Smooth Lockup Control
WARNING: This page is about a different car, the 2008 Subaru Tribeca, 2008 Subaru Outback, and 2008 Subaru Legacy. However, it is still accessible from the selected car via links, so may be relevant.
During the transition period from the lockup (disengaged) state to the lockup engaged state, the TCM controls the current output to the lockup solenoid. By changing the current output to the lockup solenoid and gradually raising the lockup clutch pressure, the lockup clutch piston is first put in a partially engaged state and its pressure is gradually increased to reduce shock.