U0036: Vehicle Communication Bus A (-) Shorted to Bus A (+)
What to do
Expect a set of systems to have stopped completely rather than working badly, and possibly a garage saying their diagnostic tool cannot connect.
The two wires carrying this network are touching each other. Because they carry the same message in opposite directions, joining them cancels it entirely — so the network stops rather than degrading.
There is one useful thing about this particular fault: it can be confirmed without any manufacturer data at all. A dead short reads close to zero ohms across the pair, and that is wrong on every network there is. Most measurements on a lettered network need the manufacturer's figures first; this one does not.
Two wires twisted together only touch for physical reasons, and the list is short. A loom crushed by a panel, a bracket or a fixing. A screw put through the harness during a repair or an accessory installation. Water bridging a connector. Rodents.
Do not let computers be replaced — they are almost certainly all fine.
What this code means
The two lines of vehicle communication bus A are shorted together. See U0009 for why joining a differential pair cancels the signal completely, and for the short list of physical causes.
This is the one fault on a lettered bus that can be confirmed without identifying the network first, and that is genuinely useful.
U0028 explains that nothing about a lettered bus can be judged until it is identified — its resistance figure, its acceptable error rate, even which modules are on it. A dead short is the exception. Near zero ohms across a pair is wrong on every network there is, whatever its speed, medium or terminated value.
So this fault can be proved with a meter and no reference data, which shortens the diagnosis considerably. Identifying the network is still needed to find the wiring, but not to establish what is wrong.
And the causes remain physical and short: a loom crushed by a panel, a bracket or a fixing; a screw or self-tapper put through a harness during a repair or an installation; water bridging a connector; rodent damage that stripped both conductors at one point.
Likely causes
Start here
- Bus wires shorted together · moderate
- Damaged wiring harness · moderate
- Water ingress into connector · moderate
- Damaged data bus wiring · moderate
Less common
- Poor wiring splice in an aftermarket installation · moderate
- Corroded or loose connector · easy
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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