What could cause a CE light on an S320?

[Hatterasguy]

Someone I know is looking at buying a 1998 S320. The cars seems to be in pretty good shape but it has the CE light on. Now what could cause it to trip and is their anything I could check in a parking lot with basic tools? The car is on ebay and we need to know a little more before bidding.

Also what scanner is needed to read the code? I thought these cars were just OBD-2. Autozone has cleared and read codes off of my friends W210 for us. The GM dealer that has the car claims they can't read the code. Since they seem to be very honest with the rest of the car I have a feeling they havn't tried or maybe just don't know.