Transmission Downshifting

2002 Tundra SR5
4.7L, 2WD
252,000 miles

Hello,
I am experiencing shifting issues. The transmission has been shifting through all the gears flawlessly as its done from day 1. However, I have recently noticed that the transmission will downshift from 4th to 3rd gear when driving on level roads without acceleration.

I'm not sure what is causing this but my thoughts are that whatever controls the shifting may be receiving bad data. This is where I could use some help. I am wondering how the computer controls the shift points. I would guess that that is where my issue lies.

Any Help is Appreciated
Thank You

 

Are you hitting the brakes at all before it downshifts?

First thing I would do is disconnect the negative battery terminal for at least 30 mins. This will “reset” all shift points. Over time these ecu’s will learn and adapt to the way a person drives.

 

I'd check the trailer light plug. If it's corroded, you could get stray voltage accross the pins, thus causing OD to be kicked off via back feed to the ECU.

 

Hello,
No corrosion on the trailer plug and no, I'm not hitting the brakes. This issue just started about a month ago. I noticed it on a roadtrip.

I was thinking that it I could have a vacuum leak. But I just don't know what controls the shifting on this truck.

Thank you for the advise.
I do appreciate it.