2005 E53 PDC not working

[PLH-BMA]

Hi everyone , Im a new member, recently purchased 2005 X5, absolutely love the car!!! Had quite a few niggles with different things not quite as they should be, but have sorted everything except for PDC !!! Ive read numerous posts on forums about this problem but none seem to answer the question!! When selecting reverse the pdc light flashes and a long single beep, which sounds like its from the rear, the light continues to flash when selecting Drive for a short time! Ive tried the recommended listening to the sensors for ticking whilst the system is in operation, with nothing from any sensor front or rear.
I purchased and fitted a second hand PDC module with exactly the same results !!
Am i to believe that all 8 sensors have failed or am i missing something?
Hope you super techy people out there can help!!
Cheers
Paul