Manual Third Gear Engine Running

A manual 4-3 downshift is available to increase vehicle performance when the use of only three gear ratios is desired. Manual Third gear range also provides engine braking in Third gear when the throttle is released. A manual 4-3 downshift is accomplished by moving the selector lever into the Manual Third (D) position. This moves the manual valve and immediately downshifts the transmission into Third gear. Refer to Overdrive Range, 4-3 Downshift for a complete description of a 4-3 downshift. In Manual Third, the transmission is prevented, both hydraulically and electronically, from shifting into Fourth gear. The following information explains the additional changes during a manual 4-3 downshift as compared to a forced 4-3 downshift.

The selector lever moves the manual shaft and manual valve into the Manual Third position (D). This allows line pressure to enter the D3 fluid circuit.

D3 fluid is routed to the PSA and opens the normally closed D3 fluid pressure switch. The combination of the opened D3 switch and the closed D4 switch signals the PCM that the transmission is operating in Manual Third.

When Manual Third is selected, the PCM de-energizes the 1-2 shift solenoid to immediately downshift the transmission into Third gear. This electronically prevents Fourth gear.

D3 fluid pressure assists spring force to keep the valve in the downshifted position against the signal "A" fluid circuit. In this position, the valve blocks 3-4 signal fluid and the 4th signal fluid circuit is open to an exhaust port past the valve. Therefore, with D3 fluid pressure assisting spring force, Fourth gear is hydraulically prevented.

With the 2-3 shift solenoid de-energized and open, actuator feed limit (AFL) fluid acting on the 2-3 shuttle valve holds both valves in the upshifted position. This allows D3 fluid to feed the overrun fluid circuit through the 2-3 shuttle valve.

Overrun fluid pressure seats the ball against the empty D2 fluid circuit.

Overrun fluid pressure seats the #6 checkball and is orificed (#20) to fill the overrun clutch feed fluid circuit. This orifice controls the overrun clutch apply rate.

4th signal fluid pressure is exhausted from the end of the 3-4 relay valve. Overrun clutch feed fluid pressure assists spring force and closes both valves. This allows overrun clutch feed fluid to flow through the 4-3 sequence valve and fill the overrun clutch fluid circuit.

Overrun clutch fluid pressure moves the piston to apply the overrun clutch plates. The overrun clutch plates provide engine compression braking in Manual Third - Third Gear.

This ball and capsule is located in the overrun clutch fluid circuit in the oil pump. It allows air to exhaust from the circuit as fluid pressure increases and also allows air into the circuit to displace the fluid when the clutch releases.

The PCM de-energizes the TCC solenoid to release the converter clutch prior to downshifting, assuming the converter clutch is applied in Overdrive Range-Fourth Gear when Manual Third is selected. The PCM will re-apply the converter clutch in Manual Third-Third Gear only when vehicle speed is above approximately 121 km/h (75 mph).

The pressure control solenoid operates in the same manner as Overdrive Range, regulating in response to throttle position and other vehicle operating conditions.

In Manual Third, the transmission upshifts and downshifts normally between First, Second and Third gears. However, in First and Second gears, the 2-3 shift solenoid is energized and the 2-3 shift valve train is in the downshifted position. The 2-3 shuttle valve blocks D3 fluid from entering the overrun fluid circuit and opens the overrun fluid circuit to an exhaust port at the valve. This prevents overrun clutch apply and engine compression braking in Manual Third-First and Second Gears.

Manual Third Gear Hydraulic Fluid Flow

As vehicle speed increases further and other vehicle operating conditions are appropriate, the PCM de-energizes the normally open 2-3 shift solenoid in order to shift the transmission into Third gear.

De-energized (turned OFF) by the PCM, the solenoid opens and actuator feed limit (AFL) fluid exhausts through the solenoid.

Note: AFL fluid continues to feed the solenoid through orifice #29. However, the exhaust port through the solenoid is larger than orifice #29 to prevent a buildup of pressure in the AFL fluid circuit at the solenoid end of the 2-3 shift valve. Exhausting AFL fluid is represented by the arrows through the solenoid.

AFL fluid pressure at the 2-3 shuttle valve moves the valve train toward the solenoid. In the upshifted position, the following changes occur:

3-4 signal fluid unseats the ball and enters the 3-4 clutch fluid circuit.

3-4 clutch fluid pressure moves the piston to apply the 3-4 clutch plates and obtain 3rd gear. However, the 2-4 band must release as the 3-4 clutch applies.

3-4 clutch fluid pressure unseats the ball and fills the 3rd accumulator fluid circuit.

3rd accumulator fluid seats the ball against the orificed exhaust and is routed to the released side of the 2nd apply piston. Before the #7 checkball seats, air in the 3rd accumulator fluid circuit is exhausted through the orifice.

3rd accumulator fluid pressure acts on the release side of the 2nd apply piston and assists servo return spring force. The surface area on the release side of the piston is greater than the surface area on the apply side. Therefore, 3rd accumulator fluid pressure and servo return spring force move the 2nd apply piston against 2nd clutch fluid pressure. This action serves two functions:

1. Move the apply pin to release the 2-4 band.
2. Act as an accumulator by absorbing initial 3-4 clutch fluid to cushion the 3-4 clutch apply rate. Remember that the 3rd accumulator fluid circuit is fed by 3-4 clutch fluid.

3-4 clutch fluid pressure moves the valve against spring force. This opens the valve and allows 2nd fluid to feed the 2nd clutch fluid circuit through the valve.

The solenoid remains at approximately 90% duty cycle and routes AFL fluid into the 3-2 signal fluid circuit. 3-2 signal fluid pressure holds the 3-2 control valve against spring force, thereby blocking the 3rd accumulator and 3-4 clutch fluid circuits.

The 1-2 shift solenoid remains de-energized and signal "A" fluid is exhausted through the solenoid. Also, D432 fluid pressure from the 2-3 shift valve assists spring force to hold the 1-2 shift valve in the upshifted position.

Spring force holds the valve in the downshifted position, blocking 3-4 clutch fluid in preparation for a 3-4 upshift.

TCC Solenoid

Under normal operating conditions in Overdrive Range-Third Gear, the PCM keeps the normally open TCC solenoid de-energized. CC signal fluid exhausts through the open solenoid and spring force keeps the converter clutch apply valve in the release position. However, at speeds above approximately 121 km/h (75 mph), the PCM will command TCC apply in Third gear.