I have/had a similar problem with air suspension light coming on when all appeared normal. Turn off and restart and it would be gone. However the problem got worse and restarting had no effect. As the problem started as occasional and progressed to all the time I decided that it was probably mechanical.
Yesterday I removed the compressor and cleaned the filter/dryer and the exhaust valve. Some of the desicante in the dryer had turned to powder and was on the wrong side of the retaining pads. The stem of the mushroom shape exhaust valve was corroded. Put back together an all operated normally.
Thinking back over the problem, I now recall that the vehicale had stop "farting" and only made a slight hissing sound (sometimes) on unlocking and opening a door. Could it be that a lack of "farting" noise is an indication of a blocked dryer or stuck valve? I intend to replace the dryer as I think the problem will return.
IvanR
2005 D3

