When the gear selector lever is in the Park (P) position and the engine is running, fluid is drawn into the fluid pump and line pressure is directed to the pressure regulator valve.

Backfill Fluid Circuit

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.

Clutch Piston Exhaust Blowoff Ball Valve

Backfill fluid is constantly limited to a pressure of 2 psi by the action of the clutch piston exhaust blowoff ball valve. When fluid pressure in the backfill circuit begins to exceed 2 psi, the ball moves against spring pressure allowing the excess fluid pressure to exhaust into the sump.

Hybrid Low, 1-2 Clutch Regulator Valve

Line or auxiliary line fluid is routed through orifice #9 to the hybrid low, 1-2 clutch regulator valve in preparation for a shift.

1-3 Clutch Regulator Valve

Line or auxiliary line fluid is routed through orifice #11 to the 1-3 clutch regulator valve in preparation for a shift.

Hybrid Direct, 2-3-4 Clutch Regulator Valve

Line or auxiliary line fluid is routed through orifice #10 to the hybrid direct, 2-3-4 clutch regulator valve in preparation for a shift.

Auxiliary Line Boost Valve

Line or auxiliary line fluid is routed through orifice #12 to the auxiliary line boost valve in preparation for a shift to EVT mode.