U0079: Control Module Communication Bus G Off
What to do
Nothing has broken. One of your car's computers has deliberately stopped talking to a network to protect it — see U0073.
Seven separate networks means a large commercial or converted vehicle — a van, chassis cab, minibus, motorhome or something with specialist equipment. If yours has been converted or had equipment fitted, go back to whoever did that work before a general workshop; the fault is very often where their wiring meets the vehicle's.
Everything else in this group applies, and the order is worth following because it goes cheapest first:
Have the battery and charging tested — a weak battery causes this on a perfectly healthy network (U0076).
Ask how many computers withdrew. One points at its own wiring; several point at the network itself (U0075).
Ask which one it was — the car already knows, and it is where to start looking (U0074).
And do not accept clearing the codes as a repair. Everything will work afterwards and nothing will have changed (U0078).
What this code means
A module has taken itself off communication bus G. See U0073 for what bus off means.
Two numbering notes close this group, and both prevent a fruitless search.
First, the letters here match the buses at U0028 onward. Bus A off is a withdrawal from the network at U0028, bus B off from the one at U0037, and so on — so identifying the network is the same job, done once, from the vehicle's topology. The two families are two views of the same set of networks, and a bus off code alongside an electrical code for the same letter is one fault seen from both ends.
Second, this family runs to G while the Vehicle Communication Bus family stops at F. So bus G has a withdrawal code here and no electrical codes of its own in the decimal numbering — its variants, where they exist, sit in the letter-suffixed layer. A vehicle with seven networks is a commercial or heavily converted one, and U0080's argument about who installed what applies to it in full.
Everything else in this group applies unchanged: check the battery first as at U0076, count how many modules withdrew as at U0075, read which one it was as at U0074, and remember that clearing the code is not a repair, as at U0078.
Likely causes
Start here
- Poor wiring splice in an aftermarket installation · moderate
- Damaged data bus wiring · moderate
- Corroded or loose connector · easy
- Corroded earth connection · moderate
Less common
- Low system voltage · moderate
- Another module holding the bus down · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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