Check engine light is on

Could be a faulty or loose gas cap if the vehicle seems to be running correctly. Esp if you just filled up before the light came on. That would def be my guess if the car were newer but with its age and mileage it could be a number of things. I suggest you have the codes read somewhere.

I had the same problem...............it was the MAF Motor Air Flow......if you buy the part at AutoZone for $150 you can replace it yourself (5 minutes max). If not a mechanic can do it for $500+++

may be your car has the obd2 trouble code table, you need to diagnose the code first, and I know this tool can do your car, http://chinasinoy.com/wholesale/mb-star-c3-pro-with-seven-cable-for-benz-truck-and-cars-fit-all-computer.html or you need take your car to local dealer to do it.

It may be the sensor sending unit. We were getting false readings and finally the dealer diagnosed the problem and replaced the unit at no charge. We were out of warrenty...gotta love that!

pull the fault code and look it up , erase it and drive the car to see if it comes back, generic obd2 tool isnt much money and less than guessing , that can get very pricey the code for a loose or bad fuel cap is described as a small emission leak