Network, generic

U0079 Control Module Communication Bus G Off

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

No manufacturer documents U0079 publicly, so what Bus G is depends entirely on the vehicle. The code belongs to the bus-off family: the controller of the reporting module has collected enough transmit errors to stop sending in order to protect the other nodes. That sets it apart from U0089, the general Bus G fault, and from lost-communication codes such as U0100, which other modules store once they no longer hear the silent one. CARB requires that missing communication of digital inputs and outputs be detected and stored under its own code, which is why a module records its own disconnection. Read all modules first: if only one holds U0079, its transceiver, supply or connector is suspect; if several do, look at the Bus G wiring and termination.

Likely causes

Short between the Bus G wires or to ground
Faulty transceiver in the reporting module
Supply or ground dropouts at the reporting module

Symptoms

  • Functions of the reporting module unavailable
  • Lost-communication codes in other modules

Repair estimate

DifficultyHardWorkshop job
Parts and labour€60–800
Time0.5–5 h

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

Parts involved

bus g wiringcan transceiver

Related codes

U0078U007AU0089U0100

References: law.cornell.edu, onsemi.com, en.wikipedia.org.