JRW90XJ

A few weeks ago i posted about my tranny not shifting....i was told it was 1 of 3 things....TCM fuse....bad TCM...or bad TPS....well...the fuse was fine....and i unplugged the TCM from the connector and i could shift it manually....well i took my buddies TCM out of his 89 cherokee and slapped it in mine and....still wont shift on its own...and yes his TCM if fine...so now i am left with only the TPS....my question is why would the TPS be causing my rig not to shift on its own...i mean...if the TPS was bad wouldnt the truck run like crap????.....truck runs great....just wont shift on its own????....any input will be greatly appreciated!!!!

ct67_72

vehicle speed sensor. Tps will not stop it from shifting, just effect the shift points.
do you have any codes? have you checked for codes? Other than PCM, the vehicle speed sensor is one of the only things to stop it from shifting.
The only other thing is the range sensor on the pass side of the trans. It tells the pcm which gear you selected.
Either way you should have a code, and I would not thing it would be the range switch but it is possible. Probably VSS

SeriousOffroad

The Range Select Signal goes through the NSS. Pull it, clean it, lube, reinstall.

JRW90XJ

so where exactly is the VSS im not sure where its located...tranny???...Tcase????....i crawled under there but not sure what im looking for???

JRW90XJ

sorry....to clearify...you mean pull the NSS and clean it, lube it, and reinstall????....or where you talking about the range selector???...and when you mean range signal...are you talking about tranny or tcase???

fantic238

Buy it, use it, break it, fix it,
Trash it, change it, mail - upgrade it,
Charge it, pawn it, zoom it, press it,
Snap it, work it, quick - erase it,
Write it, cut it, paste it, save it,
Load it, check it, quick - rewrite it,
Technologic..Technologic..

SeriousOffroad

Yes.

fantic238

Ok, first of all, it's a renix (TCM separate), so no codes or CEL. The vehicle speed sensor CPS (crankshaft position sensor) has nothing to do with the tranny, the transmission has it's own speed sensor in the tail housing.
The TPS (throttle position sensor) instead, is a double unit that serves both ECM and TCM, but internally there are two separate potentiometers that produce two different volt ranges. If the TPS is faulty, the transmission won't shift and stay in 1st, it will shift to 2nd but only when you reach high RPMs. The tranny computer combines the informations between output shaft speed and throttle position, to calculate instant torque, then selects the appropriate gear to move the vehicle.
My vote on the TPS.

caged

x2 on the TPS.
easy to change out and you'll be surprised at the results.

when i bought mine, it wouldn't shift. had to shift manually.
changed the TCU, replaced the blown fuse, replaced the tranny, then when i heard about the TPS, changed that, and what do you know...
been great since.