What is up with A4 check engine lights?

[Tihol Tiholov]

The CEL (MIL more officially) is not such big a deal ... unless it drives
you up the wall.  More important is how well the car runs.  You can use CEL
on to buy it cheap and take care of it later.  One of my VAG products ('99
2.0 bug) ran perfectly (still does) with full power and unchanged fuel
economy with CEL on for tens of thousand km - reason was front OXS or MAF,
can't recall.

Once I was going to test drive a C-class MB AMG 3.6 or some such - idled
very well, then I pointed to the young salesman at the CEL staying on.  He
got scared and the drive was off.  Recently test-drove a brand new Jeep with
the CEL on the whole time, seemed to run pretty well.