U0252 High Generic / SAE

U0252: Lost Communication With Lighting Control Module — Rear B

Network and Communication Lost Communication (continued)

What to do

Do this before anything else: get somebody to stand behind the car while you press the brake pedal, work the indicators and turn the lights on. Two minutes, no equipment, and it tells you whether this is urgent.

If the brake lights or indicators are out, the car is not roadworthy and should not be driven — a car that does not show brake lights gets hit from behind, and you have no way of knowing from the driving seat.

If everything still works, this is less urgent but still worth booking in, since it may be part of the lighting that only shows in the dark.

Two things worth mentioning. Has a towbar or trailer electrics ever been fitted? Badly installed towing wiring is one of the commonest causes of rear lighting faults. And is there any sign of water in a rear light unit — misting, or a damp boot floor? These lamps sit low in the road spray and their seals age.

One question worth asking before agreeing to a repair: is it the module or the lamp? On many modern cars the rear lights are LED units that cannot be repaired separately, so the difference between those two answers is a lot of money.

What this code means

The second rear lighting control module has stopped being heard from. See U0200 for the block's framing and U0241 for the headlamp equivalent.

Rear lighting is where a network fault becomes a roadworthiness and a safety matter, and the reason is that you cannot see your own rear lights. A failed headlamp announces itself the moment it gets dark. A failed brake light, tail light or indicator is invisible from the driving seat, and the first indication is often somebody else's reaction — or a police stop.

What is at stake, in order:

Brake lights. The single most important signal the vehicle sends, and the one whose absence causes rear-end collisions. Modern lamps are frequently LED arrays driven by this module rather than simple bulbs, so a module fault can extinguish them entirely with no bulb having failed.
Indicators, whose loss is both a hazard and an immediate roadworthiness failure.
Tail and position lamps, making the vehicle invisible at night from behind.
Reversing and fog lamps, less critical but still required equipment.

So the first action is to have somebody stand behind the car while the brake pedal, indicators and lights are operated. That takes two minutes, needs no equipment, and establishes whether this is an urgent problem or a minor one — and it is the single most useful thing on this page.

One thing specific to LED rear lighting is worth knowing before a quote is accepted: on many vehicles the LEDs are not serviceable separately, so what would once have been a bulb is now a complete lamp assembly. That makes establishing whether the module or the lamp is at fault worth real money, and it is a fair question to ask before either is ordered.

Causes concentrate on water and towing electrics. Rear lamp units sit low, take road spray directly, and their seals age; and anything spliced in for a towbar is a leading cause of rear lighting faults — a badly installed bypass relay or a connection made into the lighting circuit rather than through one is an ordinary finding.

Likely causes

Start here

Water ingress into the module connector · moderate
Corroded or loose connector · easy
Faulty aftermarket alarm or immobiliser installation · moderate
Damaged wiring harness · moderate

Less common

Failed power or earth supply to the module · moderate
Blown fuse or failed supply · 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

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The car — make, model, year and engine. The same fault behaves differently on each.
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