Park or Neutral-Engine Running

Description and Operation Neutral- Engine Running





Neutral Hydraulic Schematic

In N (Neutral), A Trim Solenoid is in its normally closed state (de-energized), B Trim Solenoid is in its normally open state (de-energized), C, D, and E Solenoids are energized, and Trim Solenoid F remains de-energized.

C, D, and E Solenoids supply control main pressure to the top of Shift Valves C, D, and E, moving the valves downward against spring force.

With Shift Valve C stroked down, control main pressure is directed through Shift Valve C to pressure switch C, turning the switch on. With Shift Valve D down, the exhaust path is blocked for the control main pressure being supplied through an orifice to the D pressure switch, and the pressure raises to control main and the D pressure switch turns on. With Shift Valve E down, the exhaust path is blocked for the control main pressure being supplied through an orifice to the E pressure switch, and the pressure raises to control main and the E pressure switch turns on. With Pressure Switches C, D, and E ON, feedback is provided to the Transmission Control Module (TCM) that Shift Valves C, D, and E are stroked.

Normally closed A Trim Solenoid blocks the exhaust of the A trim signal pressure, raising the trim signal pressure. The A trim signal pressure forces Trim Valve A down, raising the A trim pressure which is directed to Shift Valve D. In its downward position, Shift Valve D routes fluid to C5 clutch, applying the clutch. All other clutches are exhausted.

With only one clutch applied, the transmission is in N (Neutral).

If electrical power is interrupted while N (Neutral) is selected, C, D, and E Solenoids are de-energized and Shift Valve C moves upward. Due to valve timing, when power is lost, Shift Valve C strokes faster than Shift Valve E. When Shift Valve C strokes up, control main pressure is fed through Shift Valve C to the top of Shift Valve E, keeping the valve down. Normally closed A Trim Solenoid continues to block the exhaust of the solenoid signal pressure (solenoid signal remains control main). The solenoid signal pressure on top of Trim Valve A produces maximum trim pressure, which is routed to Shift Valve D. Shift Valve D stayed down due to the "latching" effect of C5 clutch pressure acting on two different diameter lands. In its downward position, pressure continues to be routed to C5 clutch, keeping the clutch applied. Since only one clutch is applied, the transmission remains in N (Neutral).

If electrical power is interrupted with the transmission in N (Neutral) and the manual selector valve is moved to forward or R (Reverse), the transmission stays in N (Neutral) because Shift Valve E stays down and main pressure is blocked from reaching the Manual Selector Valve.


If the engine is shutdown and restarted with the electrical power interrupted to the TCM, Shift Valves C, D and E will remain up. Normally closed A Trim Solenoid blocks the exhaust of the A trim signal pressure (trim signal pressure becomes control main). The solenoid signal pressure on top of Trim Valve A produces maximum Trim pressure, which is routed to Shift Valve D. In its upward position, Shift valve D routes fluid to C3 clutch. All other clutches are exhausted, so the transmission remains in N (Neutral). When Shift Valve E is up, main pressure is routed through Shift Valve E to the manual selector valve. If forward is selected, the manual selector valve routes fluid to C1 clutch. C3 clutch remains on with C1, resulting in third range being attained for limp home capability. If R (Reverse) is selected, the selector valve directs fluid through the TCC Valve and Shift Valve D to C5 clutch. C3 clutch remains on with C5 clutch, resulting in R (Reverse) range being attained.