OBD-II code · Network
U0039 Vehicle Communication Bus B (+) Open
Bus B high-side line is open — broken wire or disconnected. 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 U0039?
The car may go into limp mode (reduced power). Get it diagnosed before a long trip.
Common causes
- Most likelyWire broken or connector unplugged
- 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
- 1–5 h
- Emissions test
- Usually unaffected
- Parts involved
- Bus B Wiring
Related codes
- U0031Vehicle Communication Bus C (+) 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
- U0078Vehicle Communication Bus B (+) Open
- U008BVehicle Communication Bus G (+) Open
- U0094Vehicle Communication Bus H (+) Open
- U0036Vehicle Communication Bus A (-) shorted to Bus A (+)
- U0037Vehicle Communication Bus B
- U0038Vehicle Communication Bus B Performance
- U0040Communication Bus Off
- U0041Vehicle Communication Bus B (+) High
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.