Chrysler Concorde 1993 Service Manual page 175

Control (Isolation) valves and a pressure switch. The
valves are spring loaded in the open position. During
traction control operation the traction control valves
are closed by the (CAB). This hydraulically isolates the
front brake channels from the master cylinder, and the
rear brake channels. The (CAB) activates the
motor/pump by grounding the motor/pump relay coil.
By opening and closing the inlet and outlet valves the
(CAB) can apply and release the drive wheel calipers as
needed to control wheel spin. Two pressure relief
valves allow unused fluid volume/pressure to return to
the reservoir. The relief valves are needed because the
pump can supply more volume than the system re-
quires.
A bleeding procedure using the DRB II scan
tool must be used to remove air that has become
trapped in the H.C.U.
PUMP/MOTOR ASSEMBLY
The pump/motor assembly (Fig. 2) consists of an
electric motor with a rotation sensor and a dual piston
pump. The motor shaft inside the pump is designed as
a cam in order to drive both pistons. The rotation
sensor is an inductive pick-up used by the (CAB) to
monitor pump/motor operation.
FLUID RESERVOIR AND FLUID LEVEL SWITCH - FLS2
The fluid reservoir at the H.C.U. (Fig. 2) includes a
fluid level switch (FLS2). This reservoir is connected to
the master cylinder reservoir by a low pressure hy-
draulic tube. The (CAB) monitors the fluid level via the
fluid level switch (FLS2). When the reservoir is prop-
erly filled the fluid level switch is closed. If the fluid
level falls below an acceptable level, the fluid level
switch will open. When the (CAB) detects a low fluid
condition (FLS2 OPEN) it will inhibit the anti-lock and
traction control function, and turn on the ABS and
Traction Control
warning lamps.
Fig. 2 Hydraulic Control Unit Component Locations
ANTI-LOCK BRAKE SYSTEM
PROPORTIONING VALVES
Two Proportioning Valves (Fig. 2 and 3) are used
in the system, one for each rear brake hydraulic cir-
cuit. The Proportioning Valves function the same as
in a standard brake system. The Proportioning
Valves are located on the bottom of the (HCU) (Fig.
1). The proportioning valves are not serviceable but
are a replaceable component of the (HCU). Replace-
ment of the proportioning valves will be covered
later in this section of the service manual.
Fig. 3 Anti-Lock Proportioning Valve Identification
WHEEL SPEED SENSORS
One wheel speed sensor (WSS) is located at each
wheel (Fig. 4) and sends a small AC signal to the
control module (CAB). This voltage is generated by
magnetic induction when a toothed sensor ring (tone-
wheel) (Fig. 5) passes by a stationary magnetic sen-
sor (WSS). The (CAB) converts the AC signals into
digital signals for each wheel.
The front wheel sensor (Fig. 4) is attached to a boss
in the steering knuckle. The tonewheel is an integral
part of the front axle shaft (Fig. 5). The rear speed
sensor (Fig. 4) is mounted in the caliper adapter
plate and the rear tonewheel is an integral part of
the rear rotor hub (Fig. 5). The wheel speed sensor
air gap is NOT adjustable. The correct wheel speed
sensor air gap is from 0.52 to 1.64mm for the front
sensors, and from 0.45 to 1.21mm for the rear sen-
sors. All wheel speed sensors have a resistance be-
tween 950 and 1250 ohms.
The four wheel speed sensors are serviced individ-
ually. The front tonewheels are serviced as an assem-
bly with the outer C.V. Joint Housing. The rear
tonewheels are serviced as an assembly with the ro-
tor hub (Fig. 5).
Correct Anti-Lock and Traction Control system op-
eration is dependent on wheel speed signals from the
wheel speed sensors. The vehicles' wheels and tires
should all be the same size and type to generate ac-
curate signals. In addition, the tires should be in-
flated to the recommended pressures for optimum
system operation. Variations in wheel and tire size
or significant variations in inflation pressure can
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