trans works normal when TCU unplugged

So i have a 1996 xj 4.0 with the aw4 trans and a 3inch lift. I've been having trans problems above 45 mph when it gets stuck in overdrive but lately its been doing it when it shifts into second gear. I did some searching and somebody said unplug the TCU and if it works normal its a electrical problem. I replaced the shift solenoids in the trans pan about a year ago because it wouldnt shift out of first gear or when it did it got stuck in overdrive. After i did it it shifted normal but it still got stuck in overdrive. I also replaced the TPS last week hoping it would be it but it wasnt. what else could it be? also will it do more damage driving around with the tcu unplugged?

If you unplug the TCU and everything works normally, it's a TCU problem.

Also, the AW4 should normally shift into 2nd gear at something like 3500-4000RPM with the TCU unplugged.

It could be anything electrical if it works with the TCU unplugged.

Have you tried measuring the solenoid resistance from ground to the solenoid drive wires in the connector at the TCU? If you do not get 11 to 15 ohms or so, move one connector closer and measure again. You should check next at the bulkhead connector behind the fuse panel (accessible from the engine compartment, it's somewhat of a bear to get at) then the connector by the dipstick tube for the tranny harness. When your value changes, you know the problem is between the connector you just checked and the connector you last checked.

Also try adjusting the TV cable, it may not be allowing enough pressure into the valve body (I think, might be using the wrong terms) to actually shift the tranny even when the solenoids are working right.

kastein said:

It could be anything electrical if it works with the TCU unplugged.

Have you tried measuring the solenoid resistance from ground to the solenoid drive wires in the connector at the TCU? If you do not get 11 to 15 ohms or so, move one connector closer and measure again. You should check next at the bulkhead connector behind the fuse panel (accessible from the engine compartment, it's somewhat of a bear to get at) then the connector by the dipstick tube for the tranny harness. When your value changes, you know the problem is between the connector you just checked and the connector you last checked.

Also try adjusting the TV cable, it may not be allowing enough pressure into the valve body (I think, might be using the wrong terms) to actually shift the tranny even when the solenoids are working right.

Click to expand...

I haven't tried measuring the resistance yet becuase my ohm meter decided to break on me. Do i check with the connector plugged in or unplugged? I did try to adjust the TV cable but that didnt do anything. The last time i tried that it would pull out for the last 1/4 inch but now it doesn't? I dont know why that would be like that but i dont know if its related or not because the last time i tried to adjust it the trans would get stuck in overdrive still

You should check with it unplugged. Try lubricating the ratchet mechanism a bit and readjust again maybe?

Ok thanks im about to get a new meter now then ill check it and post up what ohms i measure. Do you know which are the drive wires by chance? I'll do some searching on it when i get back if not.

Not sure, if you have or can get a factory service manual, it'll have the pinouts for each connector in section 8W somewhere.

You've got a 96 actually... I have the manual for that year at home. PM me later tonight if you haven't figured it out and I'll get you the wire colors for the correct pins at each of the 3 connectors I mentioned. Might be busy, so I may not respond till later tonight or sometime tomorrow, but I'll try and remember.

I have a haynes manual and just looked through it but couldnt find anything. So if you can check for me it would be greatly appreciated. thanks for your time and no problem if it takes you until tomorrow to find out for me.

The Haynes is useful when you want some good info, some blatantly misleading wrong info, and a few unrelated pics :doh: It is fairly accurate for the front lighting harness but it's hit and miss for the rest. I still have one around that makes a fairly good beer coaster.

bigalpha said:

If you unplug the TCU and everything works normally, it's a TCU problem.

Also, the AW4 should normally shift into 2nd gear at something like 3500-4000RPM with the TCU unplugged.

Click to expand...

Little different view of things:

With the TCU unplugged you will have 1st in 1-2; 3rd in 3; 4th in D; reverse, neutral, and park. If you have that, then the hydraulics/mechanical aspects of the transmission are good. That means the possible culprits are TPS, throttle pressure cable adjustment, TCU fuse, TCU, solenoids, wiring harness.

Also, the "normal" shift point for 1st to 2nd is around 4000-4500 rpm, and it won't shift with the TCU disconnected.

"D" (Drive)................ Sol. 1.............. Sol. 2
1st Gear .................. ON .................. .. OFF
2nd Gear ................. ON ...................... ON
3rd Gear .................. OFF ..................... ON
4th Gear .................. OFF .................... OFF

"3"
1st Gear ................... ON ..................... OFF
2nd Gear .................. ON ...................... ON
3rd Gear .................. OFF ...................... ON

"1-2"
1st Gear ................... ON ..................... OFF
2nd Gear .................. ON ...................... ON

"R" (Reverse) ............ ON ..................... OFF

"N" Or "P" ................. ON ..................... OFF

Ok my 89 4.0 aw4 is having a similar problem, so I'm going to try to unplug the tcu.. only thing is I don't know where it is haha.. can someone point me in the right direction please. Haynes was no help for me on this issue either.

Up under the glovebox, right above where the passenger's feet would sit on the floor.