Jeep 4.0 Automatic not changing gears.

[75sv1]

Try unplugging the TCU. Then shift manually. It will not have kick down. You will need to slow down to down shift. I've always unplugged the TCU and left the fuses intact. If it doesn't work, then I'd say something mechanically wrong with the trans. Check the fluid with the engine not running. It should be up on the 'Z' bends. The start the engine. The fluid level should drop. See if it is down in the 'fill' range. If this doesn't happen, then probably the pump in the trans is not working. 

[Gradinen]

Update! 
I unplugged the TCU as many of you recomended, it was one 7.5 amp fuse in the fusebox and a 10 amp in the wire to the TCU. 
The car has been standing for about 18 years so I'll do some electrical contact spray in the connectors and whatnot. 
And try to meassure the TCU to see if it has volts. 

 

Thanks you all! This forum is amazing for new Jeepers like myself. 

[llhat]

7 hours ago, Gradinen said:

And try to meassure the TCU to see if it has volts. 

read in the link I provided,  there are some diagrams in the attachments and some tips from Ohm on some of the pin-out voltages, connections. 

 

 

[Gradinen]

On 4/22/2026 at 3:35 AM, llhat said:

read in the link I provided,  there are some diagrams in the attachments and some tips from Ohm on some of the pin-out voltages, connections. 

 

 

Thanks! I sure will do! One more time. Hehe.