As the speed of the vehicle continues to increase, the powertrain control module (PCM) monitors the input signals from various engine and transmission sensors. The PCM uses this data to energize the 1-2, 3-4 shift solenoid (SS) valve in order to shift the transmission into fourth gear at the appropriate time.

Energizes to prevent fluid from exhausting out of the line passage and the 1-2, 3-4 signal fluid passage.

Is held against 1-2, 3-4 signal fluid pressure by spring pressure and 2-3 off signal fluid pressure at the end of the valve.

When 1-2, 3-4 signal fluid shifts the 3-4 shift valve against spring force, it allows 3rd fluid to enter the 4th clutch fluid passage. 4th clutch fluid is forced through a feed orifice before stroking the 3-4 accumulator piston (428) and applying the fourth clutch.

4th Clutch fluid pressure applies the fourth clutch to shift the transmission to fourth gear.

Remains applied, but is ineffective.

Overruns as fourth clutch is applied. In third gear, the input clutch is released allowing input clutch apply fluid to exhaust through the 3-4 shift valve (362) into the input clutch feed passage. At the 2-3 shift valve (357), exhausting input clutch apply fluid is directed into the D3 passage and out the manual valve (404).

Remains applied.

Remains applied, but is ineffective.

Continues to overrun.

4th clutch fluid is also routed to the 3-4 accumulator piston. 4th clutch fluid pressure moves the piston against spring force and 3-4 accumulator feed fluid pressure. This action absorbs initial 4th clutch fluid pressure to cushion the 4th clutch apply. The movement of the 3-4 accumulator piston forces some accumulator fluid out of the accumulator.

Excess 3-4 accumulator feed fluid is routed back to the 3-4 accumulator valve. This fluid pressure moves the accumulator valve against spring force and torque signal fluid pressure to regulate the exhaust of excess accumulator fluid. This regulation provides additional control for the fourth clutch apply.

TCC apply could vary depending on vehicle application and may be calibrated to apply in Overdrive Range -- Fourth Gear.

Release fluid pressure routed to the TFP manual valve position switch signals the PCM that the TCC is released.