Random downshifting problem in an automatic transmission

[aldrake419]

I have recently noticed that my 03 protege DX model randomly downshifts on me when letting off the gas pedal, the transmission is automatic. Any help would be appreciated, thanks!

 

[concept]

When was the last time you changed the transmission fluid? Have you checked its level, lately?

 

[Merryfrankster]

When was the last time you changed the transmission fluid? Have you checked its level, lately?

I'm having the same problem with an 02 Protege5 with auto-manual, in auto mode. I just bought this car recently. The fluid in the trans was junk. So I started out by servicing the trans. Drain, open, replace filter, close, refill 3 qts, then bleed one quart at a time through cooler hose until it all turns pink (five quarts needed). Verified level at temperature. Not to open a dead debate, but I used Mercon V. Yes, I know it is not the same as M-V. But even Mazda dealers use Mercon V, so I feel it's ok. And besides, I use Mercon V on the other 11 Proteges in my fleet, and have not had a problem in five years related to use of Mercon V. So I am ruling out Mercon V as the cause of the problem, which is this: When I let off the gas pedal, in auto mode, the trans does a hard downshift. This can be from 4 to 3, or from 3 to 2. This seems very much like the problem described in this thread, so I am wondering if anyone knows the answer, before I go tearing into this thing even more. I just recently bought another 2002 with blown engine just for parts, so I could start swapping trans parts one by one until the thing works, but I am hoping someone can save me the trouble. Anyone, please?

 

[concept]

I did see this suggestion:

It sounds like the Vehicle Speed Sensor has a problem. The VSS signal gets lost, speedo drops to zero, PCM thinks speed drops and tells the transaxle to downshift to the appropriate gear.

It does look plausible.

 

[Merryfrankster]

I'm not seeing any weirdness on the speedometer, so, I don't know. But as soon as I get a hold of a spare, I'll swap the Vehicle speed sensor VSS, if only just to rule it out as the fault. Along the same line of reasoning of the TCM getting wrong data, I am also suspecting the Throttle Position Sensor TPS. This is without any knowledge of the working logic of the TCM - i.e. does it use TPS data, or not, to determine shift points. It's worth a try anyway. I have spare parts lying around for a swap.

 

[concept]

In doing a quick search, it does look like this is not uncommon among other vehicles, as well. But if you can locate a post (specifically a Mazda one) in which the OP reports a solution, it may save you a bunch of swapping time.
The answer I posted, above was posted (different forum) in response to a description of tranny strangeness that looked similar to yours.

 

[Merryfrankster]

With a lot of searching, more than I care to admit to, I've seen a lot of speculative suggestions, but I have yet to see a bona fide reported solution, where someone says: "I did this, and it solved the problem."

 

[Merryfrankster]

I took the VSS from one of my good cars and put it in the bad car. No noticeable effect. Then I put the VSS from the bad car in the good car. The good car stayed good. I think this rules out the VSS.

 

[Merryfrankster]

I found the answer to this and I posted it in another thread. It was the TPS, not the VSS. If you're interested, just look up my postings and you will find it.

 

[concept]

Strange, but definitely good to know. Thanks for the feedback.