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36-1
TRANSFER CASE CONTROL
LT BLU
0.5
BRN
0.5
BLK
0.8
TRANSFER
CASE
SHIFT
CONTROL
MODULE
(4WD)
Connector
FRONT AXLE ACTUATOR
Connector
B
D
A
D6
C3
FUSE
BLOCK-
UNDERHOOD
Connector
F1
G107
(4.2L)
(5.3L)
See Ground
Distribution,
page 14-2.
E11
C2
E4
B11
A2
Axle
actuator
signal
B6
Axle
switch
signal
C2
C1
B1
Rear
high
signal
B2
Rear
low
signal
A2
Front
high
signal
A1
Front
low
signal
C2
F3
C3
C1
FUSE
BLOCK-
UNDERHOOD
Connector
M
Electronics
C
LSD
BLK
0.5
BLK
0.5
See Ground
Distribution,
page 14-2.
1
2
BLK/
WHT
0.5
BRN
0.5
BLK/
WHT
0.5
LT BLU
0.5
PROPSHAFT SPEED
SENSOR-REAR
TRANSFER CASE
Connector
1
2
PROPSHAFT SPEED
SENSOR-FRONT
TRANSFER CASE
Connector
LT BLU
0.35
LT BLU
0.35
DK GRN
0.35
DK GRN
0.35
YEL
0.35
YEL
0.35
PPL
0.35
PPL
0.35
C101
Connector
B9
B8
B4
B3
B2
Twisted
Twisted
Circuit Schematic
36-2
TRANSFER CASE CONTROL
RED
2
GRY
0.35
GRY/BLK
0.35
ATC
Fuse 8
25A
HOT AT ALL TIMES
FUSE
BLOCK-
UNDER-
HOOD
Connector
C2
A11
ORN
2
TRANSFER
CASE
Connector
D
B2
D
A
A1
B5
B
POWERTRAIN
CONTROL
MODULE
(PCM)
(4.2L)
(5.3L)
Connector 4.2L
Connector 5.3L
C1*
C2**
*4
**16
4WD
Low
signal
SP201
F
G201
Data Lines
BLK
2
See Ground
Distribution,
page 14-5.
TRANSFER
CASE
SHIFT
CONTROL
MODULE
(4WD)
Connector
C3
C3
E5
4WD
low
signal
Class 2
serial
data
DK GRN/WHT
0.35
12V
IPC class 2
serial data
B1
INSTRUMENT
PANEL
CLUSTER
(IPC)
Connector
Battery
positive
voltage
ORN
1
Lock
solenoid
control
C1
TAN
1
M
E
BLK
2
C
Motor
control A
Motor
control B
Motor
C101
Connector
B1
A7
Low
reference
B6
Encoder
signal
A8
5 volt
reference
A8
A2
A1
B6
A5
A
B
C
G
LT GRN/BLK
0.35
BRN/WHT
0.35
BLK/WHT
0.35
RED
2
TAN
1
BLK
2
LT GRN/BLK
0.35
BRN/WHT
0.35
BLK/WHT
0.35
ORN
1
Signal
Encoder
Brake
control
C1
C2
C3
Service
4WD/
AWD
F
Logic
C107
Connector
D7
GRY/BLK
0.35
Ground
5.3L
* 4.2L
** 5.3L
Circuit Schematic
36-3
TRANSFER CASE CONTROL
120Ć3
Transfer Case Shift Control Module
The transfer case shift control module uses the VIN
information for calculations that are required for the
different calibrations used based on axle ratio,
transmission, tire size, and engine. The system does
not know which calibration to use without this
information. When the vehicle is in the AWD mode, the
transfer case shift control module monitors the speed of
the front and rear propshafts in order to detect wheel
slippage. When wheel slippage is detected, the module
applies a clutch pack contained in side the transfer
case. This clutch pack is used to lock-in and apply the
front propshaft, transferring torque to the front wheels.
The clutch pack is applied by a motor/encoder
assembly. When slip is no longer detected by the
transfer case shift control module, the clutch is no
longer applied.
Transfer Case Motor/Encoder
The transfer case Motor/Encoder consists of a
permanent magnet (PM) DC motor and gear reduction
assembly. It is located on the left hand side (drivers
side) of the transfer case. When activated it turns the
sector shaft of the transfer case (clockwise or counter
clockwise)
to
shift
the
transfer
case.
The
Motor/Encoder is controlled with a pulse width
modulated (PWM) signal by the transfer case shift
control module. This circuit consists of a driver on both
the Motor A and Motor B circuits. The encoder motor is
bi-directional to allow the motor to shift the transfer case
from 2HI or 4HI to NEUTRAL and 4LO positions.
Transfer Case Encoder
The encoder is mounted to the transfer case
motor/encoder assembly and is replaced as an
assembly. The encoder converts the sector shaft
position (representing a mode or range) into an
electrical signal input to the transfer case shift control
module. The module can detect what position the
transfer case is in by monitoring the voltage returned on
the encoder signal circuit. This voltage translates into
AUTO, 2H, 4H, NEUTRAL, and 4L or in transition
between gears.
Transfer Case Motor Lock
The transfer case motor lock is used to provide a 2H,
4H, and 4L lock-up feature. When the lock circuit is
energized, the transfer case encoder motor is allowed
to turn. When the transfer case is placed 2H, 4H, or 4L
the motor lock circuit is de-energized and the lock is
applied. This assures that the transfer case remains in
the current gear position until a new gear position is
requested. When AUTO is selected the motor lock
remains applied until an adaptive mode (torque is
applied to the front propshaft) is required. During an
adaptive mode the motor lock circuit is energized and
the motor lock is released, enabling the encoder motor
to turn and apply or release torque at the front
propshaft.
Transfer Case Speed Sensors
There are three speed sensors on the automatic
transfer case (ATC), two on the rear output shaft and
one on the front output shaft. Each speed sensor is a
permanent magnet (PM) generator. The PM generator
produces a pulsing AC voltage. The AC voltage level
and number of pulses increases as speed increases.
Vehicle Speed Sensor
One of the two on the rear output shaft is the vehicle
speed sensor (VSS) input to the powertrain control
module (PCM). The PCM sends this information to the
transfer case shift control module via the Class 2 Serial
Data bus.
Rear Propshaft Speed Sensor
The transfer case shift control module converts the
pulsating AC voltage from the rear transfer case speed
sensor to a rear propshaft speed in RPM to be used for
calculations. The rear propshaft speed can be
displayed with a scan tool.
Front Propshaft Speed Sensor
The transfer case shift control module converts the
pulsating AC voltage from the front transfer case speed
sensor to front propshaft speed in RPM to be used for
calculations, and to monitor the difference between the
front and rear sensor speed. It is also used in the AUTO
(Adapt) mode of operation to determine the amount of
slip and the percent of torque to apply to the front axle.
The front propshaft speed can be displayed with a scan
tool.
SERVICE 4WD indicator
The SERVICE 4WD indicator is an integral part of the
cluster and cannot be serviced separately. This lamp is
used to inform the driver of the vehicle that a transfer
case system malfunction. The SERVICE 4WD indicator
is controlled by the transfer case shift control module
via Class 2.
Circuit Operation
36-4
TRANSFER CASE CONTROL
(Refer to Section 201 for photographs.)
Component
Photo No.
Body Control Module
(BCM)
On Rear Fuse Block, under left rear seat
53
. . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Front Axle Actuator
Lower right front of engine (on oil pan)
39
. . . . . . . . . .
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Fuse Block-Rear
Under the left rear seat
52
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Fuse Block-Underhood
Left side of engine compartment
3
. . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Instrument Panel Cluster
(IPC)
On the left side of the IP, above the steering column
59
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Powertrain Control Module
(PCM) (4.2L)
Left front of engine
5
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Powertrain Control Module
(PCM) (5.3L)
Left front of engine compartment
25
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Propshaft Speed Sensor-
Front Transfer Case
Left rear of transfer case
44
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Propshaft Speed Sensor-
Rear Transfer Case
Right rear of transfer case
43
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SP201
Near right front of lower console
80
. . . . . . . . . . . . . . . . . . . . .
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Transfer Case
On the rear of the transmission
44
. . . . . . . . . . . . . .
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Transfer Case Shift Control
Module (4WD)
Behind the left lower I/P
58
. . . . . . . . . . . .
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Transfer Case Shift Control
Switch
In lower center of the I/P
73
. . . . . . . . . . . . . . . . . . .
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Connector
C101 (38-BLK)
Left side of engine compartment
3
. . . . . . . . . . . . . .
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C107 (5.3L) (38-BLK)
Left rear of engine compartment
18
. . . . . . . .
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Ground
G102
Left side of engine compartment
4
. . . . . . . . . . . . . . . . . . . . . .
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G107 (4.2L)
Lower left side of engine
37
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G107 (5.3L)
Lower left side of engine
38
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G201
Near right front of lower console
80
. . . . . . . . . . . . . . . . . . . . . .
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Component Location Index
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