Hummer H2. Manual - part 2703

Fig. 158: 4LO Lock Mode Power Flow 
Courtesy of GENERAL MOTORS CORP. 

When shifting the transfer case to the 4LO Lock mode, it commands the encoder motor (7) to turn the shift 
detent lever shaft (8), to rotate the shift detent lever cam (9). The range cam profile on the shift detent lever 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) 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 annulus 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 

Shifting 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 

 

2004 Hummer H2 

2004 DRIVELINE/AXLE Transfer Case - BW 4484 - Hummer H2

  

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 four 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 

 

2004 Hummer H2 

2004 DRIVELINE/AXLE Transfer Case - BW 4484 - Hummer H2

  

Fig. 159: Transfer Case Encoder Motor 
Courtesy of GENERAL MOTORS CORP. 

The transfer case encoder motor consists of a permanent magnet (PM) 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.

 

2004 Hummer H2 

2004 DRIVELINE/AXLE Transfer Case - BW 4484 - Hummer H2

  

Transfer Case Shift Control Module 

Fig. 160: 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 

 

2004 Hummer H2 

2004 DRIVELINE/AXLE Transfer Case - BW 4484 - Hummer H2