I have a 2006 Mazda 3 2.0L. I bought it from a private seller so i don't know the extent of any problems before I got it. The car was manufactured in late 2005, so it doesn't have the separate TCM, mounted on top of the transmission that started with the 2006 models. I had to change the transmission seal on the divers side because the previous owner had replaced the half shaft and messed up the seal when putting the shaft back in.
With that out of the way...now for the problem.
It started after I had replaced the seal.
From a dead stop the car will go into 1st, but unless I'm going full throttle, it will almost immediately try to go into 2nd and then almost as quickly try to go into 3rd. However when it tries to go into 3rd, it doesn't, just acts like I've put the car into neutral, if I continue to press on the accelerator and rev the engine up to around 3500rpms it will try and shift into 4th and then back down to 3rd. when this first happened I got a AT light on the dashboard, code was telling me solenoid 1 was stuck open. Bought a new solenoid kit and replaced all 6, along with the transmission filter and some new fluid. Now the car drives fine in 1st and 2nd gear, but still the same issue when trying to go into 3rd, acts like I've put it in neutral, but no AT or Check Engine lights come on. I can put the car in "manual" and drive around in 1st and 2nd gear without any problems.
I'm really not sure what is going on. I was thinking about maybe an ECU issue, or even worse a transmission problem that I don't have money to replace at the moment.
Thanks for any advice

 

Welcome to the forum

 

What was the miles of the last basic transmission service before you’DIY one . What you’re describing sounds like a neglected transmission.
when you dropped the pan how much was attached to the pan magnet and how much dark and thick settled fluid at the bottom of the pan? Also did you wipe down the valvebody and maybe spray the everything you could see with WD40? If the fluid was dark then you only replaced about 1/3 of the total volume so you may need to do a drain pan and replace only the fluid a couple more time to help the cleaning process? Iam not an advocate of the dilution method as its results are no where near as good as having a service shop the has a specialized transmission service machine do the job .


It is not likely the ECU or if you scanned it completely you would have found more DTCs that would at least indicate a possible ECU/TCM program issue.


Btw it does help us to help you if you post any ECU DTCs or other fault indicators.
There are three areas in an ECU you should have scanned for basic info.

 

Yikes.
Sounds like bad/wrong ATF or changing the seal a piece of debris made its way into valve body.
Or the Shift solenoid.

Pete

 

Pete, Welcome to the forum
An interesting first response as a new member to a forum???
Not sure how you "guessed' or arrived at that conclusion? But its not accurate based on the first response by the OP. And if one of those 2 things did happen the description of the shifting would be much different. As for the wrong oil pretty much the same thing, if it had a complete fluid change with the badly chosen ATF it would take a few years of service and more like 30-70k miles to see the effect and there would have been other minor telltale signs . Again NOT what the OP described.
My guess is that you have never completely taken any automatic transmission completely apart?

ASE