98 Jeep Wrangler check engine light....?

[VeronicaK]

continues to come on and the diagnostic test at Auto Zone said that an error has occurred due to the gas cap being left off. the only problem is that the gas cap is on so the diagnostic test is wrong. what is really causing the check engine light to come on??
this is a new gas cap. how is the pressure sensed?

 

[Silverstang]

If that is the case
then the gas cap is not sealing, or holding pressure like it should. So unfortunately it would need to be replaced.

 

[Noah'sArk]

I've had the same thing happen to mine with a new gas cap and so has my cousin who owns an 05 wrangler .... If your original cap is gone you will need to replace it with an oem original ... I'm not quite sure how it senses the loss of pressure but it does .... If it continues after this disconnect your battery to reset .... You could also get one from your local junkyard cheep.... I have the same Jeep as you... Auto zone is fairly accurate when testing your codes

 

[kittkatt]

I took my jeep to advanced auto parts and i'll just tell you this; most of the people that work their know nothing when it comes to vehicles and parts.I had a battery replaced once and the guy broke the bolt when replacing the battery and rather than fixing it like he should he just told me to get my husband to put one on.
Many times O riellys have given wrong parts. Had a diagostic test ran once and it read somthing completely different. What i would do is call the dealer or any good reliable mechanic and tell him what is going on and ask what could be causing that. I would still mention what the dianostic test read, that way they will have somthing to go on. Most of the time they can tell you without charging you. Call as many mechanics as you can. You can also go and buy another gas cap to see if that is what could be the problem, just keep your receipt just in case it isn't, that way you can return it.
Just make sure you don't buy the same gas cap as before. Buy one that's different.
Hope this helps.