I got to wondering today about why my car shifts differently after it's warmed up. Cold shifts are very hard, when it's hotter it has that rubber band effect...

So I understand that the PCM controls the shift firmness, but what does it use as a basis for that? Is it engine temp or some other sensor that I don't know about?

 

There are several tables in the PCM that change the pressure in relation to temperature. There are also some that use throttle position.

 

It's because the oil is cold, therefore more dense when you first drive the car. Once the car is warmed up, the oil is hot, less dense, and doesn't pack the same "punch" when it shifts.

That's it in a nutshell.