If the transmission is in First or Second gear during a transmission electrical component malfunction, the transmission will defualt to Low. All solenoids will default to their normal state. This default action enables the vehicle to be safely driven to a service center.

Pressure Control (PC) Solenoid 3 Trim

The PC solenoid 3 trim defaults to its normally high state (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 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 block HL 12 clutch/4th clutch feed fluid from entering the HL 12 clutch/4th clutch feedback circuit, and opening the HL 12 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.

Hybrid Low, 1-2 Clutch Regulator Valve

PCS 3 signal fluid moves the hybrid low, 1-2 clutch regulator valve, against hybrid low, 1-2 clutch regulator valve spring force, to the applied position. This allows line or auxiliary line fluid to pass through the valve into the HL 12 clutch/4th clutch feed circuit.

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.

1-3 Clutch Releases

If the transmission is operating in First gear when an electrical malfunction occurs, the normally closed shift solenoid 1 and the normally low pressure control solenoid 4 trim default to their normal states (OFF) and the 1-3 clutch is released. Refer to Drive Range, Second Gear for a complete description of 1-3 clutch release.

If the transmission is operating in Second gear when an electrical malfunction occurs, the shift solenoid 1 defaults to its normally closed state (OFF) and the hybrid direct, 2-3-4 clutch is released.

Shift Solenoid 1

The shift solenoid 1 defaults to its normally closed state (OFF), allowing solenoid 1 signal fluid to exhaust from the shift sloenoid valve - mode A, the hybrid direct, 2-3-4 clutch regulator valve, and the 1-3 clutch regulator valve.

Hybrid Direct, 2-3-4 Clutch Assembly

HD 234 clutch fluid pressure is exhausted from the rear case assembly, allowing hybrid direct, 2-3-4 clutch spring force to move the hybrid direct, 2-3-4 clutch piston and release the hybrid direct, 2-3-4 clutch plates.

Shift Solenoid Valve - Mode B

Exhausting HD 234 clutch fluid pressure passes through the shift solenoid valve - mode B into the HD 234 clutch supply circuit.

Shift Solenoid Valve - Mode A

Shift solenoid valve - mode A spring force moves the shift solenoid valve - mode A to the released position, allowing HD 234 clutch supply 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.