When the gear selector lever is moved to the Drive (D) position from the Neutral (N) position, the following changes occur in the transmission's hydraulic and electrical systems in order to start the vehicle moving from a stopped position:

Pressure Control (PC) Solenoid 3 Trim

The PC solenoid 3 trim is energized (ON) allowing actuator feed limit fluid to enter the PCS 3 signal circuit. PCS 3 signal fluid is then routed through orifice #34 to the hybrid low, 1-2 clutch regulator valve; through orifice #33 to the hybrid low, 1-2 clutch boost valve; and to the shift solenoid valve - mode B.

Hybrid Low, 1-2 Clutch Regulator Valve

PCS 3 signal fluid, at the hybrid low, 1-2 clutch regulator valve, opposes hybrid low, 1-2 clutch regulator valve spring force and HL 12 clutch/4th clutch feedback fluid pressure to regulate line or auxiliary line pressure into the HL 12 clutch/4th clutch feed circuit.

Hybrid Low, 1-2 Clutch Boost Valve

PCS 3 signal fluid pressure acts on a differential area of the hybrid low, 1-2 clutch boost valve, moving the valve against hybrid low, 1-2 clutch boost valve spring force to regulate HL 12 clutch/4th clutch feed fluid into the HL 12 clutch/4th clutch feedback circuit. As PCS 3 signal fluid pressure is increased to a given value, the hybrid low, 1-2 clutch boost valve opens the HL 1-2 clutch/4th clutch feedback circuit to exhaust. This results in the hybrid low, 1-2 clutch regulator valve moving to the full feed position, sending full HL 12 clutch/4th clutch feed pressure (full line pressure) to the hybrid low, 1-2 clutch.

Shift Solenoid Valve - Mode B

HL 12 clutch/4th clutch feed fluid is routed to the shift solenoid valve - mode B, where it passes through the valve in the HL 12 clutch circuit.

Hybrid Low, 1-2 Clutch Assembly

HL 12 clutch fluid pressure enters the rear case assembly behind the hybrid low, 1-2 clutch piston and moves the piston against spring force to apply the hybrid low, 1-2 clutch plates.