AW4 stuck in gear when engine hot?

96 Country edition.
Last week the AW4 was stuck in third gear so I did this http://www.transonline.com/transdigest/magazines/1997-10/Shift%20Pointers/index.html and found that I had a bad solenoid. I pulled the pan and the solenoids and hot wired them to 12V and found that the one closest to the rear of the jeep was bad. So, I replaced it. I thought everything was good to go until the engine got hot (its running at about 220 degrees which is 30 degrees warmer than it did a few weeks ago, I have no idea why). The engine and trans usually get warm when I am in third and thats where it gets stuck, but today I stopped for some fuel after it got stuck in third. When I started it back up it was stuck in first gear all the way home (10 miles). I am confused on this one. I think I am going to hardwire solenoid one and two to switches and turn them on manually to see if the TCU is bad.
1 on is first gear
1 and 2 on is second gear
2 on is third gear
Has anyone experienced this or could point me in a better direction?

the radiator is also the trans cooler, so your trans may be overheating causing the rise in engine temp or the engine is getting hot causing the trans to get too hot.

the trans fluid and coolant dont mix, but it would seem the radiator could be a the problem.

Unplug the TCU and see if you can shift it manually.

ok, it has a new radiator via the guy I bought the jeep from, I think its about 8 months old. what could cause the trans to overheat?

I will unplug the TCU this afternoon on my way home from work and see if that works, if it does shift I assume the TCU is toast?

kingmeirl said:

ok, it has a new radiator via the guy I bought the jeep from, I think its about 8 months old. what could cause the trans to overheat?

I will unplug the TCU this afternoon on my way home from work and see if that works, if it does shift I assume the TCU is toast?

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if you can manually shift through the gears without issues, then the problem is most likely an electronics issue. so it could be the tcu.

I unplugged the TCU before leaving work, and I could manually shift through every gear! Must be an electrical gremlin. Also, the temp went down 20 degrees. I kinda like driving around with the manual shifting. thanks for the help! this weekend I will run toggles to my solenoids to lock 1st and second.

when the transmission overheats it goes into shut down mode. It won't shift unless you let it cool down. If it happens again let it cool down then start it back up and put it in gear. If it is the temperature causing the problem then it will shift normally after it cools down.

You should probably get a transmission cooler if you're overheating it too much. Heat will kill the AW4 QUICK.

reelbigdundy87 said:

when the transmission overheats it goes into shut down mode. It won't shift unless you let it cool down. If it happens again let it cool down then start it back up and put it in gear. If it is the temperature causing the problem then it will shift normally after it cools down.

You should probably get a transmission cooler if you're overheating it too much. Heat will kill the AW4 QUICK.

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The AW4 computer has no way to determine the tranny temp, so it's not responsible. I would guess that overheating thins the fluid enough that it throws off the pressures in the valve body. Or marginal solenoids behave worse when hot.

That sounds right, I'll replace the trans cooler and then plug the TCU back in and see what happens.

on another note, what controls the overdrive in the trans? I know the solenoids control 1st 2nd and 3rd, but what engages or disengages overdrive?

kingmeirl said:

That sounds right, I'll replace the trans cooler and then plug the TCU back in and see what happens.

on another note, what controls the overdrive in the trans? I know the solenoids control 1st 2nd and 3rd, but what engages or disengages overdrive?

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The first two solenoids control the shifting. Third solenoid controls the t/c lockup.

solenoid one ON solenoid two OFF = 1st gear
solenoid one ON solenoid two ON = 2nd gear
solenoid one OFF solenoid two ON = 3rd gear
solenoid three ON = t/c engaged

so what controls fourth gear??

Just got back into town. The line you're missing is:
solenoid one OFF solenoid two OFF = 4th gear

Hence the reason why no power to the TCU gives you 4th gear with the shifter in (D).

gotcha, thanks.
I am running the jeep with the TCU unplugged.
I also ran a 12V supplied toggle switch to solenoid 1 and 2 so that I can lock in 2ND gear.