What is up with A4 check engine lights?

[john at westcoastgarage.net]

You asked: "I have been in the market for a 96-99 2.8L A4 for the past few 
weeks. Have
called quite a few of the ads in my area (seattle) and it seems like every
other car has a check engine light that will not go away. WTF is up with
that? "

You have to understand that CELs don't "go away" until you actually FIX the 
problem.  You can't just turn the light off.  To do that, you need to know 
what codes are set (especially which ones are set that turn the light on), 
and then you need to effect the necessary repairs.  On cars like the A4, 
many times it's something like a broken vacuum line or an aged O2 sensor. 
The majority of fixes are simple and inexpensive, some are not.  Often a 
simple failure will set a code for something far more complicated and 
expensive.  I've seen Golf/Jettas with new secondary air pumps and diverter 
valves, at a cost of hundreds of dollars, that could have been repaired with 
8 bucks (retail) worth of good German vacuum hose.  I know because that's 
how I fixed 'em.  John