Hummer H3. Manual — part 1696

cam (8) moves the lockup mode shift fork rearward along with the lockup shift collar assembly
(2). The lockup shift assembly sleeve (2) locks the mainshaft (1) to the drive sprocket (3). Torque
is sent by the chain (6) to the front output shaft (7) and to the front axle. The torque distribution
in this mode is now determined by vehicle dynamic conditions and weight distribution. The
planetary differential is not operating and both the front and rear propeller shafts are being driven
at equal RPM, therefore giving a 4 high lock mode. This mode should only be used for extra
traction during off road use. Using this mode on dry pavement causes tire scuffing.

4LO Lock Mode Power Flow

Fig. 150: 4LO Lock Mode Power Flow Diagram
Courtesy of GENERAL MOTORS CORP.

When the BW 4493, shown or the BW 4494, shown in inset, shifts the transfer case to the 4LO
Lock mode, it commands the encoder motor (7) to turn the shift cam shaft (8), to rotate the shift
cam (9). The range cam profile on the shift cam (9) moves the high/range shift fork (10) and the
high/low range sleeve (4) rearward to the 4LO Lock range position. The high/low range sleeve
(4) outer teeth disengage from the input shaft (1) high-speed teeth. The high/low range sleeve (4)

2007 Hummer H3

2007 TRANSMISSION Transfer Case - BW 4493/4494 - H3

outer teeth then engage in the high/low planetary carrier teeth (11). The power flow is now from
planetary teeth on the input shaft (1) to the planetary gears (2) in the carrier. Rotating the
planetary gears, which are engaged in the ring gear (3), rotates the planetary carrier. The
planetary carrier delivers the power to the high/low range sleeve (4). The high/low range sleeve
(4) then drives the mainshaft (5), providing a 2.64:1 reduction to the speed of the mainshaft (5).
When in the 4LO Lock position, the lockup mode shift fork and lockup shift assembly (6)
engages in the same way as in the 4HI Lock mode.

NEUTRAL Mode Power Flow

When the BW 4493/4494 shifts to the NEUTRAL position, the high/low range sleeve is centered
between the input shaft and the high/low planetary carrier. The high/low range sleeve is not
engaged with either the input shaft or the high/low planetary carrier teeth. The planetary
differential is in the AWD mode.

Transfer Case Electrical Components

View the list of major electrical components that make up the full-time 4 wheel drive transfer
case (FT4WD) system below.

Service 4WD Message

The SERVICE 4WD message is displayed on the driver information center, which is an integral
part of the cluster and cannot be serviced separately. This message is used to inform the driver of
malfunctions within the FT4WD transfer case system. The SERVICE 4WD message is controlled
by the transfer case shift control module via a Class 2 message.

Transfer Case Encoder

The encoder is mounted to the transfer case encoder motor assembly and is replaced only as an
assembly. The encoder converts the shift detent lever shaft position, representing a mode/range
into electrical signal inputs to the transfer case shift control module. The module detects what
position the transfer case is in by monitoring the 4 encoder channels, P, B, A and C. These inputs
translate into 4HI, 4HI Lock, 4LO Lock and NEUTRAL or whether the motor is still in transition
between gears.

The transfer case encoder channel circuits may be monitored using a scan tool.

Transfer Case Encoder Motor

2007 Hummer H3

2007 TRANSMISSION Transfer Case - BW 4493/4494 - H3

Fig. 151: Transfer Case Motor/Encoder Replacement
Courtesy of GENERAL MOTORS CORP.

The transfer case encoder motor consists of a permanent magnet DC motor and gear reduction
assembly. It is located on the left hand side of the transfer case. When activated, it turns the shift
detent lever shaft of the transfer case clockwise or counterclockwise, to shift the transfer case by
moving the shift forks and collar assemblies inside the transfer case. The encoder motor is
controlled through a 12-volt circuit provided by the transfer case shift control module. This
circuit consists of a driver on both the Motor Control A and Motor Control B circuits. The
encoder motor is bi-directional to allow the motor to shift the transfer case from 4HI or 4HI Lock
to NEUTRAL and 4LO Lock positions.

Both the motor control drivers and motor control return drivers can be turned on using a scan
tool. You may also monitor Motor Control A and B circuits using a scan tool.

Transfer Case Shift Control Module

2007 Hummer H3

2007 TRANSMISSION Transfer Case - BW 4493/4494 - H3

Fig. 152: Transfer Case Shift Control Module
Courtesy of GENERAL MOTORS CORP.

The transfer case shift control module uses the VIN information for calculations that are required
for the different calibrations used base on axle ratio, transmission, tire size and engine. The
system does not know which calibration to use without this information. This information is
provided to the transfer case shift control module via Class 2 data bus from the powertrain
control module (PCM). The transfer case shift control module monitors vehicle speed via the
Class 2 data bus from the PCM as well as controlling the operation of the transfer case encoder
motor assembly.

SPECIAL TOOLS AND EQUIPMENT

SPECIAL TOOLS

Special Tools

Illustration

Tool Number/Description

DT-47847

2007 Hummer H3

2007 TRANSMISSION Transfer Case - BW 4493/4494 - H3