CEL?

I recently got my 02'E320 fixed(I needed new spark plug wires and a "major" tune up) b/c my CEL was on last Wednesday(12-5-07).It cost me roughly $800 but I was satisfied after my car was running better than when I bought it 6 months ago and very smooth like a benz is supposed to drive.Well I was out to eat and got a lil drunk so I let my girlfriend drive home and I noticed the CEL was on again when coming to a stop.I dont know how long it had been on when I seen it but I was only in the car approx 30 mins when I noticed and she said it just came on but I mentioned it first.My car is driving the same w/no apparent problems as there was before(I had a bad idle and acceleration at start up and take-off) but the CEL came back on.I have yet to have any codes read on it since it happened tonight but I will tommorow.Anybody have a clue whats wrong or how I can reset my comp and get rid of that CEL.That CEL and bad drive bothers me more than anything dealing w/cars.But to remind, my car is running fine w/no apparent problems to complain about just the CEL that I see on the dash that I want gone.Any suggestions or opinions will be greatly appreciated.Thanx.

I forgot to mention, when I noticed that the CEL was on, I noticed that the ESP light was on.I turned it off ASAP but I have never drivin w/the ESP on for longer than 10-15 secs.She prolly turned it on when trying to roll down the window, thats the only time I hit it but I catch myself everytime, I dont know how long it was on b/c she rolled the window down a couple of times.What does ESP mean? Will driving w/it on hurt the car or its drive ability? I was only in the car 30 mins but obviously I have a unwanted problem that needs fixed ASAP.

The CEL is on for a reason.
Reading the codes will determine why. You don't give vehicle mileage/history etc.

Wish i could get 800 USD for a tune up especially with the CEL still on.

Its possible that the CEL is on because it wasn't cleared when the tune up was done but I guess you will find the MAF or similar is in need of change. No big deal but this should have been identified when the "BIG TUNE UP W" was done!! The light is much more sensitive than the driver at determining when something is wrong. The system always applies the same criteria. people are all different. some are sensitive to misfire etc but others are totally blind unless the car basically stops or won't start!!

The ESP is turned OFF when the triangle is on constantly. If the triangle comes on for a second or two (with the system enabled) it shows that the ESP has had to intervene and restrict power / apply brakes to a wheel to prevent a skid. If your friend accidentally knocked the knob she basically turned the safety system OFF. If you had hit ice or needed to do a high speed avoidance manoevre you would not have had a "guardian angle" with you. It wouldn't have made the car dangerous, just you wouldn't have had the advantages of modern electronic safety systems.

Stuart

NO PROBLEMS:)
 
After about 4 drive cycles I turned my car on to leave and the CEL was off.Seeing that it wasnt on anymore was the best news I had all month.Thanx 2 all for yo input and answers.