Parking Ecu

Have a problem with my 56 plate td4 sport. Recently had a parking sensor fail.would beep when reverse gear selected then make another long beep to say there was a problem. Listened for the clicking from sensors individually and found the culprit, a failed sensor...Dropped rear bumper and replaced, problem sorted. Been working fine for a few months. Now it’s happened again except all of the sensors have failed. When reverse gear is selected I get the beep and another continuous beep to say there’s a problem. None of the sensors are making a clicking noise. Have checked fuse. Have replaced parking Ecu as the old one the speaker was a little muffled anyway and checked wiring. All is fine. Have power to Ecu. Only difference with the new Ecu is it no longer makes the second continuous beep to indicate a problem yet all sensors don’t work. I find it hard to believe that all 4 have failed especially with one of them only being a few months old and a genuine part. Anyone have any other ideas before a drop the rear bumper again and waste cash on 4 new sensors. Thanks in advance Dave

Maybe the parking ECU went wrong and damaged all the sensors?

I replaced my rubbish BMW sourced PDC system with a cheap Chinese replacement, getting a complete kit for under £10.