Some 12 months ago I began to have intermittent problem with parking sensors beeping erratically. This eventually settled into always getting a 5 second bleep on engaging reverse, a standard fault warning. I have now decided to fix this, but am having problems.

By this time none of sensors were ticking, so I first replaced all four sensors (Part no 66206989067 Parktronic Sensors bought from Lightec24 through, approx £20 each - delivered within 3 days from Germany!) These are, I believe, new, came in original packing & are identical to those replaced. I did not want to fit used ones, typically from e-bay, as they appear to have limited life due to wear, tear, & moisture ingress.

All are now ticking, but not warning of proximity by beeping. I do not now get 5 second fault-warning beep when engaging reverse, but beeper is not faulty - if I unplug sensor loom from control unit then I do get beep.

I temporarily replaced control unit part no 21-6921-415 with a used unit, albeit with different part no 21-6916-405. This is still supposed to be OK for my model, although I have not been able to identify difference, if any No change!

No obvious damage to wiring loom, & in any case would then expect to have 5 second beep

Has anyone any other suggestions. Is it possible that Control Unit now needs reprogramming. If so, am I right in thinking that just to plug it in & diagnose fault is around £50?