Network, generic

U0051 Vehicle Communication Bus C (-) Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

(-) wire of Bus C broken at a flex point or splice
Terminal pushed back or spread in a Bus C connector
Corroded splice interrupting the (-) line

Symptoms

  • Modules beyond the break no longer respond
  • Code comes and goes while other modules keep working

Repair estimate

DifficultyHardWorkshop job
Parts and labour€60–700
Time0.5–5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

bus c wiringmodule connector

Related codes

U0042U0046U0048U0052U0054

References: nxp.com, nxp.com, serdia.deutz.com, law.cornell.edu.