Parking sensor module.

[akita1]

Hi all I have a 2006 V8V which has a problem with the parking sensors when engaging reverse the R symbol lights up on the dash followed by a tone but no sensor beeping the switch in the consol lights up and sometimes stays on after engaging forward gears I have cleaned /dried the sensors and cannot hear any noise coming from them so am considering a module fault does anyone know where it is located please many thanks.