I have a 2000 S10 2.2L. It recently started randomly shifting from 4th back to 3rd between 2000 - 3000 rpm. I drive it 45 miles one way to work and it starts doing it after about 30 miles or 30 minutes. It will just randomly shift down and then back up. I can get it to shift back to 4th by accelerating lightly. It doesn't seem to be completely related to load or speed and doesn't do it constantly. As this transmission is electronically controlled, I suspect an electrical issue but not ruling out mechanical. I have rebuilt manual transmissions but am not that familiar with the inner workings of automatics, especially electronically controlled. What systems are involved in the shifting between 3rd and 4th? I've done some research but haven't found anything specifically related to this. Can someone tell me what to check or how to troubleshoot this issue?

Thanks

 

Do a drain and fill of your trans fluid. (ie, 2-4 quart by bottom drain pan, is a drain&fill, not all fluid is replaced). Do not get a hot flush at the dealer at this time.

Check for metal parts in the drain.

Refill and insure you follow all instructions for proper level (while running, at temperature, on the level). A little under is better than a little over. never put it to the max.

before you do that, nothing can be said

 

the future: do NOT do these until after the first suggestions

* my chevy has a physical shifter for the automatic transmission. it's adjustable linkage. i had to adjust it once.

* the is "a fluid circuit" made of pipe-circuit, many check-***** and a few solenoid. it controlls shifting by pressure. if dirtied by lack of fluid changes it can cause problems

* ODBII checkers with "transmission check code" ability are cheaper than ever. give us the code!

anything more is TMI

 

Thank you.

I had planned to do a fluid/filter change this weekend or as soon as possible and check for contaminates. I also had a code set last night, P1870 which would be consistent with the symptoms. I will follow up with what I find.