Traction Control System; Hydraulic Circuits And Valve Operation; Hydraulic Shuttle Valves; Traction Control Function Lamps - Chrysler 2000 LHS Owner's Manual

5 - 60 BRAKES
DESCRIPTION AND OPERATION (Continued)
Fig. 5 Rear Wheel Speed Sensor
1 – PARKING BRAKE CABLE
2 – BACKING PLATE
3 – REAR WHEEL SPEED SENSOR
4 – REAR STRUT
OPERATION
The wheel speed sensor sends a small AC signal to
the CAB. This signal is generated by magnetic induc-
tion created when a toothed sensor ring (tone wheel)
passes the stationary magnetic wheel speed sensor.
The CAB converts the AC signal into a digital signal.
If a wheel locking tendency is detected by the CAB, it
will then modulate hydraulic pressure via the HCU
to prevent the wheel(s) from locking.
Correct ABS operation is dependent on accurate
wheel speed signals. The vehicle's tires and wheels
all must be the same size and type to generate accu-
rate signals. Variations in tire and wheel size can
produce inaccurate wheel speed signals.
Improper speed sensor-to-tone wheel clearance can
cause erratic speed sensor signals. The speed sensor
air gap is not adjustable, but should be checked when
applicable. Wheel speed sensor-to-tone wheel clear-
ance specifications can be found in the SPECIFICA-
TIONS section in this section of this service manual
group.

TRACTION CONTROL SYSTEM

DESCRIPTION
Traction control reduces wheel slip and maintains
traction at the driving wheels at speeds below 56 kph
(35 mph) when road surfaces are wet or snow cov-
ered. The traction control system reduces wheel slip
by braking the wheel that is losing traction.
OPERATION
The traction control system monitors wheel speed.
During acceleration, if the CAB detects front (drive)
wheel slip and the brakes are not applied, the system
enters traction control mode. Traction control opera-
tion proceeds in the following order:
(1) Close the normally open isolator valves.
(2) Start the pump/motor and supply volume and
pressure to the front (drive) hydraulic circuit. (The
pump/motor runs continuously during traction con-
trol operation.)
(3) Open and close the build and decay valves to
maintain minimum wheel slip and maximum trac-
tion.
The cycling of the build and decay valves during
traction control is similar to that during antilock
braking, except the valves work to control wheel spin
by applying the brakes, whereas the ABS function is
to control wheel skid by releasing the brakes.

HYDRAULIC SHUTTLE VALVES

Two hydraulic shuttle valves allow pressure and
volume to return to the master cylinder reservoir
when not consumed by the build and decay valves.
These valves are necessary because the pump/motor
supplies more volume than the system requires.
If the brakes are applied at anytime during a trac-
tion control cycle, the brake lamp switch triggers the
CAB to switch off traction control.

TRACTION CONTROL FUNCTION LAMPS

The traction control function lamp illuminates dur-
ing a traction control cycle, displaying TRAC ON.
The traction control system is enabled at each igni-
tion cycle. It may be turned off by depressing the
traction control switch button. The traction control
function lamp (TRAC OFF) illuminates immediately
upon depressing the button.
If the CAB calculates that the brake temperatures
are high, the traction control system becomes inoper-
ative until a time-out period has elapsed. During this
"thermo-protection mode," the traction control func-
tion lamp illuminates TRAC OFF; note that no trou-
ble code is registered.
In the event that a system fault occurs thus illu-
minating the amber ABS warning lamp, the TRAC
OFF lamp will also illuminate.

HYDRAULIC CIRCUITS AND VALVE OPERATION

The hydraulic fluid control valves control the flow
of pressurized brake fluid to the wheel brakes during
the different modes of ABS braking. The following
paragraphs explain how this works. For purposes of
explanation only, it is assumed that only the right
front wheel is experiencing antilock braking; the fol-
LH