OBD-II code · Network
U0038 Vehicle Communication Bus B Performance
Bus B is electrically OK but message rate or error counters are outside spec. Often intermittent wiring or a degraded transceiver.
Is it safe to drive with U0038?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyWiring chafed or marginal
- 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
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Bus B Wiring
Related codes
- U0047Vehicle Communication Bus C Performance
- U0056Vehicle Communication Bus D Performance
- U0065Vehicle Communication Bus E Performance
- U0081Vehicle Communication Bus F Performance
- U008AVehicle Communication Bus G Performance
- U0093Vehicle Communication Bus H Performance
- U009CVehicle Communication Bus I Performance
- U009EVehicle Communication Bus J Performance
- U0035Vehicle Communication Bus A (-) High
- U0036Vehicle Communication Bus A (-) shorted to Bus A (+)
- U0037Vehicle Communication Bus B
- U0039Vehicle Communication Bus B (+) Open
- U0040Communication Bus Off
- U0041Vehicle Communication Bus B (+) High
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.