, or moisture.
4. Check the sensor module's power and ground against the manufacturer's specification.
5. Test the network wiring serving temperature sensor B for opens or shorts using the vehicle wiring diagram and manufacturer's procedure.

Common fixes

• Clean and secure sensor B's connector or repair damaged wiring.
• Restore the sensor module's power or ground.
• Repair an open or short in the communication bus to temperature sensor B.
• Replace the sensor module after confirming the wiring and its power and ground are sound.

Can I keep driving?

Driving is generally unaffected, but cooling or demisting may be reduced if the A/C system disables itself. Keep the windows clear by another safe method when necessary.