U0086: Vehicle Communication Bus F (-) Low
What to do
Expect equipment on the converted part of the vehicle to have stopped or to be misbehaving, and probably worse when the equipment is running.
That load-related pattern is the clue, and there is a one-minute test that confirms it.
Ask for the voltage between the vehicle body and the chassis to be measured while the body equipment is running. A good bonding shows a few tens of millivolts. A corroded one shows whole volts — and volts between two parts of a vehicle that should be at exactly the same potential is the fault, stated as plainly as it can be.
That is far simpler and more decisive than tracing network wiring, and it should be the first thing done on a converted vehicle with this code.
The cause is the earth strap between body and chassis — the connection that carries everything the body equipment draws, living under the vehicle in the salt. It is accessible and cheap, which is the best combination there is.
Say whether the problem is worse when the equipment is working, since that is what points here.
What this code means
The negative line of vehicle communication bus F is being held low. Everything at U0083 applies, including that the body-to-chassis earth strap is the commonest single cause on this kind of vehicle and should be inspected before the bus pair is traced.
One addition belongs to this conductor: it is the one nearest the earth wiring, so a degraded body earth reaches it first — which is why the U0083 signature of a fault that follows load rather than movement shows up here most clearly.
And there is a check that separates the two possibilities in a minute. Measure the voltage between the body structure and the chassis with the body equipment running. A healthy bonding shows a few tens of millivolts. A corroded one shows volts — and volts between two parts of a vehicle that should be at the same potential is the fault, stated directly.
That is a simpler and more decisive test than tracing a network, and it is the one to ask for first on a converted vehicle showing this code.
Likely causes
Start here
- Corroded earth connection · moderate
- Wiring shorted to ground · moderate
- Poor wiring splice in an aftermarket installation · moderate
- Damaged data bus wiring · moderate
Less common
- Water ingress into connector · moderate
- Intermittent wiring fault · moderate
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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- The car — make, model, year and engine. The same fault behaves differently on each.
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