OBD-II code · Network
U0034 Vehicle Communication Bus A (-) Low
Bus A low-side line voltage below the expected range. Short to ground or transceiver pulling line low.
Is it safe to drive with U0034?
The car may go into limp mode (reduced power). Get it diagnosed before a long trip.
Common causes
- Most likelyCAN-L shorted to ground
- Less likelyGateway module routing CAN messages incorrectly
- Less likelyCAN terminating resistor (120 Ω) drifted out of spec
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
- Hard
- DIY friendly
- Best left to a mechanic
- Typical labour
- 1–6 h
- Emissions test
- Usually unaffected
- Parts involved
- Bus A Wiring, Bus A Transceiver
Related codes
- U0043Vehicle Communication Bus B (-) Low
- U0052Vehicle Communication Bus C (-) Low
- U0061Vehicle Communication Bus D (-) Low
- U008FVehicle Communication Bus G (-) Low
- U0098Vehicle Communication Bus H (-) Low
- U0031Vehicle Communication Bus C (+) Open
- U0032Vehicle Communication Bus A (+) High
- U0033Vehicle Communication Bus A (-) Open
- U0035Vehicle Communication Bus A (-) High
- U0036Vehicle Communication Bus A (-) shorted to Bus A (+)
- U0037Vehicle Communication Bus B
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.