Subaru 2002 Impreza Service Manual page 246

TRANSMISSION CONTROL MODULE (TCM)
I
Automatic Transmission
I: LEARNING CONTROL
The TCM has a learning control function with which it can adapt gear shift timing optimally to the
current vehicle conditions by updating correction factors in the memory.
For this reason, gear shift shock may become larger after the power supply is interrupted (discon-
nection of battery, flat battery, etc.) or immediately after the ATF is replaced.
Larger gear shift shock after power supply interruption occurs because the correction data is reset
to those for the new vehicle condition.
The TCM starts learning function again as soon as the power supply is restored. After driving for
a while, therefore, the transmission will become able to make gear shifts at the optimum timing.
Larger shift shock immediately after ATF change is caused by change in friction characteristics
of the transmission internal parts. Also in this case, the transmission recovers shockless gear shift-
ing after driving for a while.
--
AT-24