Allroad A6 Quattro '07 plate - suspension probs :-(

[covieG]

Hi all!
I have recently acquired a very nice 2007 Allroad. Lovely vehicle, good price. I now need a bit of help as I am a newbie with this sort of vehicle.
Suspension needs sorting. Diagnostic analysis suggests I need a suspension height sensor. The offside suspension sinks until it rests almost on the wheel.
Have been speaking to an "expert" who doesn't seem to have confidence in what he's saying. As someone who has no idea, this "expert" has led me to look elsewhere for advice. These are the questions he could not answer:
Is there a sensor for both offside & nearside suspension, or just one for both.
Is there a way I can determine if my problem is a sensor prob, suspension airbag prob or a pump problem?
All advice appreciated. Can't afford Audi dealerships. Have previous experience with P38s
Thank you all for any advice!

 

[Amphitryon]

Have you posted in the right forum? Wouldn't a 2007 be a C6 chassis. Anyway, for my allroad, which is a 2001 C5, there is a height sensor for each wheel so four in total.

Determining if an airbag is leaking is reasonably straightforward. Park the car and then engage jacking up mode. The purpose of that is that it stops the car from making adjustments by itself. If you don't engage jacking up mode, if one airbag leaks the control unit will lower the whole car to keep it level and then you won't know which one is leaking. With jacking up mode engaged, measure the height of each corner. Ideally, you want wheel arch to wheel centre but as there isn't a centre mark, at least not on my wheels, you could measure wheel arch to road. Then leave the car alone for a decent length of time, at least 12 hours, and then repeat the measurement. Some lowering is to be expected as the air cools but if one corner goes down dramatically then it is probably leaking.

You can do this test at any level but, because of the way the rubber folds over itself, you're more likely to see a leak at level one than at one of the higher levels. The lower the level the more rolled over the rubber is and the more likely it is to open cracks in perished rubber.

If the height is reasonably stable like that then usually the next suspect would be the compressor, especially if there is a general failure to raise to one of the higher levels. Typical symptoms are that it takes ages to raise one level or even takes so long that the system gives up and puts up the warning light on the rev counter. Usually, when that happens, turning the engine off and on again and re-selecting the "Up" button will cause it to complete the raise but when the compressor is really bad it may not even do that.

Obviously the compressor can be replaced but it is also possible to repair it. Usually it become inefficient because air leaks past the piston ring. Andy Fulton does two kits to repair this - the cheaper one contains a new PTFE piston ring and the more expensive contains a replacement cylinder too for case where the cylinder is badly worn or has scratch marks in it. See https://www.ebay.co.uk/usr/bagpipingandy?_trksid=p2047675.l2559 and http://www.bagpipingandy.com/ Andy is also an expert on this suspension system.

I have no experience of other problems with this suspension, i.e. sensor, control unit or valve block failure. Reading a long thread over on http://www.vwaudiforum.co.uk/ these seem a lot less common than air bag or compressor problems. If you're still puzzled after trying the height test then try e-mailing Andy.