U0140: Lost Communication With Body Control Module
What to do
Expect an assortment of things to stop working at once — lights, central locking, windows, wipers, interior lighting, the alarm — and possibly a car that will not start.
The useful thing to know is that this is one fault, not several. A spread of unrelated electrical problems arriving together is the signature of this module rather than of a car falling apart, and chasing them individually wastes a lot of time and money.
Check your carpets, especially the front footwells, and say so if they are damp. This module sits inside the cabin, so a blocked drain, a leaking heater or a perished windscreen seal puts water straight onto it — and wet carpets with odd electrics are almost always the same fault rather than a coincidence. That is worth raising before anyone quotes for a module, because they are expensive and usually need programming to the vehicle.
If the car will not start, that is likely the immobiliser function rather than a fuel or ignition problem, so it is worth steering the diagnosis away from those.
What this code means
The body control module has stopped being heard from. The general reasoning is at U0100.
The body control module runs everything that is not the engine, the gearbox or the brakes — exterior and interior lighting, central locking, windows, wipers, the alarm, and on most vehicles the immobiliser. It is also, on many designs, a gateway between the vehicle's separate networks.
That combination is what makes this code look like several faults at once. The presenting complaint is rarely "the body control module has failed"; it is that the lights, the locks, the wipers and half the dashboard have all started misbehaving in the same week. That reads as an electrical gremlin and gets chased as several problems, and it is one module. Recognising the pattern — a spread of unrelated comfort and convenience faults arriving together — is most of the diagnosis.
Where it holds the immobiliser, the car may also not start, and that is the part that sends people in the wrong direction entirely: a no-start gets investigated as fuel or ignition while the actual fault is a module that cannot confirm the key.
One cause deserves naming ahead of the module itself, because it is common, cheap to confirm and almost never volunteered: water. This module lives in the cabin — behind the dashboard, in a kick panel, or under a seat — which puts it directly in the path of a blocked bulkhead or plenum drain, a leaking heater matrix, or a perished windscreen seal. Damp carpets and strange electrics are the same fault far more often than they are two, so a wet footwell is worth mentioning before anything is bought.
Likely causes
Start here
- Water ingress into connector · moderate
- Failed power or earth supply to the module · moderate
- Corroded or loose connector · easy
- Damaged data bus wiring · moderate
- Blown fuse or failed supply · easy
Less common
- Faulty aftermarket alarm or immobiliser installation · moderate
- Faulty body control module · specialist
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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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.
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