U0168 Moderate Generic / SAE

U0168: Lost Communication With Vehicle Security Control Module

Network and Communication Lost Communication

What to do

The alarm has stopped working properly. The car still starts and drives — that is the immobiliser, which is a different system.

Two things can happen, and one of them is much more annoying than the other.

The alarm may simply not arm. The car locks normally, but nothing is watching it. The clue is that the usual flash or chirp when you lock is missing — worth knowing before you leave it somewhere you would rather not.

Or it may go off by itself, usually at three in the morning. When the alarm computer stops hearing from the modules watching the doors, the bonnet and the boot, it cannot tell a real opening from a lost message — and an alarm's safe assumption is that something happened.

If that is what yours is doing, ask for the bonnet switch to be checked first. It is by far the commonest cause of alarms going off on their own: it sits in the engine bay, it corrodes, and it gets knocked out of adjustment by washing and servicing. It is also cheap.

One warning: do not try to silence a going-off alarm by disconnecting the battery. The siren has its own internal battery precisely so that this does not work, and on many cars disconnecting sets it off. There is a proper disarm procedure — ask for it rather than forcing it, because a siren forced into protection mode may have to be replaced.

What this code means

The vehicle security module has stopped being heard from. The general reasoning is at U0100, and U0427 covers the same module reporting implausibly instead.

This is the alarm rather than the immobiliser, and separating the two saves a great deal of confusion. The immobiliser at U0167 stops the vehicle being driven; the alarm at this code makes a noise and flashes lights. A vehicle with an alarm fault normally still starts and drives.

Silence here fails in two opposite directions, and the second is what brings people in.

It may not arm at all — the vehicle locks, nothing is watching it, and the only way to know is that the usual confirmation flash or chirp is missing. Worth knowing before parking somewhere you would rather not.

Or it may go off by itself, repeatedly, usually at night. A security module that has lost contact with the modules watching the doors, the bonnet and the boot cannot tell a genuine opening from a lost message, and the safe assumption for an alarm is that something happened. That is the version that makes a car unwelcome where it is parked, and it is worth treating as urgent for social reasons rather than mechanical ones.

Two practical facts about alarms that people are rarely told.

The siren usually has its own internal battery. Disconnecting the vehicle's battery does not silence it — that is the point of it — and on many designs doing so triggers it. There is normally a documented disarm procedure, and forcing the issue can leave a siren that has to be replaced.

And the bonnet switch is the leading cause of self-triggering alarms by a wide margin. It lives in the engine bay, it corrodes, and it gets bent out of adjustment by every wash and every service. It is cheap and it is the first thing to look at.

Likely causes

Start here

Corroded or loose connector · easy
Faulty aftermarket alarm or immobiliser installation · moderate
Blown fuse or failed supply · easy
Water ingress into module · moderate

Less common

Damaged data bus wiring · moderate
Low system voltage · 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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