said by PoloDude:There is no way putting another 55c in the tank set off the CEL. However you should check that the gas cap is on securely.
This is what I was going to say. My mother had a 04 Ranger, and the CEL triggered, and I believe the fault was just a general emissions system code. The gas cap had a bad gasket. New cap and problem went away.
I'm weary of any mechanic that cannot (or will not) tell you what the codes are that come out of the PCM.