U02B5: Lost Communication With Front Radar Module B
What to do
Some of the driver assistance may still work, and that is the thing to be careful about. With one of two radars missing, adaptive cruise and emergency braking can carry on partly working while the wide-angle coverage that catches vehicles cutting in has quietly stopped. Treat all of it as unavailable until it is fixed.
Check the obvious first, because it is free: packed snow, ice, mud or a thick layer of road film across the front of the car, and anything fitted in front of the radar — a badge, a number plate surround, a light bar or a towing eye cover.
Mention any front-end work or parking knock, however minor. These sensors are aimed to a fraction of a degree behind the bumper, and nothing has to look damaged for one to be moved or disconnected.
If any of it is replaced or disturbed, insist on recalibration. A radar aimed slightly wrong still works, which is worse than one that does not.
What this code means
The second front radar has stopped being heard from. The family's framing is at U0100.
The letter is the useful part of this code. A vehicle with a B radar has more than one, and that is a design decision worth understanding: a single long-range radar behind the badge sees far but narrowly, so a second unit — shorter range and much wider — is added to see what is about to cut in from the side. Some vehicles instead place B at a corner for cross-traffic alerts when reversing out of a space.
So losing B does not disable everything. Adaptive cruise and emergency braking may still function on the remaining radar while the wide-angle behaviour quietly stops — and that partial capability is exactly what makes it worth knowing about, because a system that mostly works is one a driver keeps trusting.
Where a radar fails is unlike anywhere else on a car, and the causes are ordinary rather than electrical. It is mounted behind a bumper skin or a badge, looking forward through plastic, which means:
- A knock while parking moves it. Alignment is measured in fractions of a degree, and nothing needs to be visibly damaged.
- Bumper repair, respray or a replacement grille disturbs it, and a radar that has been off the car and back on has not been calibrated unless somebody did it deliberately.
- Dirt, packed snow, ice or an aftermarket badge, light bar or number plate frame blocks it. The unit reports being blocked; a unit that has stopped reporting at all is the electrical case.
The distinction between blocked and silent matters. A blockage sets its own message and clears when the obstruction is removed. This code is silence on the network — supply, earth, connector and bus wiring, in that order.
Likely causes
Start here
- Corroded or loose connector · easy
- Damaged wiring harness · moderate
- Radar sensor not calibrated after front-end work · specialist
Less common
- Damaged data bus wiring · moderate
- Failed power or earth supply to the module · moderate
Symptoms
Components involved
Information, not instruction
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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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