OBD-II code · Network
U0099 Vehicle Communication Bus H (-) High
Bus H low-side line voltage above 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 U0099?
The car may go into limp mode (reduced power). Get it diagnosed before a long trip.
Common causes
- Most likelyWire shorted to battery
- 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 H Wiring
Related codes
- U0035Vehicle Communication Bus A (-) High
- U0044Vehicle Communication Bus B (-) High
- U0053Vehicle Communication Bus C (-) High
- U0062Vehicle Communication Bus D (-) High
- U0090Vehicle Communication Bus G (-) High
- U0096Vehicle Communication Bus H (+) High
- U0097Vehicle Communication Bus H (-) Open
- U0098Vehicle Communication Bus H (-) Low
- U009AVehicle Communication Bus H (-) shorted to Bus H (+)
- U009BVehicle Communication Bus I
- U009CVehicle Communication Bus I Performance
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.