U0629 code meaning
Lost Communication With A/C Refrigerant Temperature Sensor B
What U0629 means
A second refrigerant temperature point is typical where an electronic expansion valve meters flow, for instance at the evaporator or chiller outlet, so that superheat can be calculated from temperature and pressure. U0629 is logged when the controller stops getting answers from temperature sensor B over its serial link. A digital sensor can diagnose its own measuring element, so U0629 points to the transmission path or to a sensor that has gone completely silent, not to a merely implausible reading. When U0628 is stored as well, a combined pressure/temperature unit B or its line is the likely common cause. No manufacturer documents U0629 publicly. Often only one operating mode, such as battery chilling or heat pump, is lost. Analog circuit faults are P0EC1 to P0EC4.
U0629 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0629
- Battery cooling or heat-pump mode unavailable
- Uneven or reduced A/C performance
Common causes of U0629
- Most likelyLIN line or connector at temperature sensor B open, shorted or corroded
- PossibleCombined pressure/temperature unit B failed (often together with U0628)
- Less likelyFuse or supply feed for sensor B open
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Ac refrigerant temp sensor bVehicle bus wiring
What each part of U0629 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 29 | The exact fault in that area. |
What to do next
- Note U0629 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0629
What does U0629 mean?
U0629 means "Lost Communication With A/C Refrigerant Temperature Sensor B". A second refrigerant temperature point is typical where an electronic expansion valve meters flow, for instance at the evaporator or chiller outlet, so that superheat can be calculated from temperature and pressure. It is a generic code, so it means the same on every make.
Is it safe to drive with U0629?
U0629 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U0629 fail an emissions test?
U0629 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0629 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. This is a job for a workshop.
Will U0629 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.