U0087: Vehicle Communication Bus F (-) High
What to do
Isolate the body equipment and do not operate it until this is fixed — see U0084. Battery voltage on a network wire damages the computers connected to it, and on a converted vehicle the current available is much greater than on a car.
One thing is worth knowing, because it saves a lot of searching.
On a converted or commercial vehicle, four different network faults can all come from one place: the electrical join between the body and the chassis. A corroded earth strap causes two of them; wiring routed across that join causes the other two.
So that join is not one suspect among many — it is by far the most productive place to look, and inspecting it properly comes before tracing any wiring.
Two quick tests to ask for. The voltage between body and chassis with the equipment running — whole volts means a corroded bond. And disconnecting the body equipment and re-checking, which isolates half the wiring in one step.
Contact whoever converted the vehicle, since that wiring and that join are their work.
What this code means
The negative line of vehicle communication bus F is being held high. Everything at U0084 applies, including that the current available on a converted vehicle makes the module-damage warning at U0005 an expectation rather than a possibility.
And U0086's body-to-chassis measurement is the test to run first here too, because a badly bonded body can put voltage onto this conductor as readily as a chafed live can — and it is the cheaper of the two to check.
One thing closes the argument this whole group has been building. On a converted vehicle, four different faults — U0083, U0084, U0086 and this one — can all originate in the same place: the electrical join between the body and the chassis. A corroded earth strap causes two of them, and wiring routed across that join causes the other two.
So the join is not one item on a list of suspects. It is the single most productive place to look on this kind of vehicle, and inspecting it properly before tracing anything is the shortest route to all four.
Likely causes
Start here
- Corroded earth connection · moderate
- Wiring shorted to voltage · moderate
- Poor wiring splice in an aftermarket installation · moderate
- Damaged data bus wiring · moderate
Less common
- Damaged wiring harness · moderate
- Physical damage from road debris · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about U0087.