william91xj

Still can't figure out why my transmission wont shift on its own. Tried changing the tcu today and didn't do any good and the inline fuse is good. Do u think that its the solenoids in the pan or am I missing something? Wiring looks good to.

Jesse Hallum

A dirty/malfunctioning NSS or TPS can cause this. Codes?

Radi

Try measuring the solenoid resistance. You can do it from the transmission harness where it plugs into the TCU. Should be in the 12 ohm ballpark.
Might also measure the voltage there by backprobing the connector while driving to see if the TCU is attempting to operate the solenoids.
NSS shouldn't be an issue on a '91, at least not where it would completely prevent shifts, but the TPS might be.

Anything in particular happen right before it stopped shifting?

william91xj

It was like that that when I got it but didn't know the the Tps would keep it from shifting. I will start checking all the the wires I guess. What would the Tps read if its good or bad?

william91xj

Do I check all the wires in the tcu

Nick-B

Always do the easy stuff first.
Did you adjust the TV cable?
https://www.cherokeeforum.com/f2/free-quick-fix-41821/

william91xj

Whould that keep it from shifting on its own and where and how do I do it

cruiser54

91 may still have the fuse wrapped in the yellow tape up under the passenger side dash. Check it out. If the fuse is blown or corroded, it won't shift.

william91xj

The fuse and wiring look good

cruiser54

Which fuse?

william91xj

The one taped up with the tcu

cruiser54

Did you remove it from the holder and clean it off? Check it for continuity with a meter?

william91xj

Didn't check with meter also would like to know which wires out of the tcu I need to check if u know

cruiser54

I would be sure I had power THROUGH that fuse with the key on first.

If I had power, I would make sure the TCU is plugged all the way in.

There are some connectors under the hood near the dipstick tube that carry all the info between the tCU, various sensors and trans solenoids:

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

william91xj

Ok thanks ill get back with u when I can do it