When the gear selector lever is moved to the Reverse (R) position (from the Park position) the following changes occur in the transmission's hydraulic and electrical systems:

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 into 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.