Help, rear PDC woes

Clackers

Member
Wales
I have rear pdc on my project lockdown, and I get the long continual beep when I put it in to reverse, but that obviously means it isn't working...
I have done the old 'listen to the sensors for the one that isn't clicking' and all of them click...VCDS states left rear open or short to plus....
Any ideas folks? I'd love to sort this problem on it, to solve yet another nit picky thing out!
 
Why not swap left rear for right rear and see if the reported VCDS fault moves, if it does replace right rear :)
 
That was my next plan...see if it follows the sensor not the location.
Sods law it's the corner one and not the centre ones...a bit more difficult to get to, unless you have tiny arms and hands!!!!
 
I have rear pdc on my project lockdown, and I get the long continual beep when I put it in to reverse, but that obviously means it isn't working...
I have done the old 'listen to the sensors for the one that isn't clicking' and all of them click...VCDS states left rear open or short to plus....
Any ideas folks? I'd love to sort this problem on it, to solve yet another nit picky thing out!
I had exactly the same problem on my own car last week (the "Squeal of Doom")!

If VCDS shows the sensor as open circuit, then it is dead and needs replacing.
It seems that the original part number 4B0919275A is no longer available, but I used the 7M3919275A which is freely available as a genuine VW part. I got mine from here:

Genuine VW Audi Parking Sensors
 
That was my next plan...see if it follows the sensor not the location.
Sods law it's the corner one and not the centre ones...a bit more difficult to get to, unless you have tiny arms and hands!!!!
I have been lead to understand that the outer ones can be accessed by removing the rear wheel arch liner and going in that way. I hope that is the case, and I will be finding out in the next couple of days.

My right outer sensor is not open circuit, but is unresponsive and produces no fault codes and doesn't detect anything in proximity to it. I spotted this whilst checking mine with VCDS after replacing the dead one. If you go to VCDS Measuring Blocks for Park-Assist (76), Block 1 shows the distance from each sensor to any object within detection range. You can then stand to the side of the car and put your hand near each of the sensors in turn, and you should get a plausible reading.

If you then look at Block 4 as well, it gives the oscillation time of each of the sensors. This doesn't change as any object comes into detection range, and should be just over one millisecond. Both my dud sensors were showing over four milliseconds. I'll try and get a screenshot of the relevant VCDS screens later for you all.
 
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I have been lead to understand that the outer ones can be accessed by removing the rear wheel arch liner and going in that way. I hope that is the case, and I will be finding out in the next couple of days.
Hello Mark,

Great information, please do report back your findings about access to the outer most PDC Sensors via wheel arch liner removal. I know the 2 central PDC Sensors can be easily accessed from above with the mat black trim removed.

Thanks again for sharing great information as I’m sure one of the Azure Blue outer PDC Sensors needs replacing.

Kind regards,

Tom
 
Here we go! Nothing in range of the sensors, but the oscillation time is wrong for the right-hand outer sensor. It is dead, but not causing a fault code:

Screenshot 2023-10-02 154019.png


The original failed (Rear Left Centre) sensor that caused the open circuit fault code was also showing an oscillation time of 4.05 ms

Please note that these readings only make sense when the car is in reverse gear. If it is not in reverse gear, then all oscillation times will be 4.05 ms.
 
Here we go! Nothing in range of the sensors, but the oscillation time is wrong for the right-hand outer sensor. It is dead, but not causing a fault code:

View attachment 113884

The original failed (Rear Left Centre) sensor that caused the open circuit fault code was also showing an oscillation time of 4.05 ms

Please note that these readings only make sense when the car is in reverse gear. If it is not in reverse gear, then all oscillation times will be 4.05 ms.
I'm guessing that the right hand outer is not short circuit, just dead, so the controller sees it as OK, normal input impedance. So no DTC.
Mac.
 
I'm guessing that the right hand outer is not short circuit, just dead, so the controller sees it as OK, normal input impedance. So no DTC.
Mac.
Exactly so!

If I backed it up to a wall with the VCDS measuring blocks as shown above, the three other sensors would show the correct distance. The dud one would stay at 255cm.
 
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