Check engine light

1999 Jeep Grand Cherokee 4.0.
Check engine light will not go out.
Took to Autozone , Orileys ,and Jeep Dealer.
No codes found.
Replaced cooling fan relay, when light first came on.
Everything works fine now.
Have tried myself to shut light off, disconnect batt. cables 10 min, 30 min.
and other methods, no luck , still, on ?
I have even traced the cooling fan relay wire to PCM, all OK.
Any help. Thanks.

I doubt it will work, but you could make it throw a code so there is something to delete. Unplug an O2 sensor, MAS, TPS, etc. Have it read and deleted. In all reality I'm guessing your PCM (ECU, or whatever you want to call it) has a problem.

When you disconnected the battery, did you hold the positive and negative cable ends together for a few seconds? The PCM has its own battery, and holding them together drains it for what I call a "full reset".

Check engine lights are fairly complex, but simple in how the operate and also must check the O2 sensor because may be sensor is creating problem that's why engine light is not working properly..