OBD-II code · Network
U0078 Vehicle Communication Bus B (+) Open
The plus wire of bus B is open. Modules on this segment lose communication. 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 U0078?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyBus-B plus wire broken
- 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
- 0.8–4 h
- Emissions test
- Usually unaffected
- Parts involved
- Can High Wire
Related codes
- U0031Vehicle Communication Bus C (+) Open
- U0039Vehicle Communication Bus B (+) Open
- U0042Vehicle Communication Bus D (+) Open
- U0048Vehicle Communication Bus C (+) Open
- U0050Vehicle Communication Bus E (+) Open
- U0057Vehicle Communication Bus D (+) Open
- U0060Vehicle Communication Bus F (+) Open
- U0066Vehicle Communication Bus E (+) Open
- U008BVehicle Communication Bus G (+) Open
- U0094Vehicle Communication Bus H (+) Open
- U0075Control Module Communication Bus "B" Performance
- U0076Control Module Communication Bus "C" Off
- U0077Vehicle Communication Bus B Off
- U0079Vehicle Communication Bus B (+) Low
- U007AControl Module Communication Bus H Off
- U007BControl Module Communication Bus I Off
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.