"Check Engine" lamp on!! Help

Ok I just bought my 1999 Merc. C280 and for the first week I had it a "check engine" lamp came on. I took it back to get service, when I got my car back it seem fine. Then a day later it came back on. Well my car seems to be running fine. But the light is still on. What could it be? I only have 53400 miles on it. It didn't do that when I bought the car. And I've already sign papers and I'm worried that I just made a huge mistake. Other than that the car is awsome. Help..

AutoZone will read the codes and give you a print out for free, if you have one near you.  Get the codes read and then go from there.

Hey thanks a lot. I really appriciate the reply. Thanks.

This will really help.