the best way to test the sensors is with a mechanics stethoscope about 5 ponds on ebay, if the sensors are all working you will here a distinct rapid clocking noise from each one when forward or reverse is sected. On my 2005 2.7 I have a duel module in the boot that has plugs for front and back. In my case the red overhead warning light is on, I have a single front sensor not working, but the rears click but do not work, I am trying to find out... If one front sensor will knock the whole system out (front and rear) if you can change out the front outside sensors without removing the front bumper. If you live in kent we could meet up and try to sort them out. I have a spare loom and can test sensors by plugging into my car Stan stan