GM Service Manual Online
For 1990-2009 cars only

For a view of the oil flow diagram, refer to the 1996 TURM Manual.

When you move the gear selector lever from the Reverse position to the Neutral position, the following changes occur to the hydraulic and electrical systems.

Reverse Clutch Releases

Manual Valve: The manual valve is moved to the Neutral position, where the valve blocks the line pressure from entering the Reverse fluid circuit. The reverse fluid circuit is opened to an exhaust at the manual valve.

Reverse Clutch: Reverse fluid exhausts from the reverse clutch and the clutch releases. This action shifts the transmission in to Neutral position.

Boost Valve: Reverse fluid exhausts from the boost valve and line pressure regulation returns to the normal operating range.

A/T Fluid Pressure Manual Valve Position Switch (TFP Val. Position Sw.) Assembly: Reverse fluid pressure exhausts from the TFP Val. Position Sw. Assembly. This action signals the PCM that the transmission is either in Neutral (N) or Park (P) position.

Low and Reverse Band Remains Applied

1-2 Shift Solenoid Valve: As in Park and Reverse positions, the solenoid valve is energized and 1-2 signal fluid pressure acts on the 1-2 shift valve.

1-2 Shift Valve: The 1-2 signal fluid pressure keeps the 1-2 shift valve in the downshifted position. Low/PRN fluid continues to feed the low band fluid circuit.

Low and Reverse Servo: Reverse fluid exhausts from the servo. However, low band fluid pressure continues to act on the inner area of the servo piston in order to keep the band applied.

Important: In Park, Reverse, and Neutral positions the shift solenoid valves are shown to be in the First gear state. this is the normal operating state when the vehicle is stationary or at low vehicle speeds. However, the PCM will change the shift solenoid valve states depending on the speed of the vehicle. For example, if the Neutral range is selected when the vehicle is operating in Second gear, the shift solenoid valves will remain in a Second gear state. But with the manual valve in Neutral, line pressure is blocked, drive fluid exhausts and the transmission will shift into Neutral.