[200q20v] Help needed with a 1992 S4 Avant

[Mihnea Cotet]

Listers,

One of my friend's cars is showing signs of limp home mode or no boost...I
suspect the WG FV or the diaphragm to be torn...
We'll try to pull the codes this evening but the problem is that the "Check
engine" doesn't seem to light (the oil pressure warning light doesn't light
either and the Autocheck seems to have been somewhat disabled but it's not
the fuse)...how are we supposed to pull the codes if the check engine light
doesn't work? Does the LED procedure for a 200q20v work (SJM doesn't
mention anything like this on his web site)

FIY, the car isn't chipped and started to do like this when he installed a
K&N cone airfilter (I know he shouldn't have but oh well, it's his car, not
mine)

Thanks a bunch in advance,

Mihnea