U0042Vehicle Communication Bus B (-) Open
- Generic OBD-II code · Network
- How the car detects it
- 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.
- What you may notice
- Modules beyond the break no longer respond
- Lost-communication codes stored alongside
- Likely causes
- Likely(-) wire of Bus B broken in the harness
- PossibleCorroded or pushed-back terminal in a connector
- PossibleConnector not reconnected after a repair
- Repair
- Hard · Usually a job for a workshop.Typical cost: €60 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.