Rear parking sensors - where next

[Morph]

My rear parking sensors constantly beep so I’ve removed each one and replaced it with a known working one but is still constantly beeps. Where do I look next and can I test them for operation using a multimeter?

[TheClient]

Mine are fussy. Especially at the front for some reason. For example when wet, there was one or two that beeped constantly.  I replaced. Now 1 or two others do it when wet..... How much paint is on them?  I'd suggest trying a brand new replacement and seeing if it improves things in that position.

[Morph]

When taking a break I thought about it sensibly and realised that more than one could be broken, tomorrow I’ll change and test individual ones with one of the fronts which are working to go through the elimination process. 

[Morph]

Well I’ve got no real further in my quest. Changed front for backs and still have the same problem. The rear does work but as soon as a sensor is activated it then beeps continuously and doesn’t stop or settle down to shorter beeps. 

Also I forgotten how it works normally, if you are nowhere near anything does it still give short beeps or nothing?

Edited 24 April, 2021 by Morph

[drw8]

Have your tried going out to the car late at night (when it's nice a quiet) and then putting something like a screwdriver /punch etc against it and sticking it to your ear? Should hear clicking from a working sensor. 

[Morph]

2 hours ago, drw8 said:

Have your tried going out to the car late at night (when it's nice a quiet) and then putting something like a screwdriver /punch etc against it and sticking it to your ear? Should hear clicking from a working sensor. 

Yeah they all seem to click. 

[Guest]

When reverse gear is selected you should hear one short beep and silence until something comes into range.

 

If all sensors are working the only other things to check are the wiring and PDC unit.

 

If you have a decent diagnostic tool you can see what distance each sensor is sensing and if the PDC unit is reporting any fault(s).

[TheClient]

To me it seems like sensors. When you sat you moved them around, did the fault follow the sensor or stay where it was located? As @MicMacsays run diagnostics, listen, when something is a certain distance away I get no beeps. Silence until reasonably close. 

[Morph]

Thanks for your reply’s. I completely stripped it all out, T cut and really cleaned the sensors, set it up in the boot and they are now working. I’ll check again tomorrow and then Just got to get it all back together.  
I only have the basic diagnostic tools which I appreciate makes things more difficult. 

Edited 24 April, 2021 by Morph