U0022 Moderate Generic / SAE

U0022: Low Speed CAN Communication Bus (+) Low

Network and Communication Bus Signal and Bus Off

What to do

Everything may work most of the time, and misbehave now and then. That pattern is the clue rather than a nuisance.

This part of your car's network can run on one wire if the other fails, so a fault here often hides completely. But where the problem is a partial short rather than a clean break — usually damp — the car can switch back and forth as conditions change.

So the useful thing to notice is not what fails but when.

Does it misbehave only after rain? Only in the mornings? Only after the car has been washed or parked under trees? Any of those answers narrows the search to the places water actually reaches, which is a far shorter list than the whole network — and it is information no workshop can obtain on a dry day.

Write down what you notice and give it to the garage. "Only after rain" is worth more than an afternoon of testing.

While you are at it: lift the carpets and feel underneath, check under the boot floor, and listen for sloshing in a door.

What this code means

The positive line of the low speed data bus is being held low. See U0004 for the short-to-earth argument, U0013 for why water leads the causes on the body networks, and U0019 for the single-wire fallback that hides all of this.

One thing is specific to a short rather than a break on a fault-tolerant network, and it is worth knowing because it affects what the driver sees.

Switching to single-wire operation is not instantaneous or perfectly silent. The network detects the fault, decides, and changes mode — and on a bus already carrying a partial short, that decision can be made and unmade as conditions change. Damp that comes and goes with the weather is exactly such a condition.

Which produces the presentation worth recognising: body functions that work perfectly for days and misbehave for an hour after rain, with a code stored throughout and nothing reproducible in a workshop.

That is not an elusive fault. It is a wet connector, and the useful thing a driver can supply is the weather rather than a description of the symptom. "Only after rain" or "only in the mornings" narrows the search to the places water reaches, which is a much shorter list than the network's whole length.

Likely causes

Start here

Water ingress into connector · moderate
Wiring shorted to ground · moderate
Blocked door drain letting water into the module · moderate
Intermittent wiring fault · moderate

Less common

Damaged data bus wiring · moderate
Corroded or loose connector · easy

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

Be the first to write this up

Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.

What makes one worth reading:

The car — make, model, year and engine. The same fault behaves differently on each.
What you measured, not only what you replaced.
What actually fixed it — or that nothing did, which is worth knowing too.