Hummer H2. Manual - part 2591

NEUTRAL - ENGINE RUNNING 

When the gear selector lever is moved to the Neutral position (N) from the Reverse position, the following 
changes occur to the transmission hydraulic and electrical systems. 

Manual Valve 

In the Neutral position, the manual valve blocks the line pressure from entering any other fluid circuits. Reverse 
and PR fluids exhaust past the manual valve. 

Lo and Reverse Clutch Releases 

Lo and Reverse Clutch Piston 

PR and Lo/reverse fluids exhaust from the piston, thereby releasing the lo and reverse clutch plates. Exhausting 
PR fluid unseats the lo and reverse clutch checkball (#10) for a quick exhaust. 

Lo Overrun Valve 

Spring force closes the valve when the PR fluid pressure exhausts. Lo/reverse fluid exhausts through the valve, 
into the Lo/1st fluid circuit, past the 1-2 shift valve, into the Lo fluid circuit and through an exhaust port at the 
manual valve. 

Reverse Input Cutch Releases 

Reverse Input Clutch Piston 

Reverse input fluid pressure exhausts from the piston, through the boost valve, past the #3 checkball and to the 
manual valve. With the reverse input fluid exhausted, the reverse input clutch plates are released and the 
transmission is in Neutral. 

Reverse Abuse Valve 

Reverse fluid pressure exhausts and spring force closes the valve. 

Boost Valve 

Reverse input fluid pressure exhausts and line pressure returns to the normal operating range as in the Park and 
Overdrive positions. 

Reverse Input Checkball (#3) 

Exhausting reverse input fluid unseats the ball for a quick exhaust through the reverse fluid circuit and past the 
manual valve. 

Transmission Fluid Pressure (TFP) Manual Valve Position Switch Assembly 

 

2004 Hummer H2 

2004 TRANSMISSION/TRANSAXLE Automatic Transmission - Overhaul - 4L60-E/4L65-E

  

Reverse input fluid exhausts from the TFP manual valve position switch. With no other fluid routed to it, the 
TFP manual valve position switch signals the PCM that the transmission is operating in either Park or Neutral.

IMPORTANT: In Park, Reverse and Neutral the shift solenoid valves are shown energized. 

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 vehicle speed. For example, if Neutral is selected when the 
transmission is operating in Second Gear, the shift solenoid valves will remain 
in a Second Gear state. However, with the manual valve blocking line pressure, 
the shift solenoid valve states do not affect transmission operation in Park, 
Reverse and Neutral.

 

2004 Hummer H2 

2004 TRANSMISSION/TRANSAXLE Automatic Transmission - Overhaul - 4L60-E/4L65-E

  

Fig. 325: Neutral - Engine Running 
Courtesy of GENERAL MOTORS CORP.

 

2004 Hummer H2 

2004 TRANSMISSION/TRANSAXLE Automatic Transmission - Overhaul - 4L60-E/4L65-E

  

OVERDRIVE RANGE, FIRST GEAR 

When the gear selector lever is moved to the Overdrive position, from the neutral position, the following 
changes occur to the transmission's hydraulic and electrical systems: 

Manual Valve 

Line pressure flows through the manual valve and fills the D4 fluid circuit. All other fluid circuits remain empty 
with the manual valve in the Overdrive position. 

Forward Clutch Applies 

Forward Clutch Accumulator Checkball (#12) 

D4 fluid pressure seats the checkball and is orificed (#22) into the forward clutch feed fluid circuit. This orifice 
helps control the forward clutch apply rate. 

Forward Clutch Accumulator Piston 

Forward clutch feed fluid pressure moves the piston against spring force. This action absorbs some of the initial 
increase of forward clutch feed fluid pressure to cushion the forward clutch apply. 

Forward Clutch Abuse Valve 

D4 fluid pressure acts on the valve opposite of spring force. At engine speeds greater than idle, D4 fluid 
pressure increases and moves the valve against spring force (as shown). D4 fluid can then quickly fill the 
forward clutch feed fluid circuit, thereby bypassing the control of orifice #22 and providing a faster apply of the 
forward clutch. Otherwise, with increased throttle opening and engine torque, the clutch may slip during apply. 

Transmission Fluid Pressure (TFP) Manual Valve Position Switch Assembly 

D4 fluid pressure is routed to the TFP manual valve position switch and closes the normally open D4 fluid 
pressure switch. This signals the PCM that the transmission is operating in Overdrive range. 

1-2 Shift Solenoid (SS) Valve 

Energized (ON) as in Neutral, the normally open solenoid is closed and blocks signal A fluid from exhausting 
through the solenoid. This maintains pressure in the signal A fluid circuit. 

2-3 Shift Solenoid (SS) Valve 

Energized (ON) as in Neutral, the normally open solenoid is closed and blocks signal B fluid from exhausting 
through the solenoid. This maintains signal B fluid pressure at the solenoid end of the 2-3 shift valve. 

2-3 Shift Valve Train 

Signal B fluid pressure at the solenoid end of the 2-3 shift valve holds the valve train in the downshifted 
position against AFL fluid pressure acting on the 2-3 shift valve. In this position, the 2-3 shuttle valve blocks 

 

2004 Hummer H2 

2004 TRANSMISSION/TRANSAXLE Automatic Transmission - Overhaul - 4L60-E/4L65-E