2010 m3 2.5 automatic downshifts not smooth

Hey everyone,

I have a 2010 Mazda 3 2.5l automatic at 56k miles

I recently cleaned the MAF/throttle body since i was having vibrations while idling which solve the issue.

Short after i noticed when slowing down the transmission typically "down" shifts for you. However i notice its not doing it near as smooth, and sometimes i can hear sort of a sound (hard to describe not to loud).

It only does this once warmed up, and typically when decellerating to stop. I noticed when it happens the RPM are pretty low like its hanging onto the last gear before it shifts down again. I inspected my trans fluid..it was dark. SO i replaced the fluid. But still notice the downshift isnt so smooth sometimes. Typical accelerating is not a problem. If i put the trans into that electronic shifting thing, it shifts perfectly fine.

I pulled the negative from the battery. No help. Not sure what to do or expect from this? If it needs a new trans ill probably sell the car but looking for your guys expereiince/ advice. Ive read something about transmission ECU firmware update? Idk?

lol
any help is appreciated much

Make sure you follow the transmission fluid level-checking procedure, exactly as written in your owner's manual. Underfilling or overfilling can cause symptoms that include what you describe. It's highly unlikely your transmission is fried, unless the fluid had never been changed according to the intervals specified in the manual.

thats the thing, there is no service interval in the manual. When i "manually" shift it its smooth. So it seems like the shift points from the computer, rather than a failure. but the fluid was pretty much black. which i read happens a lot to these cars

I would drain and fill, again after 6000 miles, and then check the fluid color every 6 months. Changing the fluid every 2 years is a good habit to get into, IMO.

thanks for the response guys. Ill drain and fill again appreciate your responses!

just following up on this (i know im late) thanks a ton Concept.

It took 2 changes of the fluid but it fixed the issue. Thanks a TON.

That's good to see, Codeman. My son just picked up a 2012 3 2.0 with 55,000 miles on it. We will take a look at the trans fluid color and drain/fill.