As vehicle speed increases and operating conditions become appropriate, the transmission control module (TCM) processes input signals from the input and output speed sensors, the throttle position (TP) sensor and other vehicle sensors to determine the precise moment to de-energize or "turn OFF" the normally low pressure control solenoid 4 trim, to command ON the normally high pressure control solenoid 2 trim, and shift the transmission into Second Gear:

Pressure Control (PC) Solenoid 4 Trim

The PC solenoid 4 trim is commanded OFF, allowing PCS 4 signal fluid to exhaust from the 1-3 clutch regulator valve.

1-3 Clutch Assembly

13 clutch fluid pressure is exhausted from the center support assembly, allowing 1-3 clutch spring force to move the 1-3 clutch piston and release the 1-3 clutch plates.

Shift Solenoid Valve - Mode A

Exhausting 13 clutch fluid pressure passes through the shift solenoid valve - mode A into the 13 clutch/A cooling feed circuit.

#2 Encapsulated Ball Check Valve

13 clutch feedback fluid pressure exhausts into the 13 clutch/A cooling feed circuit, allowing actuator feed limit fluid to seat the ball.

1-3 Clutch Regulator Valve

1-3 clutch regulator valve spring force moves the 1-3 clutch regulator valve to the released position, allowing 13 clutch/A cooling feed fluid pressure to exhaust through the valve into the backfill circuit.

Clutch Piston Exhaust Blowoff Ball Valve

Excess fluid pressure in the backfill circuit exhausts at the clutch piston exhaust blowoff ball valve in order to maintain a constant backfill fluid pressure of 2 psi.

Pressure Control (PC) Solenoid 2 Trim

The PC solenoid 2 trim is energized (ON) allowing actuator feed limit fluid to enter the PCS 2 signal circuit. PCS 2 signal fluid is then routed through orifice #38 to the hybrid direct, 2-3-4 clutch regulator valve.

Hybrid Direct, 2-3-4 Clutch Regulator Valve

PCS 2 signal fluid, at the hybrid direct, 2-3-4 clutch regulator valve, opposes hybrid direct, 2-3-4 clutch regulator valve spring force and HD 234 clutch feedback fluid pressure to regulate line or auxiliary line pressure into the HD 234 clutch/B cooling feed circuit.

#1 Encapsulated Ball Check Valve

HD 234 clutch feedback fluid unseats the #1 ball check valve, allowing excess pressure to pass into the actuator feed limit circuit. This helps to control clutch apply fluid pressure and clutch apply feel.

Shift Solenoid Valve - Mode A

HD 234 clutch/B cooling feed fluid passes through the shift solenoid valve - mode A into the HD 234 clutch supply fluid circuit and is routed to the shift solenoid valve - mode B.

Shift Solenoid Valve - Mode B

HD 234 clutch supply fluid passes through the shift solenoid valve - mode B into the HD 234 clutch circuit and is routed to the hybrid direct 2-3-4 clutch assembly.

Hybrid Direct, 2-3-4 Clutch Assembly

HD 234 clutch fluid is directed to the hybrid direct, 2-3-4 clutch piston to apply the hybrid direct, 2-3-4 clutch plates and achieve second gear.

Shift Solenoid Valve - Mode B

HD 234 clutch/B cooling feed fluid is routed to the shift solenoid valve - mode B where it is blocked by the valve in preparation for an upshift to third gear.