Mechanics

TRANSMISSION SHIFTING

1999 Jeep Cherokee

Transmission problem
1999 Jeep Cherokee 6 cyl Four Wheel Drive Automatic 95450 miles

WE just bought this jeep from our son and we are the third owners. It was very well taken care of and is for the most part, in great shape. However, the transmission will not shift from second gear to drive until the rpm is between 3000 and 3500 until warm. After it is warm it will shift at around 2800rpm.
Transmission seems to run normally except when shifting into high gear. Bought with check engine light on, changed output speed sensor on transmission and check engine light is now off. I am leary to take it to a transmission garage. I believe they would automaticllay say it needs a rebuild and I do not believe that is the case.
I do not know if the transmission fluid and filter has every been changed. Thanks for your help.
Avatar
Gene Martin
January 13, 2009.




Ok lets first start with the engine light. Do you have the code? If not and the codes were not cleared then call your local parts stores and find one that does a free scan and get the code then have them clear the codes and let me know what that code was and we will go from there. Get back to me.

Racefan966
Jan 14, 2009.
When I changed the output speed sensor on the transmission, I disconnected the battery for 30 minutes and the light went out. The code was P0720.
The actual question was about the transmission not shifting properly.

Tiny
Gene Martin
Jan 14, 2009.
Ok I ask about the codes because sometimes they can tell us something, as this one happens to pertain to your problem. A speed sensor tells the computer vehicle speed with that and other sensor inputs it determins when to shift to the next gear. There are two speed sensors an input sensor and an output sensor. Now did replacing the sensor fix your shift problem? If you shift it manually does it shift as it should? Get back to me and we will take it from there.

Racefan966
Jan 15, 2009.
I have the 42RE transmission and it only has an output sensor (no input speed sensor)and replacing it did not help the shifting problem. I have tried shifting manually; 1st gear, 2nd gear and then drive. No help. Engine still over revs before going into drive.
Through my research, I found I have the 42RE Select-trac transmission which calls for just and output speed sensor. If there is an input speed sensor, where would it be? I appreciate your patience in pursuing this problem.

Tiny
Gene Martin
Jan 15, 2009.
Ok with what I have found it sounds like it is going ot take a scanner from this point. I could be the governor solinoid or any other solinoid on in the trans that controls lock up and so on. The trans should also be checked for fluid pressure too. Has it had a trans service done any time recent?
This could also be the TPS as the PCM uses its signal to control the TCC operation (torque convertor clutch). So do you have a digital multi meter if so let me know and we will test the TPS and make sure it is working right if so then I hate to say it but it is to a shop to see what the solinoids are doing at the time of the problem. Get back to me about the multi meter.

Racefan966
Jan 16, 2009.
I do not have a multi meter. I could purchase one if neccesary.
I only drove the jeep a few times, but it appears that after a half hour or so driving around, it seems to shift normally.
When the jeep is cold, the rpm will go to 3500 rpm before shifing in drive. But as noted above, after driving awhile, it will shift at approx 2000 rpm into drive from 2nd gear.
Thanks,
Joe
AD

Tiny
Gene Martin
Jan 17, 2009.
Ok if you can get or borrow a multi meter not a realy spendy on just a basic one and test the TPS to see it is may be the cause. The black and dk green wire is the reference wire. You need to back probe it and with the key on engine off the voltage should read about.26 to.8 throttle closed. Now slowly lift the throttle the voltage should slowly and steadly increase to around 4.6 volts with no drops or glitches. Let me know what you find.

Racefan966
Jan 19, 2009.
I am in the process of getting a meter, but it may take me a few days because I am working late everynight. I will get back to you asap.
Thanks for your patience.

Tiny
Gene Martin
Jan 22, 2009.
Ok that is fine just get back to when you are ready to do a couple of tests and we will see what we can do.

Racefan966
Jan 22, 2009.
I got a meter last night, now what?
It is really something how when it is cold that the trouble is ther, but when the jeep is warmed up and driven for awhile, it shifts fine.

Tiny
Gene Martin
Jan 24, 2009.

AD