Mudboi222

Hey guys im wondering if anyone could tell me where i could find the TCU & the TCU fuse location. Im having to replace the transmission in my 89 Jeep Cherokee Laredo 4x4 and before the transmission went out i always had to shift my gears manually and ive been reading and have come to believe its most likely my TCU so i figured while i wait to find a new transmission ill go ahead and mess around with my TCU and check it and possibly change it. So im wanting to start at finding its location and the fuse to it?

cruiser54

Up under the passenger side dash right below that diddy box under the glove box. Fuse is close to the TCU in the harness usually wrapped in yellow tape.

cruiser54

Photo of a TCU on the bench

Mudboi222

Thanks man. Really appreciate it, Btw how do you have the voltage meter hooked up? Does my jeep have to be running for me to tell if my TCU is working right?

cruiser54

That photo was taken just to illustrate "back probing" with meter leads.

Check that fuse absolutely first. Another area that can give you issues with your tCU is below, with a photo.



Cruiser’s Trans Plug Refreshing

Over near the transmission dipstick tube are 2 rather large connectors. One is black and the other gray. These 2 connectors carry all the info between TPS, TCU, NSS, speed sensor, and transmission solenoids.
Unplug each one, visually inspect for corrosion or bent pins, spray them out with electrical contact cleaner and plug them back in.
　
Additionally, if your Jeep is an 87 to 90 Renix, it’s always a good idea to reach up under the glovebox area and unplug the connector to the TCU and spray it out along with the receptacle of the TCU. While you’re there, find the fuse right in that area for the TCU. Remove it and spray out it’s receptacle and clean any corrosion from the fuse.
Revised 9-10-2012

Mudboi222

Thanks man, i found everything to the TCU. I checked my TCU and it dont have dust or anything on it, the wires are nice and clean but i checked the fuse and its blown. It has a 10 fuse in it. Is that the one i should replace it with?

cruiser54

Yup. Go for it.

Mudboi222

Well i got my new transmission in finally, Threw it in drive hoping for some luck after i put the new fuse in it and it still wont go. What do you recommend i do now?

DFlintstone

Wont go at all? Pardon these questions...It has fluid, the drive line is in, and you have the converter to torque plate bolts in? Oh...and the transfer case...is not in neutral or otherwise helping it "not go at all".

Mudboi222

Oh wow my bad. I was typing to fast and didnt pay attention to what i was saying lol. In my jeep ive always had to manually shift it even before i put the new transmission in it. Im trying to figure out why. I checked my TCU and the fuse was blown. So i replaced the fuse hoping it would shift on its own when i put it in drive. Still a no go.

richamor

sounds like it may be a tps issue. I've read where several folks on here have fixed their transmission by cleaning or replacing the tps.

cruiser54

TPS will affect SHIFTING. Won't keep the Jeep from moving.

Mudboi222

Yeah i know that. My jeep does move but i have to manually shift gears and its so annoying. It did the same thing on my old transmission so im pretty sure its something not transmission wise.

EDIT: richamor, Ill check into that man. Thanks.

DFlintstone

Ah...I found in post #1 you have an 89. (it's easier for us if you fill out your info). The 89 TPS can be adjusted, (and checked). Mine just went out in my 90, (the trans side), and it would still up-shift...not always correctly, and it wouldn't down shift with the pedal. In the link in Cruiser's (or my) signature there is a process for checking it, something to handle anyway. Your AW4 has 3 solenoids in it, two for shifting and one to lock the TC, mostly controlled by the TCU. That's about all I know...I'd rule out the wiring and the TPS, then maybe suspect a solonoid or the TCU?

Mudboi222

One of my buddies have a 88 Cherokee Limited. He just had some similar problems but his was the Neutral switch. Im gonna ask him if i can take his TCU out and plug it into mine so that i can see if thats the problem. Even if its not then i can get that out of the way. Would his work? Its a 88 Cherokee Limited. Also another buddy of mine has a 86 or 87 with the 2.5 V6 in it. Would his TCU work? His jeep has been sitting for a year bc we sunk it in a pond lol but i remember his shifted fine.