U0010 Moderate Generic / SAE

U0010: Medium Speed CAN Communication Bus

Network and Communication Bus Signal and Bus Off

What to do

The car will almost certainly drive normally. Expect the electrical fittings to misbehave instead — locks, windows, mirrors, interior lighting, the dashboard display — and probably several of them at once.

That spread is the point rather than a coincidence. Modern cars have more than one internal network: a fast one for the engine and gearbox, and a slower one for everything to do with the body, because a door lock does not need millisecond timing. This code is the slower one, so a group of unrelated electrical things failing together is one network fault rather than several broken parts.

And knowing which network it is tells you where to look. This one runs to the doors, the seats, the tailgate and the boot — so its faults are water and flexing faults, not engine-bay ones.

Two things are worth checking yourself before anything is booked in.

Are your carpets damp, or is there water under the boot floor? Wet footwells and odd electrics are usually the same fault.

And does the fault change as a door or the tailgate is opened and closed? The wiring passes through a rubber concertina that is flexed every single time, and it breaks inside insulation that still looks perfect.

Before driving at night, check that your lights, indicators and brake lights all still work.

What this code means

A fault has been detected on the medium speed data bus. U0003 covers the electrical faults that repeat on every bus in this range; this page covers what makes this particular network different.

A vehicle has more than one bus because its traffic is not all equally urgent. A torque request between the engine and the gearbox has to arrive within milliseconds. A door lock does not. So the body, comfort and convenience systems sit on a slower network — cheaper transceivers, longer permissible runs, more nodes, less demanding wiring.

And that decision determines where this bus fails, which is the useful part.

The high speed bus lives in the engine bay and under the floor: its enemies are heat and vibration. The medium speed bus goes to the doors, the seats, the tailgate and the boot — and its enemies are water and flexing. Every argument the corpus makes about door harness boots, blocked door drains, tailgate hinges and wet boot floors applies to this network and not to the other one.

So the symptoms cluster in the body rather than the powertrain. The vehicle usually drives perfectly while locks, windows, mirrors, lighting and the instrument display misbehave together — and a spread of unrelated body electrical faults arriving at once is this bus rather than several failed modules.

One caution about applying U0003's resistance test here, because getting it wrong wastes an afternoon. The 60 ohm figure is a high speed CAN figure, arising from two 120 ohm terminators at the ends of that backbone. Medium and low speed networks are terminated differently — often at every node, often at quite different values — so a reading that would condemn a high speed bus can be entirely normal here. Use the manufacturer's figure for this network, not the familiar one.

The single reading that does carry across is a dead short: near zero ohms is wrong on any bus.

Likely causes

Start here

Damaged data bus wiring · moderate
Broken wire in the door harness boot · moderate
Water ingress into connector · moderate
Corroded or loose connector · easy

Less common

Another module holding the bus down · specialist
Poor wiring splice in an aftermarket installation · 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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The car — make, model, year and engine. The same fault behaves differently on each.
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