U0243 Moderate Generic / SAE

U0243: Lost Communication With Parking Assist Control Module B

Network and Communication Lost Communication (continued)

What to do

The car drives normally; the parking sensors at one end will have stopped working.

One thing to check before assuming a fault: are the sensors clean? They are the small round faces in the bumper, and packed mud, snow, ice or a heavy coat of road film stops them working entirely. So does a towbar, bike rack or trailer socket sitting in the way. Washing them is free and fixes a good proportion of these.

The safety point worth knowing: on many cars these same sensors also brake the vehicle automatically at low speed — the system that stops you reversing into something, or someone. If your car has that, assume it is not working and reverse as though nothing will stop you. Be especially careful reversing where children might be.

Mention any bumper work — a parking knock, a respray, a towbar fitted, an accident repair. All of them disturb these sensors and their wiring, and a respray over a sensor face will stop it working permanently.

What this code means

The second parking assist control module has stopped being heard from. See U0200 for the block's framing.

A second parking assist module normally means the front and rear systems are controlled separately, so the practical question is which end has gone quiet — and the answer is usually obvious from which sensors have stopped responding.

The safety framing here is different from the blind spot systems at U0232, and the difference is worth being precise about. Parking sensors operate at very low speed with the driver looking around anyway, so the consequence of losing them is a reversing manoeuvre done the way it was done for decades — genuinely manageable, unlike losing blind spot warning at motorway speed.

But there is one exception that matters and it is easy to miss: on many vehicles these same sensors feed low-speed automatic braking. A system that stops the car before it reverses into a bollard or, far more importantly, a child behind the vehicle. Where that is fitted, this code disables it — and a driver relying on the car to stop should know it will not.

The commonest cause is not electrical. Ultrasonic sensors are open to the road at bumper height. Packed mud, ice, snow, a thick coat of road film, or a badly applied respray covering a sensor face all stop it working, and so does a towbar, a bike rack or a trailer socket obstructing the field. Cleaning the sensor faces is free and resolves a good share of complaints.

And a bumper is the most frequently damaged and refitted panel on any vehicle. A parking knock, a respray, a towbar installation or an accident repair all disturb these sensors and their wiring — so recent bumper work is the first question after cleanliness.

Likely causes

Start here

Corroded or loose connector · easy
Water ingress into the module connector · moderate
Physical damage from road debris · moderate
Disconnected sensor connector · easy

Less common

Damaged wiring harness · moderate

Symptoms

Components involved

Information, not instruction

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Community experience

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