Hummer H1 (2002+). Manual - part 51

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Transmission/Transfer Case 5-3

05745159

TRANSMISSION IDENTIFICATION

An I.D. plate is attached to the passenger side of each Hydra-
matic Transmission (Figure 5-2). The plate contains the model,
Hydra-matic type, model year, calendar year, and Julian calen-
dar date.

The I.D. plate information is required for correct service parts
ordering.

Figure 5-2: Transmission I.D. Plate Information

(Example Plate)

ELECTRONIC SHIFT CONTROL COMPONENTS

Upshifts and downshifts in overdrive and manual D ranges are
electronically controlled. Transmission electronic components
include (Figure 5-3):

• Automatic Transmission Fluid Temperature Sensor

• Automatic Transmission Fluid Pressure Manual Valve

Position switch

• Automatic Transmission Input (shaft) Speed Sensor

• Automatic Transmission Output(shaft) Speed Sensor

(Vehicle Speed Sensor)

• 1-2 and 2-3 shift solenoids

• Pressure Control Solenoid Valve

• Torque Converter Clutch Pulse Width Modulated Sole-

noid

• PCM (powertrain control module)

Additional inputs to the transmission PCM are provided by: the
engine coolant temperature sensor, Cruise Control, A/C re-
quest, electronic accelerator pedal, crankshaft position sensor,
and brake switch.

Adapt Function

The 4L80-E transmission uses a line pressure control system,
which has the ability to continuously adapt the system’s line
pressure. This compensates for normal wear and break in of the
following parts.

• The clutch fiber plates

• The seals

• The springs

The PCM maintains the following adapt parameters for the
transmission:

• Upshift Adapt - The PCM monitors the Automatic

Transmission Input (Shaft) Speed Sensor (A/T ISS) and
the Output or Vehicle Speed Sensor (VSS) during com-
manded shifts in order to determine if a shift is occur-
ring too fast or too slow. The PCM adjusts the signal to
the transmission pressure control solenoid valve in order
to maintain a set shift feel.

• Steady State Adapt - The PCM monitors the Automatic

Transmission Input (Shaft) Speed Sensor (A/T ISS) and
the Vehicle Speed Sensor (VSS) after a shift in order to
calculate the amount of slippage in that gear. The PCM
then adjusts the signal to the Transmission Pressure
Control Solenoid signal in order to maintain slippage
below a set amount.

Reset the Transmission Adapt functions when the transmission
is overhauled or replaced. To reset the Transmission Adapt
functions, use the Tech 1 Scan Tool.

TRANSMISSION

I.D. PLATE

JULIAN DATE

CALENDAR

YEAR

MODEL YEAR

(98 = 1998)

MODEL

HYDRA-MATIC

4L80-E/4L80-EHD

000

5-4

Transmission/Transfer Case

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Figure 5-3: Transmission Shift Control Components

TRANSMISSION FLUID PRESSURE MANUAL
VALVE POSITION SWITCH

The pressure switch assembly is mounted on the valve body. It
contains five pressure switches in circuit with the PCM
(Figure 5-4). The switches are used to signal the PCM which
gear range has been selected.

Each pressure switch is activated by fluid pressure
(Figure 5-5). Fluid flow through the manifold is controlled by
the valve body manual valve (Figure 5-6).

The five pressure switches are closed only when fluid pressure
is applied. Fluid flow into the switch cavity presses the dia-
phragm downward against the contact element and switch con-
tact (Figure 5-4). Once the switch closes, it completes the
ground circuit to the PCM through one of the connector pins
(Figure 5-4).

The hydraulic and electrical schematics in Figure 5-6 illustrate
switch activation and fluid flow in third gear. The Drive and
PRND 4/3 switches are pressurized closing the circuit to con-
nector pin C (Figure 5-4). This changes the digital logic at Pin
C to O and the logic at Pins A and B to 1 (Figure 5-6). The
PCM reads this as third gear.

Figure 5-4: Pressure Switch and Connector

Identification

FLUID

TEMPERATURE

SENSOR

INPUT

SPEED

SENSOR

CONVERTER

CLUTCH

SOLENOID

PRESSURE

CONTROL

SOLENOID

PRESSURE

SWITCH

ASSEMBLY

SHIFT

SOLENOIDS

REVERSE

SWITCH

PRND 4/3

SWITCH

LO (1-2)

SWITCH

THREE PIN

CONNECTOR

PRESSURE

SWITCH

ASSEMBLY

PRND 4

SWITCH

DRIVE

SWITCH

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Transmission/Transfer Case 5-5

05745159

Figure 5-5: Pressure Switch Actuation

Figure 5-6: Hydraulic/Electrical Circuitry for Pressure Switch Assembly (Third Gear Shown)

CONTACT

BODY

FLUID

O-RING

DIAPHRAGM

GROUND

CONTACT

ELEMENT

SWITCH

CONTACT

ELEMENT

SWITCH

CONTACT

GROUND

DIAPHRAGM

O-RING

FLUID

BODY

5-6

Transmission/Transfer Case

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AUTOMATIC TRANSMISSION INPUT (SHAFT)
SPEED SENSOR AND OUTPUT (SHAFT) SPEED
SENSOR (VEHICLE SPEED SENSOR)

The input and vehicle speed sensors are variable reluctance,
magnetic pickup units (Figure 5-7). They consist of a perma-
nent magnet surrounded by a wire coil. The sensors are
mounted in the driver side of the transmission case and the top
of the transfer case at the rear.

The vehicle speed sensor is positioned opposite the speedome-
ter tone wheel in the rear of the transfer case. The input sensor
is opposite the machined teeth on the forward clutch housing in
the transmission (Figure 5-7). The tone wheel and gear teeth
interrupt the sensor magnetic field as they rotate. This induces
an AC current in each sensor coil. The vehicle sensor provides
a voltage signal proportional to vehicle speed. The input sensor
signal indicates transmission shaft/turbine speed. Both sensor
signals are used by the PCM to determine shift speed, pattern,
and converter clutch apply.

Sensor signals reaching the PCM are converted to a square
wave form (Figure 5-7). The wave forms correspond to the
teeth on the speedometer tone wheel and forward clutch. The
increase in shaft speed will cause more teeth to interrupt the
sensor magnetic field in a given time. This is reflected in an in-
crease in the number of wave forms sent to the PCM. The wave
forms are compared to a fixed signal voltage in the PCM to de-
termine speeds.

Figure 5-7: Transmission Speed Sensor Signal Form

TRANSMISSION FLUID TEMPERATURE SENSOR

The fluid temperature sensor is mounted on the internal trans-
mission harness. Failure of the sensor constitutes wiring har-
ness replacement. It is a temperature sensitive resistor more
commonly known as a thermister (Figure 5-8). Low fluid tem-
perature produces high resistance. The PCM controls torque
converter clutch apply based on sensor input signals.

The PCM will not allow converter clutch apply when fluid
temperature is below 68°F (20°C). At higher fluid tempera-
tures, the PCM will apply or release the converter clutch as fol-
lows:

• Apply the clutch in second, third, fourth when fluid tem-

perature exceeds 250°F (122°C).

• Release the clutch and prevent apply in any gear range

when fluid temperature reaches or exceeds 300°F
(150°C).

• Prevent converter clutch apply and set a-fault code

when fluid temperature reaches 310°F (154°C).

Figure 5-8: Temperature Sensor

O-RING

ELECTRICAL

CONNECTOR

SPEED

SENSOR

MAGNETIC PICKUP

(MAGNET AND COIL)

LOW SPEED

HIGH SPEED

TIME

SIGNAL VOLTS

5.0

CONDITIONED SQUARE WAVE SIGNAL

FOWARD CLUTCH

GEAR TEETH OR

SPEEDOMETER

TONE WHEEL

SENSOR

ELEMENT

TEMPERATURE

SENSOR

16,000

133

-10°C
+16°F

110°C
230°F

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