Just returned from my dealer for the famous "Check Engine Light" problem with my 2006 Wrangler X Although I had tightened and untightened my Fuel Cap several times , it didn't clear the light.
Dealer replaced cap with a new one and put the light out.
(still under warrantee)
The new cap has a printed warning that a loose cap can cause the light to go on.
Would be nice is the computer code would be able to be displayed on the odometer as it use to be on jeeps and other vehicles.