Network, generic

U0033 Vehicle Communication Bus A (-) Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U0033 reports an interruption of the (-) wire of Vehicle Communication Bus A; on a dual-line CAN like the sensor/hybrid CAN Audi lists as Bus A, that is CAN-Low. As with U0030, the network falls apart into pieces that can no longer hear each other, and NXP stresses that a standard high-speed transceiver has no means of detecting an open wire on its own. The control module infers the fault indirectly, for example from expected messages that stop arriving or from rising error counters, so the code often appears next to lost-communication entries for modules beyond the break. No manufacturer documents U0033 publicly. With the battery disconnected, a resistance between (+) and (-) that differs from the normal termination value hints at the break; check recently separated connectors first.

Likely causes

(-) wire of Bus A broken in the harness
Pushed-back or corroded terminal in a connector
Connector not reconnected after a repair

Symptoms

  • Modules beyond the break stop responding
  • 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 a wiringbus a terminatormodule connector

Related codes

U0006U0028U0030U0034U0035

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