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