DaimlerChrysler LH New Yorker 1994, Электронное руководство по обслуживанию

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Control (Isolation) valves. The Traction Control (Iso-
lation) 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 re-
lease 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 requires.
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 pis-
ton pump. The motor shaft inside the pump is de-
signed 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
hydraulic tube. The (CAB) monitors the fluid level via
the fluid level switch (FLS2). When the reservoir is
properly 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.
PROPORTIONING VALVES
Two Proportioning Valves (Fig. 2 and 3) are used in
the system, one for each rear brake hydraulic circuit.
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). Replacement of
the proportioning valves will be covered later in this
section of the service manual.
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 sensor
(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 sensors. All wheel
speed sensors have a resistance between 950 and
1250 ohms.
The four wheel speed sensors are serviced individu-
ally. The front tonewheels are serviced as an assem-
bly with the outer C.V. Joint Housing. The rear tone-
wheels are serviced as an assembly with the rotor
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
accurate 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 pro-
Fig. 2 Hydraulic Control Unit Component Locations
Fig. 3 Anti-Lock Proportioning Valve Identification
ANTI-LOCK BRAKE SYSTEM 5 - 81