Network, generic

U0043 Vehicle Communication Bus B (-) Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U0043 reports the (-) line of Vehicle Communication Bus B shorted toward ground. Where Bus B is built like a high-speed CAN, that line is CAN-Low, and the fault is sneaky: onsemi measured frames still getting through, with distorted levels and the node drawing about 72 mA instead of 65 mA, because the CANH driver now pushes current through the termination into ground. NXP lists the case among hidden failures. NXP's fault-tolerant TJA1055 transceiver instead detects the short, switches off its CAN-Low driver and carries on single-wire over CAN-High. In both cases the vehicle tends to run normally, with the code logged by one module or showing up only now and then, which sets it apart from U0040, where the bus goes quiet. No manufacturer documents U0043 publicly; near-zero ohms from CAN-Low to ground confirms it.

Likely causes

(-) wire insulation damaged and touching ground
Harness trapped under a panel or bracket
Faulty transceiver pulling the (-) line to ground

Symptoms

  • Vehicle mostly normal, code stored by a single module
  • Occasional communication errors

Repair estimate

DifficultyHardWorkshop job
Parts and labour€60–700
Time1–5 h

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

Parts involved

bus b wiringbus b transceiver

Related codes

U0034U0037U0040U0042U0044

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