Well A couple of days ago my check engine light came on. I read in the manual about all the differents reasons it might do this but none seem to fit, and it hasn't gone off yet. The truck has been running perfectly also, I have been watching all of the fluid levels and temps very closely and nothing is out of the norm. I had a `91 CHerokee that had an emisions sensor that make the maintainence required light come on after a certain amount of miles. Do our Expeds have the same? I have close to 80k on it

 

With my truck it was a bad oxygen sensor. The parts cost less than hooking it up to the diagnostic computer. I am going to have to buy one of those soon.

 

There are way to many sensors the drive "check engine" lights. My 2K Expy had a "check engine" and they replaced the purge valve cannister. That turned it off. Then it came on again a week later. They replaced the gas cap! It's been fine since.

 

I had the check engine light come on, and they replaced my gas cap at a cost of 45.00 later I found out there was nothing wrong with gas cap. They reset the light and boom no more problems. The real issue was after having my son put gas in the car he left the cap half secured and the check engine light will come on under those circumstances.
I recommend check all fluid levels, transmission, power-steering, brake fluid and then disconnect the battery and leave it off for ten minuets and reconnect. If the light stays off oh well, if the light comes back on you will need someone to perform a diagnostic check.

 

The gas cap is a biggy. It's a pressurized system so if the pressure isn't there, anoying light. If that seems to be it, reset the computer (disconnect and reconnect the negitive battery cable) and see if it comes back on. If there's a problem, it'll be back on.