Chrysler PT Cruiser 2001 Service Manual Supplement page 1961

GENERAL INFORMATION
3.1.6 HYDRAULIC CONTROL UNIT
The hydraulic control unit (HCU) contains the
valve block assembly, two accumulators, and the
pump/motor assembly.
Valve Block Assembly: The valve block assem-
bly contains a total of 12 valves; 10 solenoid valves
with four inlet valves and four outlet valves, and
two traction control valves and two hydraulic shut-
tle 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 channel. If a wheel locks, the inlet
valve is closed to prevent any 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 (prop-
er slip ratio), both valves will close to hold the
pressure constant. The valves are also cycled during
a traction control event.
Pump/Motor Assembly: The pump/motor as-
sembly provides the extra amount of fluid needed
during antilock braking. The pump is supplied fluid
that is released to the accumulators when the outlet
valve is opened during an antilock stop. The pump
is also used to drain the accumulator circuits after
the antilock stop is complete. The pump is operated
by an integral electric motor. This DC-type motor is
controlled by the CAB. The CAB turns on the motor
when an antilock stop is detected. The pump con-
tinues to run during the antilock stop and is turned
off approximately 3-5 seconds after the stop is
complete. The pump mechanism consists of two
opposing pistons operated by an eccentric cam. One
piston supplies the primary hydraulic circuit. The
opposing piston supplies the secondary hydraulic
circuit. In operation, one piston draws fluid from
the accumulators. The opposing piston pumps fluid
to the valve body solenoids. The CAB monitors the
pump/motor operation internally.
Accumulators: The 3.0mm accumulators pro-
vide temporary fluid storage during an antilock
stop and are drained by the pump/motor.
3.1.7 SENSORS
Wheel Speed Sensors and Tone Wheels: One
Wheel Speed Sensor (WSS) is located at each wheel
and sends a small digital signal to the control
module (CAB). The CAB sends 12 volts down to the
sensor. The sensor has an internal magneto resis-
tance bridge that alters the voltage and amperage
of the signal circuit. This voltage and amperage is
changed by magnetic induction when a toothed
sensor ring (tone wheel) passes by a stationary
magnetic sensor (wheel speed sensor). The CAB
measures the voltage and amperage of the digital
signals for each wheel.
The front wheel sensor is attached to a boss in the
steering knuckle. The tone wheel is an integral part
of the front axle shaft. The rear speed sensor is
mounted in the caliper adapter plate and the rear
tone wheel is an integral part of the rear rotor hub.
• The wheel speed sensor air gap is NOT adjust-
able.
• Wheel speed sensors cannot be checked for resis-
tance to determine if they are ok.
Correct antilock system operation is dependent
on wheel speed signals from the wheel speed sen-
sors. The vehicle's wheels and tires should all be the
same size and type to generate accurate signals. In
addition, the tires should be inflated to the recom-
mended pressures for optimum system operation.
Variations in wheel and tire size or significant
variations in inflation pressure can produce inaccu-
rate wheel speed signals; however the system will
continue to function when using the mini-spare.
3.2 ABS DIAGNOSTIC TROUBLE CODES
The Teves Mark 20 Antilock Brake System (ABS)
module may report any of the following diagnostic
trouble codes:
• CAB Power Feed Circuit
•
Cluster Fault
• Controller Failure
• Incorrect Tone Wheel
• Left Front Sensor Circuit Failure
•
Left Front Sensor Signal Failure
• Left Rear Sensor Circuit Failure
• Left Rear Sensor Signal Failure
• PCI Bus Communication
•
Pump Motor Circuit Not Working Properly
• Right Front Sensor Circuit Failure
• Right Front Sensor Signal Failure
• Right Rear Sensor Circuit Failure
•
Right Rear Sensor Signal Failure
• System Overvoltage
• System Undervoltage
Diagnostic trouble codes are retained in memory
until erased using the DRBIII , or automatically
erased after 255 key cycles or 3500 miles.
3.2.1 SYSTEM INITIALIZATION
System initialization starts when the key is
turned to ''run''. At this point, the CAB performs a
complete self-check of all electrical components in
the antilock brake systems. The ABS, TRAC OFF,
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