U0013 Moderate Generic / SAE

U0013: Medium Speed CAN Communication Bus (+) Low

Network and Communication Bus Signal and Bus Off

What to do

The car will almost certainly drive normally. A group of electrical fittings will have stopped working.

Look for water before anything else, because on this particular network it is the leading cause by a distance.

Lift the carpets in the footwells and feel underneath. Lift the boot floor and look under the spare wheel. Listen for sloshing in a door.

Water in a connector does not have to short anything to stop the network — damp road grit conducts quite well enough.

And if the fault appeared after heavy rain, a car wash, or the car being parked under trees for a while, say so. That is a strong clue, and finding the water is the actual repair rather than a step on the way to one.

Common sources: door drain holes blocked with grit so the door fills up, a blocked drain at the base of the windscreen soaking a footwell, a leaking heater, an aged tailgate seal, or a sunroof drain emptying down the inside of a pillar.

Check your lights and indicators before driving at night.

What this code means

The positive line of the medium speed data bus is being held low. See U0004 for the short-to-earth argument and the voltage signature, and U0010 for what this network carries.

On this bus, water outranks chafing as a cause, and that reverses the usual search order.

The high speed bus lives in dry places and fails by abrasion. This one goes into doors, under seats and into the boot — and a connector with water in it does not need to be shorted to the body to pull a bus line down. It only needs a conductive path, which damp road grit provides.

So the diagnosis starts with the wet places rather than with a meter. Door drain holes blocked with grit so the door fills instead of draining; a boot floor with standing water under the spare wheel; a footwell soaked by a blocked bulkhead drain, a leaking heater matrix or a perished screen seal; a sunroof drain emptying down the inside of a pillar.

A fault that appeared after heavy rain, a car wash, or a period parked under trees is that — and finding the water is the repair rather than a preliminary to it.

Likely causes

Start here

Water ingress into connector · moderate
Blocked door drain letting water into the module · moderate
Wiring shorted to ground · moderate
Damaged data bus wiring · moderate

Less common

Corroded or loose connector · easy
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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