rear parking sensors

[akita1]

Afternoon all I have an intermittent problem with my rear parking sensors ( 2006v8v) recently they stopped working altogether today they are working again but the sounder doesn't seem very loud compared with before I have cleaned the sensors and checked the fuse as its now working again I think the fault might be the module can anyone point me in the direction of where the module is located? many thanks.

[Manwhoneverwas]

Its behind the passenger seat at the floor level, you have to remove the rear trim similar to fitting a new battery.
Its actually a Jaguar part, but I was led to believe cheaper from Aston Martin dealers.
Price is circa £119 +VAT from memory