Suspension Rising and Falling by Itself
 

Was asked by a friend to check out his A8 as the air suspension is acting weird recently. For some reason, the ride height is rising and falling constantly, with the consequence being that the compressor is running every 30 seconds or so. The symptoms are very clear. Once the car is started, the suspension will either rise or fall by about 15mm. When it rises to it's maximum, the compressor will stop and the car will drop by about 15mm. The compressor will then start again and the sequence will keep repeating.

There are no leaks as the car doesn't lose any air overnight. Not only that, but there is not even a single error code in module 34. Whilst it was running, I checked several measuring blocks to see what was happening. Group 007 shows the values for 'Transverse lock-up (air spring valve status)', and during one half of the rising and falling, the two values for the front axle show ON whilst the other two show OFF, the rest of the time they all show OFF. Group 004 also seems to confirm that all the level sensors are functioning properly as their values increase and decrease, and changing the MMI setting from Comfort to Lift shows a marked difference in all four values.

Reading through the SSP 292 (in the D3 Tech Dump), I'm suspecting that it may be the G291 sensor in the valve block being the culprit, as the pressure reduction procedure vents air through an exhaust solenoid. However, since there are no fault codes specifically pointing to the valve block, I'm not 100% if this is the case, and can't think of anything else in the system to check.

Unfortunately, I only took one photo of the measuring block screen.

http://forum.a8parts.co.uk/attachmen...1&d=1616442512

I would think it's got to be valve block related if the whole car drops and not just one corner. I was thinking perhaps the air tanks but again wouldn't expect all 4 to drop.

A calibration may sort it. Height sensors should show an error so don't think it's that either.

A full calibration had been done on the car, with no effect.

I was hoping to find at least one error somewhere in the system, but nothing at all. I did come across something earlier today but need to get some more history on the car before proceeding.