Jeep KJ Liberty 2005, Service Manual

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• integrated hydraulic control unit (HCU), 1 pump
motor.
•
4 wheel speed sensor/tone wheel assemblies
• ABS warning indicator
•
fuses and wiring harness
• fluid reservoir
• brake lamp switch
ABS With Traction Control
• ABM with Traction Control programming
•
HCU with four additional control valves.
• TCS Switch
•
TCS Indicator
3.3.1 ABS AND BRAKE WARNING
INDICATORS
The amber ABS warning indicator is located in
the instrument cluster. It is used to inform the
driver that the antilock function has been turned
off. The ABS warning indicator is controlled by the
ABM. The ABM controls the lamp with a command
over the PCI bus.
The ABS Warning Indicator will remain lit during
every key cycle until a circuit or component fault is
repaired and the ABM no longer detects the fault.
After repair of a sensor signal fault or a pump motor
fault, the ABM must sense all four wheels at 25
km/h (15 mph) before it will extinguish the ABS and
TCS Indicator.
The Instrument Cluster will illuminate the ABS
Warning Indicator if it loses communication with
the ABM.
The red BRAKE warning indicator is also located
in the instrument cluster. It can be activated in
several ways. Application of the parking brake or a
low fluid signal from the fluid level switch located in
the master cylinder reservoir will cause the indica-
tor to come on.
3.3.2 ANTI-LOCK BRAKE MODULE
The ABM is a microprocessor-based device that
monitors wheel speeds and controls the antilock
functions. The ABM contains two microprocessors
that receive identical sensor signals and then inde-
pendently process the information. The results are
then compared to make sure that they agree. Oth-
erwise, the ABM will turn off the antilock and turn
on the ABS amber warning indicator.
The primary functions of the ABM are to:
•
detect wheel locking tendencies
• control fluid pressure modulation to the brakes
during antilock stop
•
monitor the system for proper operation
• manage traction control functions
• provide communication to the DRBIII
t
while in
diagnostic mode
•
store diagnostic information in non-volatile mem-
ory
The ABM continuously monitors the speed of
each wheel. When a wheel locking tendency is
detected, the ABM will command the appropriate
valve to modulate brake fluid pressure in its hy-
draulic unit. Brake pedal position is maintained
during an antilock stop by being a closed system.
The ABM continues to control pressure in individ-
ual hydraulic circuits until a wheel locking ten-
dency is no longer present. The ABM turns on the
pump motor during an antilock stop.
The antilock brake system is constantly moni-
tored by the ABM for proper operation. If the ABM
detects a system malfunction, it can disable the
antilock system and turn on the ABS warning
indicator. If the antilock function is disabled, the
system will revert to standard base brake system
operation.
The ABM inputs include the following:
• diagnostic communication
•
four wheel speed sensors
• three power feeds: valve, pump, and microproces-
sor
•
brake lamp switch
• traction control switch
The ABM outputs include the following:
•
ABS warning indicator actuation
• 12 volts power to wheel speed sensors
• valve actuation
• diagnostic communication
• PCI bus communication
•
traction control lamp illumination
3.3.3 HYDRAULIC CONTROL UNIT
The hydraulic control unit (HCU) contains the
valve block assembly, and pump/motor assembly.
The HCU is attached to the ABM.
Valve Block Assembly: The valve block assem-
bly contains valves with four inlet valves and four
outlet valves. The inlet valves are spring-loaded in
the open position and the outlet valves are spring
loaded in the closed position. During an antilock
stop, these valves are cycled to maintain the proper
slip ratio for each wheel. If a wheel detects slip, the
inlet valve is closed to prevent and further pressure
increase. Then the outlet valve is opened to release
the pressure to the accumulators until the wheel is
no longer slipping. Once the wheel is no longer
slipping, the outlet valve is closed and the inlet
valve is opened to reapply pressure. If the wheel is
decelerating
within its predetermined limits
(proper slip ratio), the inlet valve will close to hold
2
GENERAL INFORMATION