U0051 code meaning
Vehicle Communication Bus C (-) Open
What U0051 means
U0051 stands for a severed (-) conductor on Vehicle Communication Bus C, CAN-Low where Bus C is a CAN. Deutz, which places Bus C on the fourth CAN channel of the EMR L1 engine control unit, does not use this code and books CAN 4 faults only as open circuit (U0048) or short circuit (U0054). A high-speed transceiver cannot see the interruption itself, as NXP points out, so the module only notices that partners on the far side stop acknowledging or sending. NXP's fault-tolerant low-speed TJA1055 instead compares the edge counts on both wires and flags a difference of four pulses; since that works only when the break lies between sender and receiver, its error output tends to toggle. No car maker documents U0051 publicly. Check CAN-Low continuity connector by connector.
U0051 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyHard
- Typical labor0.5 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0051
- Modules beyond the break no longer respond
- Code comes and goes while other modules keep working
Common causes of U0051
- Most likely(-) wire of Bus C broken at a flex point or splice
- PossibleTerminal pushed back or spread in a Bus C connector
- Less likelyCorroded splice interrupting the (-) line
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Bus c wiringModule connector
What each part of U0051 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 51 | The exact fault in that area. |
What to do next
- Note U0051 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0051
What does U0051 mean?
U0051 means "Vehicle Communication Bus C (-) Open". U0051 stands for a severed (-) conductor on Vehicle Communication Bus C, CAN-Low where Bus C is a CAN. It is a generic code, so it means the same on every make.
Is it safe to drive with U0051?
U0051 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U0051 fail an emissions test?
U0051 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0051 to fix?
Difficulty: hard. A typical repair takes 0.5 to 5 hours of work. This is a job for a workshop.
Will U0051 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.