Backfill Fluid Circuit
WARNING: This page is about a different car, the 2010 GMC Sierra and 2010 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Fed by fluid from the actuator feed limit circuit, through orifices #21, 22, 23, and 24, the backfill circuit is always filled with low pressure fluid. This fluid fills the various clutches and their supply circuits in preparation for a shift. Fluid pressure is not strong enough to move the clutch pistons against spring pressure, but fills the circuits allowing for quick pressurization and fast clutch apply when the TCM determines that conditions are appropriate to apply a clutch.