Here's what happens.
On the highway at 70mph, tranny downshifts all by itself. By slowing down a little, I can get it to shift back up. But then it does it again. This is random, sometime it drives for several miles without downshifting. Sometimes I have a hard time getting it to shift back up. A slight hill on the highway and it downshifts.

The shifting at lower speeds is also messed up with downshifting when it is not needed.

In drive and stopped, engine tends to stall when apply gas. Stalled engine has the oil light on. No P codes. Before the high speed downshifting started, the tranny would shift roughly as I came to a stop. The stalling might be caused by the tranny.

Tranny was rebuilt 20,000k miles ago by a shop that I have trusted for years. 153,000miles on caravan.

Ideas on the cause of this? Take it to the trusted shop or a dealership? DIY?

 

Welcome to DF
My first guess would be the TPS, It may get to a point were it thinks its wide open throttle,causing the transmission to down shift.Sure you can take the van to your trusted trans shop and ck for store codes in the TCM.And ck the CVI's too.

 

TCM is transmission control module, but what are TPS and CVI?
thanks
It's at a dealership getting diagnosed. Do independent garages have the ability to flash, to update etc that a dealership has?

 

ok, TPS is throttle position sensor. CVI is clutch volume index. What does the CVI measure? TPS seems self-explanatory.
thanks

 

The transmission clutches need to be set with a dial gauge and then the fluid needs to apply the clutches.So the fluid is an index on how much fluid it take to apply the clutches. CVI............Clutch Volume Index..

 

When it downshifts
Does it shift back up??

or are you then stuck in low gear?

Maybe no P codes but I'll bet there are some trans codes stored, most cheapo scanners dont even look for trans codes.
A decent trans shop will scan the trans codes for nuthin (bring the tech a coffee or somethin)

 

a decent corner garage, high school auto shop, local community technical college also has a real scanner than can check out trans codes

 

Dealership tells me that the TCM set a code "TPS intermittent". I didn't get the code number. They are replacing the TPS.

The tranny is not stuck in a low gear. It shifts back up. It acts fine sometimes. Like on the way to dealer service, shifted perfectly!

 

ya go hang out at your local high school, or college. sorry but where I live you need a pass to be anywhere on school property.

I prefer the people who dont mind walk in customers

Do the wiggle test on the TPS plug (on throttle body) seen at least 4 with faulty connections there.

 

too bad cuz the High schools around where I live welcome community members to participate in school functions.

the tech schools/community colleges by me do all kinds of work like this. They even have a night class anyone can take it goes from 6-10pm wednesday and cost $100 for 12 weeks of access to all the tools, equipment, scanners, and instructor knowledge. it's an open shop deal.