Rear Parking Aid doesn't work.
But I do get the warning beep when I select reverse.

Does this mean;
1 The fuse is good ?
2 The switch on the gear selector is good ?
3 The Control box in the boot is good (least confident about this)??

I can't hear any ticking from the sensors when Reverse is selected but I will try again later when the passing traffic dies down - how loud is it ?

 

The ERROR TONE means there is a problem with the system.
The system is on the SCP network so you could interrogate the module if you have the required diagnostic device.(that is what I do)

Most people check the sonic sensors or guess at what else could be at fault.

 

rod, based on what you are describing, you have a sensor that has failed. When you can, put the car in reverse and put your ear up to each sensor. You should hear a high pitch clicking/screeching sound. If you don't hear it, that is your bad sensor. Replace the sensor and go from there.

 

Tbh, I can't hear anything from any of them.
I have ordered a mongoose cable and SSD so hopefully that will help

 

rod_f, if you hear nothing from all 4, then you have a problem with your rear parking assist. Now, just to make sure, you turned the car on, put it in reverse and with the help of a second person, you put your ear to each sensor with the gear shifter in REVERSE? Correct? If not, then yes, the sensors will be quiet. The car has to be on and in reverse for the sensors to chirp.

 

Yes, ignition on/engine off and in reverse.
I also found the module and pulled and reinserted the 3 plugs - it all looked fine

 

rod, then odds are, that module you pulled is failed. You will need to find a new one and stick it in the car.

 

https://www.ebay.com/itm/12482578641...SABEgK45_D_BwE

 

After all that, it was a bad sensor.
It turns out sticking my ear near the sensors wasn't enough, I had to actually press my ear against the bumper to hear them.
Maybe I'm just going deaf.

 

I use my finger tip with a light touch in a circular motion.
You can FEEL the pulses as long as you keep moving your finger. If you STOP, the pules seem to stop along with it.
Probably cause interference with the transducer membrane?

 

Any mobile phone voice recorder app that has some kind of live graphical frequency display with a handsfree headset works really well. You can then hold the mic right up to each sensor and see the "blips" easily.