Originally Posted by JCL

Ghost-Flame:

The following will explain the background on adaptive transmission shifts. These are BMW training materials that cover this. Essentially, when automatic transmissions became electronic, manufacturers gained control over shifting, and then in a further development, gained the ability to measure shift performance, and adapt clutch pressures based on shift times. They measure slip (difference between input and output speeds) and adjust for clutch wear, among other things. That is what gets invalidated when the fluid is changed, as the transmission has stored the expected shift characteristics. Your transmission shop will know the importance of clearing those adaptations with a computer diagnostic tool when they change fluids on a BMW (and the same applies to many other makes of vehicle). The following are BMW materials, so they apply to both the GM and ZF transmissions. They are worth reading through, IMO.

Transmission Fundamentals Part 1

Transmission Fundamentals Parts 2

Electronic Transmission Control Part 1

Electronic Transmission Control Part 2