parking sensors issues!!

[Adensar]

Hello

I am trying to find out the best way o finding out swhich sensor is faulty in my front bumper of my 2001 X5 UK model. Sometimes all works fine but most of the time when activating the sensors for parking i just a get a cotinuous audible sigaal even when i am not close to anything. I am sure it is a problem with a front sensor as the tone of the noise matches that of the front sensors signall when all is working. I have tried the obvious way of manually blocking each sensor but was wondering if there is anyway of electrically testing each sensor to be sure which one to change.

Any ideas welcome.

Thanks