Hummer H3. Manual — part 875

Fig. 495: Manual Third Gear Hydraulic Circuit Diagram
Courtesy of GENERAL MOTORS CORP.

MANUAL SECOND GEAR

A manual 3-2 downshift can be accomplished by moving the gear selector lever into the Manual
Second (2) position when the transmission is operating in third gear. This causes the transmission
to shift immediately into second gear regardless of vehicle operating conditions. Also, the
transmission is prevented from operating in any other gear, first, third or fourth. The following
information explains the additional changes during a manual 3-2 downshift, as compared to a
forced 3-2 downshift. Some vehicles in manual second gear will start out in first gear, while other
vehicles will have a second gear start. Refer to the owners manual for specific applications.

Manual Valve

The selector lever moves the manual shaft and the manual valve into the manual second (2)
position. This allows the line pressure to enter the D2 fluid circuit.

Transmission Fluid Pressure (TFP) Manual Valve Position Switch Assembly

The D2 fluid is routed to the TFP manual valve position switch where it opens the normally
closed D2 fluid pressure switch. With the D2 and the D3 pressure switches closed and the D4

2007 Hummer H3

2007 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - H3

pressure switch open, the TFP manual valve position switch signals the PCM that the transmission
is operating in manual second.

Third and Fourth Gears Prevented

2-3 Shift Solenoid (SS) Valve

The PCM energizes the 2-3 SS valve and the AFL fluid pressure holds the 2-3 shift valve in the
downshift position. This electronically prevents operation of the third and fourth gears.

2-3 Shift Valve Train

The D2 fluid is routed between the 2-3 shuttle and the 2-3 shift valves and causes the following:

Regardless of the operating conditions, the D2 fluid pressure holds the 2-3 shift valve in the
downshift position against the AFL fluid pressure.

The 2nd fluid is blocked from entering the 3-4 signal fluid circuit and the 3-4 signal fluid
circuit is open to an exhaust port at the valve.

The 3-4 clutch cannot apply with the 3-4 signal fluid exhausted. Therefore, third and fourth
gears are hydraulically prevented.

The 2nd fluid feeds the servo feed fluid circuit, but the 2nd fluid circuit has no function in
manual second.

The AFL fluid is blocked by the 2-3 shift valve and the D432 fluid circuit is exhausted
through the valve.

The overrun fluid is exhausted through the 2-3 shuttle valve.

1-2 Shift Valve

The 1-2 SS valve is OFF, the signal A fluid exhausts through the solenoid and the spring force
holds the valve in the upshifted position.

First Gear Prevented

The prevention of first gear is controlled electronically by the PCM through the 1-2 SS valve.
The PCM keeps the 1-2 SS valve de-energized, regardless of the vehicle operating conditions
when the TFP manual valve position switch signals manual second gear range. This keeps signal
A fluid exhausted and the spring force holds the 1-2 shift valve in the upshift position.

Overrun Clutch Remains Applied

Overrun Clutch Feed Checkball (#5)

2007 Hummer H3

2007 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - H3

Orificed D2 fluid pressure seats the #5 checkball against the empty overrun clutch fluid circuit.
This is done simultaneously with the overrun clutch fluid exhausting so that there is a continuous
fluid supply to the overrun clutch feed fluid circuit.

Overrun Clutch Piston

A continuous supply of fluid pressure is routed to the piston in order to keep the overrun clutch
plates applied.

Torque Converter Clutch

The converter clutch is released prior to downshifting into manual second-second gear. Under
normal operating conditions, the TCC will not apply in second gear.

Pressure Control (PC) Solenoid Valve

The PCM output signal to the PC solenoid valve increases the operating range of torque signal
fluid pressure in manual second. This provides the increased line pressure for the additional
torque requirements during the engine compression braking and increased engine loads.

IMPORTANT: Some vehicles in Manual Second Gear, at a stop, will start out in

1st gear, while others will have a second gear start. Refer to
Vehicle Owners Manual.

2007 Hummer H3

2007 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - H3

Fig. 496: Manual Second Gear Hydraulic Circuit Diagram
Courtesy of GENERAL MOTORS CORP.

MANUAL FIRST GEAR

A manual 2-1 downshift can be accomplished by moving the gear selector lever into the manual
first (1) position when the transmission is operating in second gear. The downshift to first gear is
controlled electronically by the PCM. The PCM will not energize the 1-2 shift solenoid valve to
initiate the downshift until the vehicle speed is below approximately 48 to 56 km/h (30 to 35
mph). Above this speed, the transmission operates in a manual first-second gear state. The
following text explains the manual 2-1 downshift.

Manual Valve

The selector lever moves the manual shaft and the manual valve into the manual first (1) position.
This allows the line pressure to enter the Lo fluid circuit.

Transmission Fluid Pressure (TFP) Manual Valve Position Switch Assembly

Lo fluid is routed to the TFP manual valve position switch where it closes the normally open lo
pressure switch. The addition of the lo pressure switch being closed signals to the PCM that
manual first is selected.

2007 Hummer H3

2007 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - H3