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4.0L, 42RE, 242...

This damn thing wont shift out of first gear. It was driving fine. I stopped at a traffic light. When I went to take off, it wouldn't shift out of 1st. Running it to about 3000 rpm, and then tossing it in neutral for a second, and then back into gear sometimes triggers the tranny to shift up.

Plugged in my SnapOn MT2500 scanner and it told me it was requesting Gov pressure, but not seeing gov pressure. Tossing it in Neutral and back into drive will show a rise in pressure, but not too high... maybe 5-10 psi when it is requesting 35-45.

Dropped pan, replaced gov solenoid and pressure sensor. Still nothing. Still wont shift out of 1st.

Found a small piece of snap ring in the pan. Maybe 1/2" long. Was told it was common to find that and not to worry.

Reading the scanner, it shows when you let off the throttle, the tranny will shift into 2nd, and sometimes even 3rd or 4th. Pressing down on the throttle causes the tranny to shift back to 1st.

When the scanner says that the tranny is in 2nd, you can pull the shifter back to "1" and the tranny will downshift.

Disconnecting the tranny harness and test driving. When done, and then put into "D", the engine will die a 1/2 second later. Pulling the shifter all the way back to "1" will yield 1st gear take offs.
 

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might check your input and output speeds sensors on your transmition. it is a common issue for these to fail... also when the fail they have random issues. my speed sensors failed and it wouldnt shift properly and wouldnt go into overdrive.... you can get them both from jeep they are the same part number shouldnt be anymore than $90 for both.... and they are easy to install... one bolt each ... hope that helps
 

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I am little confused here....has it failed in range for 1st or 2nd gear? If it has failed in range in 2nd and you can manually engage 1st I would check trans relay. It carries power for Gov pressure sol, TCC and OD solenoids. It should have stored a DTC for those ckts. When switched battery power is lost the REs will default to 2nd gear.
 
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