Not your usual parking sensor problem...

[neckarsulm]

The rear parking sensors on my friend's RS6 are playing up.
I've seen them before when one is faulty and it logs a fault code and system does a high pitched beep and then shuts off.
However this time there are no fault codes, system thinks all is normal but it's not.
What is happending that one or two sensors are registering something is close to the car when it's not.
They are the two middle sensors.
With Vag Com you can see what the sensors are measuring and the outer 2 are on 255mm (i.e nothing close), the inners are between 60 and 80mm.
Also sometimes the outer sensors don't seem to pick up when I have my hand over them
I took bumper off to swap the sensors around and I was disappointed to find that the fault didn't move with the sensor so it's either loom or control unit.
Anyone seen this before?
Thanks

[Shoppinit]

I've seen this when the sensor picks up the number plate holder. They have an unbelievable field of view - close to 180 degrees - and the edges of the number plate not being quite flush was enough to set the sensors off.

[neckarsulm]

I remember Evo had that issue with their B7 RS4.
However with the bumper off and sensor sat on top of bumper bar they still do it - or even hanging off and pointing downwards.
Going to order a second hand module I think, can always stick it back on Ebay..

[Shoppinit]

There's only one control module. I wonder if you can swap the front and rear harness connectors on the module to see if the problem moves.

Keep us up to date. It's an odd one.

[chunky79]

Sounds like a module fault. Defo not sensor fault and very much doubt loom fault that you have described.

[neckarsulm]

The front and rear sensor plugs on module are different (prob just as well as imagine the confusion/damage it could cause if incorrectly connected!)

Got a module off Ebay from a chap in Scotland, £30 delivered and he even messaged me to say it was out 1st class soon after buying it

Will report back

[neckarsulm]

OK, tried new control module but no difference.

So set up VCDS on the folded down back seat so I could get a bit more scientific and see what each sensor was doing without having to move away and concluded all 4 were shot.

Ordered 4 from TPS and it was only with all 4 swapped that it worked correctly, hence why moving them around didn't make any difference.

I have a suspicion the sensors don't working 100% independently but in left and right pairs and a calculation based upon this is in measuring block 3 called 'calculated distance

If the issue had been dealt with when the problem started it would have been a lot easier to diagnose but I now know they'd be playing up for ages and were all the original sensors marked 2003.

[chunky79]

That is very unlucky, and also strange.

[AdamB]

Hi, I've got similar problem with my S6/C5.... middle/right sensor has always looked cloudy but worked fine, and since it sat for 2 weeks at the dealers while I was on hols, I usually get solid beeping sound when reversing... but then it will clear and start functioning normally 1 time in 5 or 6. I suspect the 'cloudy' sensor but haven't had time/can't be arsed to sort it, though reversing an Avant on a dark night with full-tint privacy windows is 'interesting' (OK, I bottle it and hop out 2 or 3 times to check like a gurl! lol)

[tmg]

timely question

so I had something similar with the mid right sensor. I swapped it out this morning (I could get at it without taking off the bumper (woohoo)

When I had it out, it was obvious that one of the three wires had corroded through and contact was intermittent (sometimes beeped and sensors didnt work, sometimes it worked fine). the plastic connector was also a bit broken, which is probably why there was corrosion, and I broke it open a bit further to get some pics. the wire with the green deposits was the one that was broken.

pics below

and

so a quick swap later, all was well.

t.

[chunky79]

How the hell did you do that without removing the bumper? You got ickle hands?

[tmg]

gorilla paws actually - but there was loads of room - got both hands in there to get the sensor disconnected. Will take a photo later, but no access issues at all

(that said I do have the factory towbar so it may be somewhat different)

t.