i have a 2000 caravan base with the 3.0l and the 4 speed trans.
i have been getting a p0123 code accompanied by some rough running for a couple weeks. i have picked up a tps but have yet to put it in.
yesterday the old girl went nuts. the transmission started shifting all over the place and went coming to a stop was shifting down way to early. finaly the MIL came on. i pulled the codes and in this order. p0123, p0121,p0731,p1782,p0700. i know what the codes all stand for but i am hoping it all comes back to the TPS. once the codes set it leveled off and was doing fine. this morning on the way to work it did fine and had no issues. it is worse when it gets warmer. is it possible that this is all the TPS?

 

Well, you have the codes, have you ever thought of doing a google search for the diagnostic proceedure for those codes?

I've never heard of a TPS problem causing rough running.

Sometimes people get so tunnel visioned and get a code then start attacking sensors and don't look at the basics of the mechanicals like bad valves, tune up, etc. I recently came across a 2000 caravan with a 3.0 that had a rough idle. some shop put in all kinds of new parts (distributor, dist cap, crank sensor, plugs, wires, map sensor, PCM, coolant sensor and more stuff). We discoverd the problem with running rough was a bad exhaust valve on #6. The owner was so upset that they dumped almost $1000 into trying to get it run, the gave up and dumped the van as is.

 

maybe rough running was a bad choise of words. hesitating would be a better description. the hesitation would happen upon acceleration and a drop off of power intermittantly when trying to accelerate. rich condition at idle when started and stumbling due to such. that what was followed by the P0123 code. i have worked as a mechanic (ASE certified from 1990 to 2000) and know the basic troubleshooting. the other codes came along yesterday with the plethora of issues, such as the transmission changing gears (downshifting as if i had floored the pedal), high idle, and a few other things. the transmission codes came after the P0121 had set and the transmission had done a few hard downshifts on its own. i came here to ask a question and get told i need not fixate on the codes. well i know this. i am not going to go insane chasing codes that might have been caused by another issue. this is why the question was asked. now odes anyone know if several hard downshifts while coasting could cause the P0731,P1782 and P700 codes?

 

First you don't need to be snippy with me, HTF am I suppose to know your master level. The way your question started, you came across as the average Joe trying to fix their car without taking it to someome that has your caliber of knowledge and skill. I'd think someone who's been in the field as long as you would be able to diagnose a simple poteniometer?

My senario about checking other things is to point out how one needs to use proper diagnostic procedures so they don't get caught up in throwing parts at codes.

 

part of the problem is that i checked the TPS after the P0123 code and it checked good. so did the signal voltage. two days after that it acted up again. (seems to be temperature sensitive) it only acts up when it gets warm out. the morning i checked the TPS it was in the 40's. i was wondering if anyone had run into a transmission shifting issue related to the P0121 code which showed up yesterday. i have a new TPS laying in the seat of the van but have not had the time to change it. the codes that are showing now for the trans i believe could have been caused by the strange shifting (mostly hard downshifts at 0 throttle). i was just seeing if anyone else had a similar experience.

 

From a Saturday mechanics perspective at least it looks a bit more cut and dried. You are getting two TPS codes. Only thing that can generate them as far as I know is the TPS, wiring or maybe the PCM istelf. I'm sure in the past you have tested component fuctions, found them good, yet changing them fixes the problem. I know I have. Apples and oranges but I worked avionics systems in a flight test squadron in the Air Force for many years. Had access to any test equipment you can think of and engineers who designed the systems. Inspite of all that know how backing us up, there were times when it came a point where we just had to change the most likely component. Many of those few times it would fix it. Post fix, engineers and us techs would scratch our heads for days or even weeks trying to come up with the specifics. Sometimes we did. Other times we would just chaulk it up to the wonders of electronics. If this were my van I would check wiring continuity/power, test the TPS hot and old, then change it.

TPS/transmission function? Tough nut. Couldn't find a smoking gun that links them other than possibly a kick down function at WOT. If it really is the case, it does indicate the transmission does use the TPS signal. Exactly how is the unknown here for me at least.

P0731 - 1st gear ratio error. I have read this can indicate clutch wear. I would bet you know CVIs may be worth checking or even checking fluid pressures. Course then as your saying, was this caused by the TPS signal? Me? I would start with the TPS. Just my 1/2 cents worth.

 

well i changed the TPS on my lunch break in the parking lot. i wont know if it changed anything until i go to drive home tonight. i tested the old TPS after the change and 9 times out of ten it shows good. that tenth time it shows an open right about where i would hold the throttle while driving 45 to 55 mph. it tested this way several times and now it is showing good all the time. the transmission codes cleared themselves some time between my check last night and this afternoon when i changed the TPS code. both TPS code were still present as i had not reset anything.
after the change i cleared the TPS codes. hopefully that got it and the hard downshift into first at 25 mph tripped the p1782 code. a shot like that could make some clutches slip..lol

 

after the drive home i can honestly say that it was the TPS. the surging and abrupt transmission shift are gone. the engine idles smoothly and does not miss a lick. the transmission is shifting better than it has in months (it appears that the TCM uses info from the TPS for shifting and torque converter lock up). none of the codes showed up after the last reset.

 

Great news. Thanks for sticking with us and posting the fix.

 

just an update. two weeks later and still running smooth. Gas mileage which was running about 21 mpg is now back up to 24. now it is time for a set of plugs and wires.