Doesn't tell you which is broken though, I had two failed sensors and got the right information in the car, e.g. something wrong at the front. Only a Fault Code reader would be able to determine exactly which sensor is faulty (not all FCRs can).

Listening to (or feeling) clicking is another (not foolproof) way of diagnosing an individual failed sensor. 

"Roads ? Where we're going there are no roads." Back to the future.

rrsboy wrote:

38.4 kHz is about twice the limit of human hearing

from Bobby, an easier way to diagnose a fault:

"The parking aid module has a diagnostic connection via the medium speed CAN to enable faults to be retrieved using a Land Rover approved diagnostic system. Additionally, an on-board diagnostic routine within the parking aid module constantly monitors the system and alerts the driver to a system fault by emitting a tone from the front or rear sounder, depending on the fault.

If a parking aid system fault has occurred, the parking aid module will relay the occurrence of the fault to the driver in the following ways:

*The status LED will flash at a frequency of 2Hz if the system is active and fault is detected in the sensors, sounders, related wiring or the module.

*The front sounder will emit an error tone for 3 seconds at a frequency of 1500Hz if a fault is detected with the front sensors or the rear sounder develops a fault.

*The rear sounder will emit an error tone for 3 seconds at a frequency of 1500Hz if a fault is detected with the rear sensors, the switch, the LED in the switch or if there is a CAN bus error."

That and the fact the bloody PDC thing doesn't work at all

When my PDC failed I didn't get any of the automatic diagnostics described in RRSboy's post from Bobby, no flashing PDC light, no long tone I had a wiring loom fault so I don't know whether that makes a difference?

I am now wondering what the 'clicking noise' that people describe when you put your head next to the parking sensors actually is? Given that the pulse generated by the sensor is ultrasonic and above the range of human hearing I wonder if the click is something inside the sensor that generates the ultrasound or whether the fact that you have your ear up to the sensor means that you are able to detect a difference in air pressure as the ultrasound is emitted?? I am certain that this is largely irrelevant and will serve no good purpose in my life but I am now intrigued...