Network, generic

U0030 Vehicle Communication Bus A (+) Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U0030 stands for an open circuit in the (+) wire of Vehicle Communication Bus A. What that wire is depends on the network a maker assigns to Bus A; where it is a two-wire CAN, like the sensor/hybrid CAN Audi files under this name in its 48 V mild hybrids, the (+) line is CAN-High. A break splits the bus: nodes on opposite sides lose each other, while modules sharing an intact section may still exchange frames. NXP points out that ordinary high-speed transceivers cannot recognise an interrupted wire themselves, so the module has to deduce it from missing partners or error counters. No manufacturer documents U0030 publicly; CARB only requires missing communication from digital inputs to be detected and coded separately. Check terminals, splices and the resistance between (+) and (-).

Likely causes

(+) wire of Bus A broken in the harness
Terminal backed out or spread in a connector
Connector left unplugged after a repair

Symptoms

  • Functions served by modules beyond the break stop working
  • Lost-communication codes for some modules on Bus A

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 a wiringmodule connector

Related codes

U0003U0028U0031U0032U0033

References: nxp.com, law.cornell.edu, static.nhtsa.gov.