OBD-II code · Network
U0091 CAN Communication Bus "C" Off
Bus C (third CAN bus, often used for chassis or infotainment) has entered the bus-off state. All modules on Bus C lose communication.
Is it safe to drive with U0091?
The car may go into limp mode (reduced power). Get it diagnosed before a long trip.
Common causes
- Most likelyBus C shorted to supply or ground
- PossibleBus C terminating resistor failed
- Less likelyGateway module routing CAN messages incorrectly
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
- Can Bus Wiring, Can Terminating Resistor
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.