Ford Repair: 1991 Ford Explorer Check Engine, ford explorer sport, oxygen sensors

Question
I have a 1991 Ford Explorer Sport. I noticed a week ago that the "check engine" light would come on after about 15 minutes of highway driving. The first time I pulled into a gas station and turned the engine off for a few minutes and it stayed off when I turned the engine back on. The light came on again after about another 10 mintues on the highway. It would not happen while I was driving around town.

I brought it into the dealer they ran a diagnositic and told me the oxygen sensor needed to be replaced. I had them replace the part. When I got on the highway this AM the light came on again as before (after about 15 minutes). Can you think of any possible causes?

It seems like this started after I had the state inspection done. Could the emissions testing have done anything?

Thanks

Joe


Answer
The "Check Engine" light comes on when an engine sensor goes out of its normal operating range.  It is common when an Oxygen Sensor starts going bad, for the "Check Engine" light to go on-and-off depending on driving conditions.  I would take the vehicle back to where you had the repairs done for further disgnosis.  No, the emissions test couldn't cause any problem.  I would guess that one of the Oxygen Sensors is still bad.

I hope this helps,
Dave