Dear Team,

Sudden failure of the parking sensors and a long beep when the ignition goes on. GAP tool shows "U0252-00 (2F) Lost communication with the rear lighting control module B"

The live values for all the sensors are stuck at 2.5m.

Also "B10EA-14 (2F) Positive temperature coefficient heater - General electrical failure - circuit short to ground or open"

Suggestions (other than "Burn it!") appreciated, thank you.

On the rear off side behind the bumper is the wiring loom from the rear sensors , there is a connector for the bumper sensor loom , quite high up . It is susceptible to corrosion due to its position. so it’s one place to start . 2009 GS Auto Zermatt Silver - Sold June 21 after 10 years of ownership

2016 Subaru Outback SE 2.0 diesel SE Premium Lineartronic Sold 2024 after 8 years and 80k miles . Best Car I ever owned !

2023 Toyota Hilux invincible X 2.8 Auto .

PCT heater is a common problem. Mine hasn't worked since getting it 4 years ago.
It's often the PCT heater itself at fault, but can also be fuses or the relay. Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

No, it's all much odder than that.

The fault will not clear and I get the long "beeeep" four seconds after the engine starts to let me know the rear sensors aren't working. But...

If I start the engine and immediately go into reverse, the sensors correctly report the proximity of the garage door for four seconds - and then go silent. So they are working, it's the module deciding otherwise.

Everything else is working correctly at the rear - almost. The tow hitch was fitted a year ago using all the correct items (Witter and Hella) but initially using the trailer indicators resulted in a rapid flash. Telling the black box that a tow hitch was fitted made the indicators run at the correct speed, but I've never had the trailer light repeat indication work. This may be relevant or a red herring.

How can I make the rear body control module stop deciding that the parking sensors aren't working when they definitely can and would if it would let them?

The BCM takes all the data from the various data busses and sends it to where it's supposed to be going. There isn't a rear BCM, just the main unit behind the glove box, which LR call the CJB, short for central junction box.
The PDC module is behind the LH boot panel, quite close to the towing ECM, they even share some wiring and a grounding point.

I'd be tempted to take a look to make sure everything is as it should be. Does the vehicle have front PDC too? Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

Hi there,
Did you ever find a fix to this?
I am having exactly the same issue.
Sensors will work for a few seconds if I put it into reverse immediately and then long beep and they are inactive. I'm assuming it's sensing a fault somewhere and am disabling them.
I have checked the connector to the wiring loom in the rear bumper and there is no corrosion. I can not read live data to the sensors as they are inactive as soon as I turn the ignition on.

Please help 😁

I'm stuck with it. Local indy spend some hours with his diagnostic kit getting no further than I had with my ID tool (but at least the resultant bill was £0). His crestfallen advice was to try an automotive electrical specialist, but they're a bit uncommon in rural Suffolk.

It's not a fault with the sensors, it's definitely a module issue - it makes so sense for the system to claim it's lost comms with the module when everything the module runs is working (except the rear sensors, which demonstrably do work until the module shuts them down).