Rear parking assist problem

[Schorly]

My 2009 Golf has developed a problem with the OEM fitted rear parking assist system. When I switch in to reverse the shorter beep is heard followed by a longer lower sounding on and then nothing. The sensor don't  seem to pick up anything. Any ideas on finding out what is wrong? Sensor or control unit? Maybe wiring? It was working in the morning and developed the fault in the afternoon.

[Eddie-NL]

vcds scan would identify what the problem is

[Schorly]

I haven't got one of those and I am not keen spending loads at the dealer

[Eddie-NL]

find someone with vcds who can do a scan

the problem with OEM sensors is that if any one item fails it will knock out the whole system

Problems could be

Faulty Sensor / s
Faulty Buzzer
Damaged wiring
Faulty Module - probably not in your case

[Schorly]

should I get one sensor and swap them over until I find the broken one. If it is the sensor?

[Schorly]

Did a bit shifting about and the situation is now, that I can hear a faint ticking noise in one of the sensors. So I swapped the 'good' one to a position where I didn't hear a ticking noise and it stopped working. Plugging the sensor, which did not work in to the working position stared working. I only did this on one sensor position, but would suspect the same on the other. It is difficult to get the middle sensors out. There is a plug between the harness for the sensors and the harness to the control unit. So I think it is not the sensors, it is either the harness to all the sensors, the harness from sensor harness to control unit or the control unit. Is it possible to check what to expect on the wire positions in the plug of the harness? Does anybody have a pin out, maybe I can easily check the harness?

[Schorly]

I found the supply voltage and ground. As I have easiest access to the two outermost sensors and the left hand one made the ticking noise and the right hand one does not, I concentrate on them. On both I can get the supply voltage, which is between the two outermost pins. In the middle is the return signal and on bot I get continuity between the sensor end and the plug between the two harnesses. So they both get power but one is making the sensor tick and the other doesn't . This really puzzles me. Nobody out there who can help and has an idea?

[Schorly]

Went to work, stopped at the petrol station, put the cart in to reverse and I get the normal short sound from the parking sensor module. Went around the car and it looks like they all now work again??? Now I ma totally confused.