U0041: Vehicle Communication Bus B (+) High
What to do
This is one of the faults that can damage things rather than just stopping them. Battery voltage has got onto a network wire connected to every computer on that network. Be prepared for a repair in two stages, as at U0005.
One thing is worth raising immediately: has anything been connected to the car's network after it was built? A tracker, insurance box, dashcam, fleet device, alarm or aftermarket stereo.
Those installations are the likeliest cause of this particular fault, and the reason is physical. An added device needs a power feed as well as a data connection, and the two get run together — often in the same sleeve and the same plug. So the live wire and the network wires end up lying against each other for the whole of that run, which is exactly the condition needed for this fault. And a home-made loom rarely has the separation and protection a factory one does.
Say what has been fitted, including by a previous owner, and ask for it to be unplugged and the car re-tested. That is quicker than any measurement.
And ask for the car's network map to be read before the repair, so there is a record of which computers were exposed.
What this code means
The positive line of vehicle communication bus B is being held high. Everything at U0032 applies, including the module-damage warning from U0005 and the argument for establishing the vehicle's topology before the repair rather than after.
One addition belongs here because it follows U0037: a network with an added device is more exposed to this fault than one without.
An accessory connected to the bus needs a power feed as well as a data connection, and those two are run together — often in the same sleeve, often terminated in the same connector block. So the live and the bus pair are physically adjacent for the whole of that run, which is the condition this fault requires.
And the installation is rarely the manufacturer's, so the separation, sleeving and strain relief that keep power away from data in a factory loom are frequently absent.
So on a vehicle with anything spliced onto the network, that installation is the first place to look rather than the last — and unplugging it is quicker than any measurement.
Likely causes
Start here
- Poor wiring splice in an aftermarket installation · moderate
- Wiring shorted to voltage · moderate
- Faulty aftermarket alarm or immobiliser installation · moderate
- Damaged data bus wiring · moderate
Less common
- Damaged wiring harness · moderate
- Corroded earth connection · 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
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