AW4 doesn't engage in 4th today

Was working fine this morning but this afternoon I drove it home, parked it for 30 minutes or so and then the Jeep would shift into 4th but it would act like it was in neutral. The engine would just rev up without actually feeling like I was in gear.

Reverse, park, 1/2 & 3 work just fine. Even when it's in D the jeep still accelerates like normal until it's ready to go into 4th and then it just acts like it's in neutral.

2000 XJ AW4. It's got 130k miles on it but the transmission fluid is topped off and it doesn't smell burnt.

Not sure what else to look at and forum searching for that hasn't yielded anything that I can find for suggestions.

It's pretty hot here today but I've got an offroading trip planned for Friday thats 5 hours away I'd like to not miss. Sad Jeeper:bawl:

I've got a transmission temp gauge installed too and it's showing normal driving temps, nothing too hot.

Might be a solenoid issue.

Article on the AW4 here: http://www.transonline.com/transdigest/magazines/1997-10/Shift Pointers/index.html

Write up on solenoid replacement: http://www.naxja.org/forum/showthread.php?t=987463

Pull the codes and see what's stored.

No CEL's yet. Just didn't engage when it switched into 4th. I drained about 4qts and topped it back off after letting it cool down and now it's acting normally again. Not sure if it wasn't the 100 degree heat today. I'll have to see what happens tomorrow

Not all codes give you a CEL--get the codes read.