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5 - 56
BRAKES
•
A
standard master cylinder and. vacuum power
brake booster are used for a l l applications.
ANTI-LOCK
ELECTRONIC
CONTROL
MODULE
The electronic module controls a l l phases of a n t i -
lock mode brake operation. The module is separate
from other electrical circuits i n t h e vehicle a n d oper-
ates independently.
The module is located on the passenger side cowl
panel under the dash (Fig. 2). The system h y d r a u l i c
valve, speed sensor a n d indicator lamps are a l l i n cir-
cuit w i t h the module. The module contains a micro-
processor t h a t operates
the system and performs
system diagnostic checks.
Speed sensor i n p u t s are continuiously monitored
and interpreted by t h e module. The module deter-
mines wheel speed and rate of deceleration
from
these inputs and activates t h e appropriate solenoid
i n t h e hydraulic valve w h e n necessary.
The module microprocessor also contains a self test
program. The p r o g r a m is activated w h e n the i g n i t i o n
switch is t u r n e d to the O n position. I n t h i s mode, the
module checks indicator l i g h t operation, the system
electrical circuits and t h e pressure l i m i t i n g valve so-
lenoids.
The brake w a r n i n g and anti-lock indicator lamps
are i l l u m i n a t e d for approximately t w o seconds dur-
i n g the system self test cycle.
Fig. 2 Anti-Lock Electronic Control Module
RWAL HYDRAULIC
VALVE
The h y d r a u l i c valve is a pressure c o n t r o l l i n g device
and is operated by the electronic module. The valve
controls f l u i d apply pressure to t h e r e a r brake u n i t s
d u r i n g a n t i - l o c k mode b r a k i n g (Fig. 3). The valve is
mounted on t h e d r i v e r side frame r a i l at the front of
the vehicle.
The valve contains a n accumulator, a n isolation
valve and a d u m p valve. The accumulator is operated
by f l u i d a n d s p r i n g pressure. The t w o valves are op-
erated by electrical solenoids. The solenoids are oper-
ated by t h e anti-lock control module.
The h y d r a u l i c valve components are inactive dur-
i n g periods o f n o r m a l b r a k i n g effort. The valve com-
ponents are activated only w h e n b r a k i n g effort a n d
rate of wheel slip and deceleration are h i g h ( a n t i -
lock mode).
D u r i n g n o r m a l b r a k i n g t h e valve allows free flow
of brake f l u i d to the rear b r a k e u n i t s . I n anti-lock
mode, t h e v a l v e w i l l decrease, h o l d or increase f l u i d
apply pressure as needed.
CONNECTOR
J9005-99
Fig. 3 RWAL Hydraulic Valve
SPEED SENSOR
AND EXITER
RING
A single pole, variable reluctance speed sensor is
used to t r a n s m i t speed a n d rate of deceleration i n -
puts to the control module (Fig. 4). The sensor is ac-
tuated by a n exiter r i n g on the differential case.
The sensor is mounted a t t h e top of the rear axle
housing d i r e c t l y over the gear-type exiter r i n g (Fig.
1). The exiter r i n g is pressed onto the differential
case next to t h e r i n g gear.
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