Network, generic

U0042 Vehicle Communication Bus B (-) Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U0042 points to an interrupted (-) wire on Vehicle Communication Bus B; on a CAN-type bus that is CAN-Low. The network then splits along the break, and on a standard high-speed CAN neither side's transceiver can tell what happened, since NXP states that line interruptions escape even transceiver diagnosis. Detection rests on time-outs for messages from nodes on the far side. On a fault-tolerant low-speed CAN, the TJA1055 data sheet from NXP treats a CAN-Low interruption as a failure that frames in progress survive. A resistance check across the two bus wires at a central connector helps: with both terminations reachable it reads about 60 ohms, a break in one wire leaves only the near terminator at about 120 ohms. No manufacturer documents U0042 publicly; start with connectors that were opened recently.

Likely causes

(-) wire of Bus B broken in the harness
Corroded or pushed-back terminal in a connector
Connector not reconnected after a repair

Symptoms

  • Modules beyond the break no longer respond
  • Lost-communication codes stored alongside

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 b wiringmodule connector

Related codes

U0033U0037U0039U0043U0044

References: nxp.com, nxp.com, onsemi.com.