What does code U0091 mean?

Q: What does code U0091 mean?

CAN Communication Bus "C" Off. U0091 means the modules on the vehicle's Controller Area Network (CAN) bus 'C' have lost communication with each other, so the computer that set the code can no longer see messages from the other modules on that bus segment. The fault is detected when the module stops receiving the expected periodic CAN frames on bus 'C' for a set period, not necessarily because a wire is broken.

DTC codes / U00xx · Network wiring and bus faults / U0091

U0091CAN Communication Bus "C" Off

U0091 means the modules on the vehicle's Controller Area Network (CAN) bus 'C' have lost communication with each other, so the computer that set the code can no longer see messages from the other modules on that bus segment. The fault is detected when the module stops receiving the expected periodic CAN frames on bus 'C' for a set period, not necessarily because a wire is broken.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaNetwork wiring and bus faults

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.