On a recent long range trip, at about 700 miles, CEL came on and remained on through the remainder of the trip and for several days after returning home. Same thing happened on a long range trip a year ago. I had planned to stop by an auto parts store to have them hook up the code diagnosis equipment but the third day after returning home, the light went off, just as it did the first time. After the light came on, I had to stop for gas at least twice and made sure the gas tank cap was on tightly...am certain it wasn't that but am at a loss to explain why this only occurs on long trips and then lingers for several days before going off. Anyone else have this problem?

 

David Copperfield is the person to blame.
Actually, you still can read some pending codes.

 

And my bet is P0171 error pending. Likely gas cap.

I have had exact same issue when descending in altitude and light goes off after I stop and start up again (usually at a gas station).

 

LEXMEX...trip was from central Georgia to Baltimore..not much change in altitude. Got gas in Baltimore upon arrival and car sat in hotel garage overnight. CEL was still on the next day (next several days actually) despite several fill-ups on the way home.

 

Well, I can tell you I also got this when I was driving down from DC to Mexico back in 2002 right as I was going through Houston. Also suspected a gas cap at the time, but after we stopped and started again no issue. Could have just even been some temporary air/fuel ratio out of order.