U0045 High Generic / SAE

U0045: Vehicle Communication Bus B (-) Shorted to Bus B (+)

Network and Communication Bus Signal and Bus Off Emissions related

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, which cancels the signal entirely — so the network stops rather than degrading.

One useful thing: this can be confirmed with a meter and no manufacturer data at all. A dead short reads close to zero ohms across the pair, and that is wrong on every network there is.

And the search is shorter than it sounds. Most of a network's length is the main run down the car, with only short tails to each computer — so a crush or a screw through a loom is far more likely to have found the main run. The places to look are where that run leaves a protected route: through the bulkhead, along a sill under the trim, across the floor under a seat rail, through a door concertina, over the tailgate hinge.

That is a short list rather than the whole car, and mentioning any work done in those areas — trim off, seats out, carpets lifted, a stereo or tow bar fitted — narrows it further.

What this code means

The two lines of vehicle communication bus B are shorted together. See U0009 for why joining a differential pair cancels the signal completely, and U0036 for why this is the one fault on a lettered bus that needs no manufacturer data to confirm.

One thing follows from U0037 and is worth stating, because it narrows the search usefully.

The backbone runs the length of the vehicle; the stubs to individual modules are short. So the great majority of a network's physical length is backbone, and a crush or a fastener through a harness is far likelier to find the backbone than a stub.

Which means the search should follow the backbone's route — obtained from the same wiring diagram needed to identify the bus at all — rather than working outward from whichever module happens to be nearest.

And the places a backbone is vulnerable are the ones where it leaves a protected run: through a bulkhead grommet, along a sill under a trim panel, across the floor beneath a seat rail, through a door boot, over a tailgate hinge. Those crossings are where the crushes and the screws are, and they are a short list rather than the whole vehicle.

Likely causes

Start here

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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