Hummer H2. Manual — part 775

Anti-lock Brake System

When wheel slip is detected during a brake application, the ABS enters anti-lock mode. During anti-lock
braking, hydraulic pressure in the individual wheel circuits is controlled to prevent any wheel from slipping. A
separate hydraulic line and specific solenoid valves are provided for each wheel. The ABS can decrease, hold,
or increase hydraulic pressure to each wheel brake. The ABS cannot, however, increase hydraulic pressure
above the amount which is transmitted by the master cylinder during braking.

During anti-lock braking, a series of rapid pulsations is felt in the brake pedal. These pulsations are caused by
the rapid changes in position of the individual solenoid valves as the EBCM responds to wheel speed sensor
inputs and attempts to prevent wheel slip. These pedal pulsations are present only during anti-lock braking and
stop when normal braking is resumed or when the vehicle comes to a stop. A ticking or popping noise may also
be heard as the solenoid valves cycle rapidly. During anti-lock braking on dry pavement, intermittent chirping
noises may be heard as the tires approach slipping. These noises and pedal pulsations are considered normal
during anti-lock operation.

Vehicles equipped with ABS may be stopped by applying normal force to the brake pedal. Brake pedal
operation during normal braking is no different than that of previous non-ABS systems. Maintaining a constant
force on the brake pedal provides the shortest stopping distance while maintaining vehicle stability.

Pressure Hold

The EBCM closes the inlet valve and keeps the outlet valve closed in order to isolate the system when wheel
slip occurs. This holds the pressure steady on the brake so that the hydraulic pressure does not increase or
decrease.

Pressure Decrease

The EBCM decreases the pressure to individual wheels during a deceleration when wheel slip occurs. The inlet
valve is closed and the outlet valve is opened. The excess fluid is stored in the accumulator until the return
pump can return the fluid to the master cylinder.

Pressure Increase

The EBCM increases the pressure to individual wheels during a deceleration in order to reduce the speed of the
wheel. The inlet valve is opened and the outlet valve is closed. The increased pressure is delivered from the
master cylinder.

Dynamic Rear Proportioning (DRP)

The dynamic rear proportioning (DRP) is a control system that replaces the hydraulic proportioning function of
the mechanical proportioning valve in the base brake system. The DRP control system is part of the operation
software in the EBCM. The DRP uses active control with existing ABS in order to regulate the vehicle's rear
brake pressure.

The red brake warning indicator is illuminated when the dynamic rear proportioning function is disabled.

2004 Hummer H2

2004 BRAKES Anti-Lock Brake System - Hummer H2

Traction Control (TCS) NW9

The primary function of the Traction Control System (TCS) is to optimize vehicle performance with varying
vehicle load and changing road conditions by controlling wheel slip at the driven wheels during an acceleration
maneuver. The wheel slip is controlled by actively applying braking force. This modulation is applied and occur
under all throttle input conditions where the difference between wheel speed' and vehicle speed indicate a loss
of longitudinal traction.

TCS operation for each mode of driveline operation include the following. When high range is selected for the
transfer case, the system controls wheel slip in the order of stability and acceleration. When low range is
selected for the transfer case, the system controls wheel slip in the order of acceleration and stability.

A traction mode switch (TC2) is included to improve traction system performance on loose surfaces. The mode
switch will have a momentary action and resets when the switch is pressed again or the ignition is cycled. The
switch will have two states, one state is Road, and the other state is Loose Surface. When the switch is in the
Road mode, the traction system will preform at its maximum, and in the loose surface mode will be adjusted for
road conditions.

The braking is accomplished by closing the TCS Master Cylinder Isolating Valve, this isolates the master
cylinder from the rest of the system. The TCS Prime valve opens to allow the pump to get brake fluid to build
pressure for braking. The drive wheel circuit solenoids are energized as needed to allow for pressure hold,
pressure increase, or pressure decrease.

ABS Indicator

The IPC illuminates the ABS indicator when the following occurs:

z

The electronic brake control module (EBCM) detects a malfunction with the anti-lock brake system. The
IPC receives a class 2 message from the EBCM requesting illumination.

z

The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for
approximately 3 seconds.

z

The IPC detects a loss of class 2 communications with the EBCM.

Brake System Indicator(s)

Brake Warning Indicator

The IPC illuminates the BRAKE indicator when the following occurs:

z

The IPC detects that the park brake switch is closed (park brake set).

z

The IPC detects a low brake fluid condition.

z

The IPC performs the displays test at the start of each ignition cycle.

z

The EBCM senses a base brake failure.

z

The IPC detects a loss of class 2 communications with the EBCM.

Traction Assist

2004 Hummer H2

2004 BRAKES Anti-Lock Brake System - Hummer H2

The IPC illuminates the traction assist indicator when the following occurs:

z

The electronic brake control module (EBCM) detects a malfunction with the anti-lock brake system. The
IPC receives a class 2 message from the EBCM requesting illumination.

z

The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for
approximately 3 seconds.

z

The IPC detects a loss of class 2 communications with the EBCM.

Loose Surface Switch LED

The EBCM illuminates the LED indicator, part of the TC2 switch, when the following occurs:

z

The EBCM performs the displays test at the start of each ignition cycle. The LED indicator illuminates
for approximately 3 seconds.

z

The EBCM flashes the Loose Surface Switch LED during the transition between modes. Once the
transition is complete, the EBCM does not flash the LED.

z

Entering Loose Surface Mode, the LED remains illuminated.

z

Entering normal Surface Mode, the LED remains off.

SPECIAL TOOLS AND EQUIPMENT

SPECIAL TOOLS

Special Tools

Illustration

Tool Number/Description

J 39200

Digital Multimeter

2004 Hummer H2

2004 BRAKES Anti-Lock Brake System - Hummer H2

J 39700

Universal Pinout Box

2004 Hummer H2

2004 BRAKES Anti-Lock Brake System - Hummer H2