Hummer H1 (2006+). Manual - part 191

5-4

Transmission/Transfer Case

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REMOTE OIL COOLER PROVISION

The oil cooler lines are located on the right side of the converter housing near the converter housing/main housing split line. The
cooler lines go out of the transmission to the transmission cooler bypass valve located on the passenger side frame rail below the
engine mount bracket. From the transmission cooler bypass valve the lines go to the remote oil cooler located in the cool pack.
Heat is transferred from the transmission fluid to air.

TRANSMISSION COOLER BYPASS VALVE

The transmission cooler bypass valve is located on the passenger side frame rail below the engine mount bracket. The transmission
cooler bypass valve directs the cooler fluid back to the transmission until it reaches 150°F. By 180°F the valve is fully open and the
fluid is directed to the oil cooler. 

FILL TUBE/DIPSTICK PROVISION

All 1000 Series models have a fill tube/dipstick provision on both sides of the transmission. The fill tube and dipstick are located
on the passenger side. A plug is installed in the unused location on the driver side.

PARK PAWL

All 1000 Series transmissions have a PARK pawl. The internal parking pawl is engaged by selection of the PARK position on the
shift selector.

PTO PROVISION

Some 1000 Series transmissions have a provision to mount and drive a power takeoff (PTO) unit on the left and/or right side of the
transmission housing. The H1 transmission does not have this feature. 

TOW/HAUL MODE

Tow/Haul mode significantly changes the transmission shift pattern to reduce shift cycling and to deliver better performance, con-
trol, and cooling when towing or hauling heavy loads. For instance:

• Upshift points are raised at light to mid throttle position to use more of the available engine power for acceleration. Down-

shift points are raised to enhance engine braking to help slow the vehicle. 

• During deceleration, the torque converter clutch (TCC) remains applied at closed throttle at lower speeds to significantly im-

prove the effect of engine braking. 

• During acceleration, the TCC is applied in 2nd range and remains applied in 3rd, 4th, and 5th. This improves the drivetrain 

efficiency and significantly lowers transmission sump temperature when towing heavy loads. In Normal mode, the TCC 
generally applies only in higher ranges and is dependent on throttle position. 

• Tow/haul is designed to be most effective when the vehicle and trailer combined weight is at least 75 percent of the gross 

combined weight rating (GCWR) of the vehicle. 

• Operation of tow/haul in a lightly loaded or non-loaded vehicle will not cause damage. However, there is no benefit to the 

selection of tow/haul when the vehicle is unloaded. This situation will cause a firm shift. The tow/haul switch is not a perfor-
mance switch. 

• Selection of tow/haul when unloaded may result in unpleasant engine and transmission driving characteristics and reduced 

fuel economy. Tow/haul is recommended only when pulling a heavy trailer or a large or heavy load. 

Activation 

• Tow/Haul is selected or de-selected via a switch on the center console. The switch will illuminate to indicate that tow/haul 

has been selected. 

• Tow/Haul must be selected again, every time the vehicle is started, if desired. 

ADAPT FUNCTION

The transmission control module (TCM) produces excellent shift quality by applying closed loop control that constantly adjusts
shift characteristics for changes in operating conditions. These adjustments are based on vehicle conditions, such as grade, load,
and engine power.

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The learning process of comparing and adjusting shift parameters is referred to as adaptive control. The TCM constantly monitors
operating conditions, such as battery voltage and transmission sump temperature, and adjusts shift parameters accordingly. After a
shift is completed, the TCM compares the shift to a target shift profile in the TCM calibration and makes adjustments before the
next shift of the same kind is made.

TRANSMISSION GEAR RATIOS

Transmission gear ratios are:

TRANSMISSION IDENTIFICATION

An I.D. plate is attached to the passenger side of each Allison Transmission (Figure  5-1). The plate contains the model, date of
manufacture, serial number, engineering feature configuration, transmission identification, and the engineering group (Figure

5-2).

Figure 5-1:   Transmission I.D. Plate location 

First gear 

3.10:1

Second gear

1.81:1

Third gear 

1.41:1

Fourth gear

1.00:1

Fifth gear

0.71:1

Reverse 4.49:1

TRANSMISSION

I.D. PLATE

5-6

Transmission/Transfer Case

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Figure 5-2:   Transmission Identification (example plate)

TRANSMISSION CONTROL MODULE

A microcomputer controls the transmission by receiving and processing signals from various switches and sensors. The microcom-
puter determines shift sequences, shift timing, and clutch apply and release characteristics. The microcomputer is an independent
controller and is referred to as a transmission control module (TCM). The TCM has a 12 volt configuration to match the configura-
tion of the vehicle electrical system. The pressure switch manifold (PSM) and the park/neutral position (PNP) switch provide oper-
ator input to the TCM. Other data sent to the TCM include throttle position, engine, turbine, and output speeds, and sump
temperature. An active special function, such as anti-lock brakes, is also an input to the TCM. The TCM processes this data to de-
termine proper shift points, to monitor the current range, to perform ratio tests, and to compile diagnostic data. The TCM is pro-
grammed to protect the transmission and other vehicle driveline components by inhibiting actions, such as full-throttle
NEUTRAL-to-range shifts and high speed direction changes. The TCM determines if a system malfunction exists and stores diag-
nostic codes related to the malfunction. The codes, accessed by the service technician, are used in diagnosing persistent or intermit-
tent trouble in the system.

THROTTLE POSITION/TORQUE MANAGEMENT

The TCM receives input on throttle position/torque management, from a signal transmitted by the engine electronic controls. The
engine electronic controls communicate directly to the transmission electronic controls over a serial communication interface (SCI)
data link. The transmission TCM must be calibrated to receive these signals.

SPEED SENSORS

There are three speed sensors typically required for use with the 1000 Series transmissions (Figure  5-3). They include the input
speed sensor (TIS), the turbine speed sensor, and the output speed sensor (TOS). The speed sensors provide RPM information to
the TCM. The speed ratios between the various sensors allow the TCM to determine the transmission operating range. Speed sen-
sor information is also used to control the timing of clutch apply pressures, resulting in the best possible shift quality. Hydraulic
conditions are detected by comparing the speed sensor information, for the current range, to the range of the speed sensor informa-
tion stored in TCM memory. The speed sensors are variable reluctance devices that convert mechanical motion to an AC voltage.
Each sensor consists of a wire coil wrapped around a pole piece that is adjacent to a permanent magnet. These elements are con-
tained in a housing that is mounted adjacent to a rotating ferrous member.

VEHICLE SPEED SENSOR (VSS)

The vehicle speed sensor is located on the transfer case (Figure  5-3). Vehicle speed sensor information is used to determine vehi-
cle speed. The speed sensor is a variable reluctance device that converts mechanical motion to an AC voltage. The sensor consists
of a wire coil wrapped around a pole piece that is adjacent to a permanent magnet. These elements are contained in a housing that
is mounted adjacent to a rotating ferrous member. The signal is sent to the ECM then on to the speedo/tach module.

MODEL (SERIES)

DATE OF MANUFACTURE

SERIAL NUMBER

ENGINEERING

FEATURE CONFIGURATION

TRANSMISSION

IDENTIFICATION

ENGINEERING

GROUP

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Figure 5-3:    Speed Sensors

NEUTRAL START BACK UP (NSBU) SWITCH 

The vehicle is equipped with a console style shift selector. In addition to the console shift selector provided for the operator, an-
other component associated with the shift selector is the neutral start back up (NSBU) switch mounted on the selector shaft of the
transmission. The NSBU switch transmits selector position information to the TCM. The NSBU switch mounts directly onto the
transmission housing from the outside and detects the angular position of the shift selector shaft. this position is communicated to
the TCM so that certain vehicle control functions can be coordinated with the position of the shift controls. The NSBU switch has
redundant circuitry to alert the TCM in the event of a single wire or switch failure. The neutral signal output of the NSBU switch is
used as confirmation that the transmission is in neutral before the engine starter is engaged. The NSBU switch is interfaced to the
starter circuit. The reverse signal is used for back up lights, auto dimming mirror defeat and may be used for back up warning de-
vices.

INTERNAL TRANSMISSION COMPONENTS

Several components of the 1000 Series electrical control system are located within the transmission, as part of the main control
valve body. These components include three types of solenoids for controlling the hydraulic action of the valves, the pressure
switch manifold and an internal wiring harness that links the internal components with the TCM.

TRANSMISSION INPUT

SPEED SENSOR (TIS)

TRANSMISSION OUTPUT

SPEED SENSOR (TOS)

TURBINE SPEED

SENSOR

VEHICLE SPEED

SENSOR (VSS)