U0634Lost Communication With Hybrid/EV Battery Pack Coolant Temperature Sensor A
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- Liquid-cooled traction batteries check how warm the coolant is where it enters or leaves the pack to decide whether to cool or heat. Where that sensor is a digital node rather than a plain thermistor, the battery or thermal controller can detect when its messages stop, and U0634 records exactly that for sensor A. No manufacturer documents this code publicly; GM, for instance, reads its battery coolant sensors as analog thermistors, with P0C42 to P0C46 for their circuit faults. For hybrids CARB requires every electronic input used for battery thermal management to be monitored like any comprehensive component, so a MIL is to be expected there. Without the reading the controller must estimate pack temperature and may reduce charge or drive power.
- What you may notice
- Hybrid or battery warning lamp, on hybrids also the MIL
- Reduced charging power or limited electric performance
- Likely causes
- LikelyData, supply or ground wire to sensor A damaged
- PossibleConnector at the battery coolant line corroded or loose
- PossibleSensor A electronics failed
- RareBattery or thermal management controller fault
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €80 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.