U0142 Moderate Generic / SAE

U0142: Lost Communication With Body Control Module B

Network and Communication Lost Communication

What to do

Expect a group of electrical things in one part of the car to have stopped working.

Start where U0141 does: ask for the fuses and relays nearest the dead area to be checked first. These computers sit beside their own fuse box, so one blown fuse can take out the whole area, and that is far cheaper than a module.

Then, if the fault comes and goes rather than being permanent, pay attention to when. It matters more than it sounds.

If the car seems to forget its settings every time you switch off, that points at one particular supply.
If everything is remembered but nothing works, that points at another.
If it only misbehaves when a lot is switched on at once — headlights, heated screen, blower on full — that is a corroded earth connection, and it is a cheap fix that is very hard to find without that clue.

Write down what you notice and give it to the garage. "It only does it with the lights and heated rear screen on" sounds like nonsense and is actually a precise description of the fault.

Check your carpets for damp while you are at it, and check the lights work before driving at night.

What this code means

A body control module has stopped being heard from. See U0141 for why the fuse box beside the module is the first thing to check, and U0443 for what the letters mean.

One addition belongs here rather than at U0141, because it explains a fault that comes and goes rather than one that has simply stopped.

A module wakes and sleeps. It is not powered continuously in the way a lamp is: it holds a permanent live for memory and a switched live for operation, and it decides — with the rest of the network — when the vehicle may power down. So there are three supplies to lose rather than one, and losing each produces a different picture.

Permanent live lost: the module forgets its settings and configuration every time the vehicle is switched off, and behaves like a new one each morning.
Switched live lost: the module remembers everything and never operates.
Earth degraded rather than lost: the module works when little else is drawing current and drops off when it is. That is the intermittent, and it is a corroded earth stud rather than a module.

The third is the one worth naming, because "it only does it when the headlights and the heated screen are on" sounds like nonsense and is a precise description of a bad earth. A driver who has noticed a pattern like that should say so; it is worth more than any test.

Likely causes

Start here

Less common

Intermittent wiring fault · moderate
Damaged data bus wiring · 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

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.