OBD-II code · Network
U0634 Lost Communication With Hybrid/EV Battery Pack Coolant Temperature Sensor A
The vehicle bus reports loss of communication with smart HV battery pack coolant temperature sensor A. Battery cooling and charge/discharge limits switch to a substitute value.
Is it safe to drive with U0634?
The car may go into limp mode (reduced power). Get it diagnosed before a long trip.
Common causes
- Most likelyBus wiring open or shorted
- PossibleModule without power or ground
- PossibleModule failed
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.5–3 h
- Emissions test
- Usually unaffected
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Hv Battery Coolant Temp Sensor A, Vehicle Bus Wiring
Related codes
- U0635Lost Communication With Hybrid/EV Battery Pack Coolant Temperature Sensor B
- U0631Lost Communication With Engine Coolant Temperature Sensor 5
- U0632Lost Communication With Fan 1
- U0633Lost Communication With Fan 2
- U0636Lost Communication With Hybrid/EV Battery Pack Coolant Control Valve A
- U0637Lost Communication With Hybrid/EV Battery Pack Coolant Control Valve B
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.