OBD-II code · Network
U0043 Vehicle Communication Bus B (-) Low
Bus B low-side line voltage below expected range. A communication loss with this module breaks any function relying on its data — diagnostic tools may show 'no response' and dependent modules can fall into limp mode.
Is it safe to drive with U0043?
The car may go into limp mode (reduced power). Get it diagnosed before a long trip.
Common causes
- Most likelyWire 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 B Wiring
Related codes
- U0034Vehicle Communication Bus A (-) Low
- U0052Vehicle Communication Bus C (-) Low
- U0061Vehicle Communication Bus D (-) Low
- U008FVehicle Communication Bus G (-) Low
- U0098Vehicle Communication Bus H (-) Low
- U0040Communication Bus Off
- U0041Vehicle Communication Bus B (+) High
- U0042Vehicle Communication Bus D (+) Open
- U0044Vehicle Communication Bus B (-) High
- U0045Vehicle Communication Bus B (-) shorted to Bus B (+)
- U0046Vehicle Communication Bus C
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.