warning CHEVROLET DYNASTY 1993 Workshop Manual

DUAL FUNCTION PRESSURE SWITCH
REMOVE
WARNING: FAILURE TO DE-PRESSURIZE THE HY-
DRAULIC ACCUMULATOR PRIOR TO REMOVING
DUAL FUNCTION PRESSURE SWITCH. WILL RESULT
IN PERSONAL INJURY AND/OR DAMAGE TO
PAINTED SURFACES OF THE VEHICLE. CAUTION: THOROUGHLY CLEAN THE BOTTOM OF
THE HYDRAULIC ASSEMBLY IN THE AREA OF THE
DUAL FUNCTION PRESSURE SWITCH, BEFORE RE-
MOVING THE SWITCH FROM HYDRAULIC ASSEM-
BLY. USE MOPAR BRAKE PARTS CLEANER OR AN
EQUIVALENT. EXTREME CARE MUST BE USED SO
NO DIRT IS ALLOWED TO ENTER THE HYDRAULIC
ASSEMBLY THROUGH WHERE THE DUAL FUNC-
TION PRESSURE SWITCH IS MOUNTED. ANY DIRT
ENTERING HYDRAULIC ASSEMBLY MAY PLUG IN-
TERNAL PASSAGES CAUSING A HYDRAULIC AS-
SEMBLY FAILURE.
(1) Fully de-pressurize the hydraulic accumulator by
pumping brake pedal a minimum of 40 times. Use
procedure described in De-Pressurizing Hydraulic Ac-
cumulator listed earlier in this section. (2) Raise vehicle See Hoisting, Group 0.
(3) From under vehicle, disconnect wiring harness
connectors from dual function pressure switch and
boost pressure transducer (Fig. 9) on the bottom of
hydraulic assembly.
WARNING: WEAR EYE PROTECTION WHEN PER-
FORMING THE FOLLOWING PROCEDURE. SERIOUS
EYE INJURY CAN RESULT FROM BRAKE FLUID
CONTACTING THE EYES.
(4) Be sure that the hydraulic system is de-
pressurized. Remove the dual function pressure
switch from the hydraulic assembly using Socket,
Special Tool 6607 (Fig. 10). Access to the switch is from
under the vehicle using a long extension.
Fig. 6 Rear Wheel Speed Sensor Routing at Trailing Arm
Fig. 7 Removing Speed Sensor (Typical)
5 - 106 ANTI-LOCK 10 BRAKE SYSTEM Ä

CAUTION: Do not insert dual function pressure
switch into hydraulic assembly using the socket
and ratchet. Cross threading of the switch may oc-
cur. (1) Install the dual function pressure switch into
the hydraulic assembly by hand until the O-ring
seals are seated. (2) Using Socket, Special Tool 6607, (Fig. 10)
torque the dual function pressure switch into the hy-
draulic assembly to 12 N Im (9 ft. lbs.).
(3) Connect the wiring harness connectors (Fig. 9)
onto the dual function pressure switch and the boost
pressure transducer. Be sure the locking tabs on the
connectors are fully engaged on the switches. (4) Lower the vehicle.
(5) Turn the ignition switch to the on position and
let the system pressurize. Check for any leaks at the
dual function pressure switch. (6) Fully de-pressurize the hydraulic assembly a
second time. This will purge any air out that may
have entered hydraulic assembly when the switch
was removed. Turn the ignition switch to the on po-
sition and let the system pressurize again. (7) Road test vehicle to insure that the brake sys-
tem is performing correctly.
PRIMARY PRESSURE TRANSDUCER
REMOVE
WARNING: FAILURE TO FULLY DE-PRESSURIZE
THE HYDRAULIC BLADDER ACCUMULATOR PRIOR
TO REMOVING PRIMARY PRESSURE TRANS-
DUCER. WILL RESULT IN PERSONAL INJURY
AND/OR DAMAGE TO PAINTED SURFACES OF THE
VEHICLE.
To remove primary pressure transducer (Fig. 11),
from hydraulic assembly, removal of hydraulic as-
sembly from vehicle is notrequired.
(1) Fully de-pressurize the hydraulic accumulator
by pumping brake pedal a minimum of 40 times. Use
procedure described in De-Pressurizing Hydraulic Ac-
cumulator listed earlier in this section. (2) Remove as much brake fluid as possible from
the brake fluid reservoir, using a syringe or equiva-
lent method. (3) Using oil filter band wrench, Special Tool
C-4065 or equivalent, (Fig. 12) loosen bladder accu-
mulator. Then remove bladder accumulator and
brake fluid spray shield from hydraulic assembly. (4) Remove high pressure banjo fitting (Fig. 13)
from hydraulic assembly. (5) Using needle nose pliers, remove the 3 fluid
reservoir retaining pins from the hydraulic assembly
(Fig. 14). Compress barb on opposite side of retaining
pin, to prevent pin from breaking. CAUTION: Be extremely careful during the following
procedure to avoid damaging or puncturing brake
fluid reservoir during its removal.
(6) Remove brake fluid reservoir from hydraulic
assembly by carefullyprying between reservoir and
hydraulic assembly using a blunt pry bar (Fig. 15).
Use a rocking motion to help disengage reservoir
from grommets while prying. (7) Remove brake fluid level sensor from reservoir
and remove fluid reservoir from vehicle. (8) Remove hydraulic assembly wiring harness
connector from the primary pressure transducer (Fig.
16).
Fig. 11 Primary Pressure Transducer Location On Hydraulic Assembly
Fig. 12 Removing Bladder Accumulator
5 - 108 ANTI-LOCK 10 BRAKE SYSTEM Ä

(7) Using needle nose pliers, install the 3 brake fluid
reservoir to hydraulic assembly retaining pins (Fig.
14). Be sure retaining pins are fully installed with
barbs extending out past reservoir on opposite
side. (8) Install high pressure hose banjo fitting onto
hydraulic assembly and install banjo fitting attaching
bolt. Torque banjo fitting to hydraulic assembly banjo
bolt to 13 N Im (10 ft. lbs.).
(9) Install brake fluid spray shield onto hydraulic
assembly. Install bladder accumulator into hydraulic
assembly by hand (using care not to cross thread
accumulator) until O-ring seal is fully seated into
hydraulic assembly. (10) Using Oil Filter Band Wrench, Special Tool
C-4065 or equivalent, (Fig. 12) torque bladder accumu-
lator to 48 N Im (35 ft. lbs.).
(11) Fill hydraulic assembly fluid reservoir to the top
of the screen on the filter rainer. Use only fresh clean
brake fluid conforming to DOT 3 requirements, such as
Mopar tor equivalent.
(12) Bleed the brake hydraulic system using proce-
dure shown in Bleeding Brake System in this section of
the service manual.
DIFFERENTIAL PRESSURE SWITCH
REMOVE
WARNING: FAILURE TO FULLY DE-PRESSURIZE THE
HYDRAULIC BLADDER ACCUMULATOR PRIOR TO
REMOVING DIFFERENTIAL PRESSURE SWITCH.
WILL RESULT IN PERSONAL INJURY AND/OR DAM-
AGE TO PAINTED SURFACES OF THE VEHICLE.
To remove the differential pressure switch (Fig. 18),
from the hydraulic assembly, removal of the hydraulic
assembly from the vehicle is notrequired. (1) De-pressurize hydraulic bladder accumulator on
hydraulic assembly by pumping the brake pedal a
minimum of 40 times. Refer to the procedure as de-
scribed in De-Pressurizing Hydraulic Accumulator
listed earlier in this section. (2) Disconnect the hydraulic assembly wiring har-
ness connector from the primary pressure transducer
(Fig. 19).
(3) Disconnect differential pressure switch wiring
harness connector from hydraulic assembly wiring
harness (Fig. 19). Do not attempt to remove wiring
harness from differential pressure switch. (4) Raise vehicle on a frame contact type hoist. See
Hoisting in the Lubrication And Maintenance section
of this manual, for the required lifting procedure to be
used for this vehicle. (5) Using a long extension and Socket, Special Tool
6684 loosen and remove differential pressure switch
from bottom of hydraulic assembly (Fig. 20)
Fig. 18 Differential Pressure Switch Location
Fig. 19 Primary Pressure Transducer And Differen- tial Pressure Switch Wiring Harness Connectors
Fig. 17 Primary Pressure Transducer Removal And Replacement
5 - 110 ANTI-LOCK 10 BRAKE SYSTEM Ä

INSTALL (1) Install differential pressure switch into hydrau-
lic assembly by hand, until fully threaded into hy-
draulic assembly. Then torque differential pressure
switch, into hydraulic assembly, using Socket, Spe-
cial Tool 6684, to 1.5 N Im (13 in. lbs.).
(2) Lower vehicle
(3) Connect differential pressure switch wiring
harness connector into hydraulic assembly wiring
harness (Fig. 19). (4) Connect the hydraulic assembly wiring harness
connector into the primary pressure transducer (Fig.
19). (5) Turn the ignition switch to the on position and
let the system pressurize. Check for any signs of
leakage at the differential pressure switch. (6) Fully de-pressurize the hydraulic assembly a
second time to purge any air out that may have en-
tered hydraulic assembly when the differential pres-
sure switch was removed. Turn the ignition switch to
the on position and let the system pressurize again. (7) Fill hydraulic assembly fluid reservoir to the
top of the screen on the filter rainer. Use only fresh
clean brake fluid conforming to DOT 3 requirements,
such as Mopar tor equivalent.
(8) Road test vehicle to insure that the brake sys-
tem is performing correctly.
BOOST PRESSURE TRANSDUCER
REMOVE
WARNING: FAILURE TO FULLY DE-PRESSURIZE
THE HYDRAULIC BLADDER ACCUMULATOR PRIOR
TO REMOVING BOOST PRESSURE TRANSDUCER.
MAY RESULT IN PERSONAL INJURY AND/OR DAM-
AGE TO PAINTED SURFACES OF THE VEHICLE. To remove the boost pressure transducer (Fig. 21),
from the hydraulic assembly, removal of the hydrau-
lic assembly from the vehicle is notrequired.
(1) De-pressurize hydraulic bladder accumulator on
hydraulic assembly by pumping the brake pedal a
minimum of 40 times. Refer to the procedure as de-
scribed in De-Pressurizing Hydraulic Accumulator
listed earlier in this section. (2) Raise vehicle on a frame contact type hoist. See
Hoisting in the Lubrication And Maintenance section
of this manual, for the required lifting procedure to
be used for this vehicle. (3) Disconnect hydraulic assembly wiring harness
connectors from the dual function pressure switch
and boost pressure transducer (Fig. 21). (4) Using a long extension and Socket, Special Tool
6607, remove dual function pressure switch from bot-
tom of hydraulic assembly (Fig. 22)
(5) Remove boost pressure transducer from hydrau-
lic assembly, from under vehicle using a long exten-
sion and Socket, Special Tool 6684 (Fig. 23).
Fig. 20 Differential Pressure Switch Removal And Replacement
Fig. 21 Boost Pressure Transducer Location
Fig. 22 Remove And Install Dual Function Pressure Switch
Ä ANTI-LOCK 10 BRAKE SYSTEM 5 - 111

ANTI-LOCK BRAKE SYSTEMÐBENDIX ANTI-LOCK 6 AA,AG,AJ,AP BODY INDEX
page page
ABS Brake System Diagnosis .............. 123
ABS Brake System Diagnostic Features ...... 125
ABS Computer System Service Precautions . . . 124
ABS General Service Precautions ........... 124
Anti-Lock Brake System Components ........ 116
Anti-Lock Brake System Definitions .......... 113
Anti-Lock Brakes Operation and Performance . . 115
Anti-Lock System Relays and Warning Lamps . . 120
Controller Anti-Lock Brake (CAB) ............ 119
Diagnostic Connector ..................... 120
Electronic Components ................... 130 General Information
...................... 113
Hydraulic Circuits and Valve Operation ....... 121
Major Components ...................... 114
Mechanical Diagnostics and Service Procedures . 125
Normal Braking System Function ............ 114
On-Car ABS Brake System Service .......... 126
Specifications .......................... 135
System Self-Diagnostics .................. 115
Vehicle Performance ..................... 115
Warning Systems Operation ............... 116
GENERAL INFORMATION
The purpose of the Anti-Lock Brake System (ABS)
is to prevent wheel lock-up under heavy braking con-
ditions on virtually any type of road surface. Anti-
Lock Braking is desirable because a vehicle which is
stopped without locking the wheels will retain direc-
tional stability and some steering capability. This al-
lows the driver to retain greater control of the
vehicle during heavy braking. This section of the service manual covers the de-
scription, diagnostics, and on car service for the Ben-
dix Anti-Lock 6 Brake System. If other service is required on the non ABS related components of the
brake system. Refer to the appropriate section in this
group of the manual for the specific service procedure
required.
ANTI-LOCK BRAKE SYSTEM DEFINITIONS
In this section of the manual several abbreviations
are used for the components that are in the Anti-
Lock Braking System They are listed below for your
reference.
² CABÐController Anti-Lock Brake
² ABSÐAnti-Lock Brake System
Fig. 1 Four-Wheel Anti-Lock Brake System Components AA/AG/AJ Body
Ä ANTI-LOCK 6 BRAKE SYSTEM 5 - 113

If the vehicle is not set in motion within 3 minutes
from the time the ignition switch is set in the on po-
sition. The solenoid test is bypassed but the pump/
motor is activated briefly to verify that it is
operating correctly.
WARNING SYSTEMS OPERATION
The ABS system uses an Amber Anti-Lock Warn-
ing Lamp, located in the instrument cluster. The
purpose of the warning lamp is discussed in detail
below. The Amber Anti-Lock Warning Light will turn on
when the (CAB) detects a condition which results in
a shutdown of the Anti-Lock function. The Amber
Anti-Lock Warning Lamp is normally on until the
(CAB) completes its self tests and turns the lamp off
(approximately 1-2 seconds). When the Amber Anti-
Lock Warning Light is on only the Anti-Lock func-
tion of the brake system if affected. The standard
brake system and the ability to stop the car will not
be affected when only the Amber Anti-Lock Warning
Light is on.
NORMAL OPERATION OF WARNING LAMP
With the ignition in the Crank position, the Red
Brake Warning Lamp will turn on as a bulb check.
The Amber Anti-Lock Warning Lamp will stay on for
1-2 seconds then turn off. Once verification of the self
diagnosis is completed.
ANTI-LOCK BRAKE SYSTEM COMPONENTS
The following is a detailed description of the Anti-
Lock Brake System components. For information on
servicing the Four Wheel Disk Brake System, see the
standard Brake section of this Service Manual.
MODULATOR ASSEMBLY
WARNING: THE ONLY PART OF THE MODULATOR
ASSEMBLY THAT IS A SERVICEABLE COMPONENT
IS THE DELTA P SWITCH. THE REMAINING COM-
PONENTS OF THE MODULATOR ASSEMBLY ARE
NOT SERVICEABLE ITEMS. NO ATTEMPT SHOULD
BE MADE TO REMOVE OR SERVICE ANY OTHER
PARTS OF THE MODULATOR ASSEMBLY.
The Modulator Assembly (Fig. 1) is located under
the battery tray and is covered with an acid shield.
The Modulator Assembly contains the following com-
ponents for controlling the Anti-Lock braking sys-
tem. 2 Isolation Valves, 4 Build/Decay Valves, 4
Shuttle Orifices, 2 Fluid Sumps, 2 Accumulators, a
Pump/Motor and a Pressure Differential Valve/
Switch. Also attached to the Modulator Assembly are
4 brake tubes which are connected to an 8 way con-
nector block. The connector block is mounted to the
left frame rail below the master cylinder in the same location as the non ABS equipped combination valve.
The wheel brake lines are attached to the system via
the connector block.
ISOLATION VALVES
The Isolation Valves are used to isolate the master
cylinder from the rest of the brake hydraulic circuit
during an Anti-Lock stop. Two Isolation Valves are
used, one for the primary circuit and one for the sec-
ondary circuit. The Isolation Valves are spring
loaded in the released position. In the released posi-
tion the Isolation Valves provide a fluid path from
the master cylinder outputs to the wheel brakes via
the Build/Decay valves. When actuated it provides a
fluid path from the accumulator (which was charged
by the Pump/Motor during ABS operation) to the
Build/Decay valves through the Shuttle Orifices.
BUILD/DECAY VALVES
There are 4 Build/Decay valves, one for each
wheel. In the released position they provide a fluid
path from the wheel brakes to the Isolation Valve
through the shuttle orifices. In the actuated (decay)
position, they provide a fluid path from the wheel
brakes to the sump. The Build/Decay valves are
spring loaded in the released (build) position.
SHUTTLE ORIFICE
There are 4 Shuttle Orifice Valves, one for each
wheel. The Shuttle Orifice Valve is a hydraulically
actuated valve which shuttles when the Build/Decay
valve is actuated. Actuating of the Build/Decay valve
causes a pressure differential to be created across the
Shuttle Orifice Valve. This acts like placing an ori-
fice (restriction) in the line between the Isolation
Valve and the Build/Decay Valve. This restriction
provides a controlled build rate to each wheel brake
during an Anti-Lock stop. The Shuttle Orifice Valve
will remain in the orificed position until the ABS cy-
cle is complete. When the ABS cycle has been com-
pleted the Isolation and Build/Decay valves will
return to their released position which will equalize
the pressure across the Shuttle Orifice Valves. When
the pressure equalizes, the spring loaded Shuttle Or-
ifice valves will return to the unrestricted position.
FLUID SUMPS
There are two Fluid Sumps in the Hydraulic As-
sembly, one each for the primary and secondary hy-
draulic circuits. The Fluid Sumps store the brake
fluid that is decayed from the wheel brakes during
ABS cycle. This fluid is then pumped to an accumu-
lator and/or the hydraulic system in order to provide
build pressure. The typical pressure in the sumps is
50 psi, During ABS operation only.
5 - 116 ANTI-LOCK 6 BRAKE SYSTEM Ä

HYDRAULIC SPRING ACCUMULATOR
The Hydraulic Spring Accumulators (Fig. 2) (one
on each circuit) are used to store pressurized hydrau-
lic brake fluid during ABS operation only. This fluid
is used during hard braking when the ABS system is
activated, to supplement brake pressure when re-
quired. During normal Non ABS braking operation
there is NO pressurized brake fluid stored in the ac-
cumulators. The Hydraulic Spring Accumulators are
not a serviceable part of the Modulator Assembly
and should never be removed from the assembly.
PRESSURE DIFFERENTIAL VALVE/SWITCH
(DELTA P SWITCH)
The Pressure Differential Valve/Switch is located
inside the hydraulic assembly. This valve/switch func-
tions the same as the Pressure Differential
Valve/Switch located in the combination valve on stan-
dard brake systems. The delta P switch monitors the
primary and secondary hydraulic circuits for a differ-
ence in pressure. A pressure difference greater than
225 psi. Will move and latch the shuttle to ground the
Red Brake Warning Light circuit. This will in turn,
turn on the Red Brake Warning Light in the instru-
ment panel to warn the driver of a hydraulic system
problem. This Pressure Differential Valve Switch is a
replaceable item of the Modulator Assembly. The Red
Brake Warning Light indicates a problem with
the foundation brake system and not the Anti-
Lock system.
PUMP/MOTOR ASSEMBLY
The Modulator Assembly contains 2 Pump Assem-
blies, one each for the primary and secondary hydrau-
lic circuits. Both pumps are driven by a common
electric motor which is part of the Modulator Assembly.
The pumps pick up fluid from the sumps to supply
pressure to the accumulators or hydraulic system via
the isolation valves during an Anti-Lock stop. The
motor only runs during an ABS stop and is controlled
by the (CAB) via the Pump/Motor Relay. The
Pump/Motor Assembly is not a serviceable item. If it
requires service the Modulator Assembly must be re-
placed.
Fig. 1 Modulator Assembly
Fig. 2 Hydraulic Spring Accumulator
Ä ANTI-LOCK 6 BRAKE SYSTEM 5 - 117

CONTROLLER ANTI-LOCK BRAKE (CAB)
The Anti-Lock Brake Controller is a small micro-
processor based device which monitors the brake sys-
tem and controls the system while it functions in
Anti-Lock mode. The CAB is mounted on the top of
the right front frame rail and uses a 60-way system
connector (Fig. 7). The power source for the CAB is
through the ignition switch in the Run or On posi-
tion. THE CONTROLLER ANTI-LOCK BRAKE
(CAB) IS NOT ON THE CCD BUS The primary functions of the (CAB) are:
(1) Detect wheel locking tendencies.
(2) Control fluid modulation to the brakes while in
Anti-Lock mode. (3) Monitor the system for proper operation.
(4) Provide communication to the DRB II while in
diagnostic mode. The (CAB) continuously monitors the speed of each
wheel, through the signals generated at the Wheel
Speed Sensors, to determine if any wheel is begin-
ning to lock. When a front wheel locking tendency is
detected, the (CAB) will isolate the master cylinder
from the wheel brakes. This is done by activating the
Isolation Valves. The (CAB) then commands the ap-
propriate Build/Decay valves to modulate brake fluid
pressure in some or all of the hydraulic circuits. The
(CAB) continues to control pressure in individual hy-
draulic circuits until a locking tendency is no longer
present. The (ABS) system is constantly monitored by the
(CAB) for proper operation. If the (CAB) detects a
fault, it will turn on the Amber Anti-Lock Warning
Lamp and disable the ABS braking system. The nor-
mal Non ABS braking system will remain opera-
tional. The (CAB) contains a self-diagnostic program
which will turn on the Amber Anti-Lock Warning
Lamp when a system fault is detected. Faults are
stored in a diagnostic program memory. There are 16
fault codes which may be stored in the (CAB) and
displayed through the DRB II. These fault codes will
remain in the (CAB) memory even after the ignition
has been turned off. The fault codes can be cleared
by using the DRB II diagnostics tester, or they will
be automatically cleared from the memory after (50)
ignition switch on/off cycles.
CONTROLLER ANTI-LOCK BRAKE (INPUTS)
² Four wheel speed sensors.
² Stop lamp switch.
² Ignition switch.
² System relay voltage.
² Ground.
² Pump/Motor Relay Monitor
² Diagnostics Communications
CONTROLLER ANTI-LOCK BRAKE (OUTPUTS)
²6 modulator valves, 4 Build/Decay and 2 isolation
valves.
² Anti-Lock warning lamp.
² System relay actuation.
² Diagnostic communication.
² Pump motor relay actuation
Fig. 6 Tone Wheel (Typical)
Fig. 7 Location Controller Anti-Lock Brake (CAB)
Ä ANTI-LOCK 6 BRAKE SYSTEM 5 - 119

DIAGNOSTIC CONNECTOR
On the AA, AG, AJ and AP bodies, the Bendix An-
ti-Lock System diagnostic connector is located under
the fuse panel access cover. The access cover is lo-
cated on the lower section of the instrument panel on
the left side of the steering column. The diagnostics
connector is a blue 6 way connector see (Fig. 8).
ANTI-LOCK SYSTEM RELAYS AND WARNING
LAMPS
SYSTEM RELAY
The (ABS) Modulator Valves and Anti-Lock Warn-
ing Lamp Relay. Are powered through a System Re-
lay located on a bracket mounted to the (CAB) see
(Fig. 9) for location of the relay. The System Relay
provides power to the (CAB) for modulator valve op-
eration (pins 47 and 41) after the startup cycle when
the ignition is turned on.
ANTI-LOCK WARNING LAMP RELAY
The Amber Anti-Lock Warning Lamp is controlled
by the Anti-Lock Warning Lamp relay. The relay is
mounted to the same bracket as the system relay at
the (CAB) see (Fig. 9). With the relay de-energized,
the lamp is lit. When the System Relay is energized
by the (CAB), the Anti-Lock warning lamp relay is
energized, and the lamp is turned off. Thus, the lamp
will be lit if the (CAB) is disconnected or if a system
fault causes the (ABS) function to be turned off.
PUMP/MOTOR RELAY
Pump/Motor power is supplied by the Pump/Motor
Relay. The Pump/Motor Relay is either mounted on
the left front inner fender shield, or the front of the
left shock tower. The mounting location is dependent
on whether the vehicle is or is not equipped with a
power distribution center. See (Fig. 10 and 11) for
specific mounting locations.
ANTI-LOCK WARNING LAMP OFF
System Relay and Anti-Lock Warning Lamp
Relay Energized From pin 57 the (CAB) energizes the system relay
coil. The electrical current flow in the coil closes the
system relay. Then electrical current is provided to
pins 47 and 41 of the (CAB) to provide power to the
modulator valves. This electrical current also ener-
gizes the Amber Anti-Lock Warning Lamp Relay
coil. The current flow in the Anti-Lock Warning
Fig. 8 A.B.S. Diagnostic Connector Location
Fig. 9 System Relay/Warning Lamp Relay
Fig. 10 Pump Motor Relay With Power Distribution Center
5 - 120 ANTI-LOCK 6 BRAKE SYSTEM Ä

Lamp Relay opens the Anti-Lock Warning Lamp Re-
lay switch. This breaks the ground path to the Am-
ber Anti-Lock Warning Lamp and the light is turned
off. The (CAB) by itself, also has the ability to turn on
the Amber Anti-Lock Warning Lamp. The (CAB) can
turn on the Amber Anti-Lock Warning Lamp by pro-
viding a ground at pin 15.
ANTI-LOCK WARNING LAMP ON
System Relay and Anti-Lock Warning Lamp
Relay De-Energized. When the Amber Anti-Lock Warning Lamp is on,
there is no electrical current flow from the (CAB) at
pin 57. The System Relay coil is NOT energized. No
electrical current flows to pin 47 and 41 (modulator
valve power), or to the Anti-Lock Warning Lamp Re-
lay coil. Thus, the Amber Anti-Lock Warning Lamp
is not energized. The Amber Anti-Lock Warning Lamp is grounded through the Anti-Lock Warning
Lamp Relay contacts. The Amber Anti-Lock Warning
Lamp is turned on.
HYDRAULIC CIRCUITS AND VALVE OPERATION
Through the following operation descriptions and
diagrams. The function of the various hydraulic con-
trol valves in the ABS system will be described. The
fluid control valves mentioned below, control the flow
of pressurized brake fluid to the wheel brakes during
the different modes of Anti-Lock braking. For explanation purposes we will assume all speed
sensors are sending the same wheel speed informa-
tion, requiring the same hydraulic fluid modulation
at the same rate.
NORMAL BRAKING
ISOLATION VALVES
Open to primary and secondary master cylinder
fluid supply (Fig. 1)
BUILD/DECAY VALVES Closed (Fig. 1)
The brake pedal is applied. The travel of the brake
pedal closes primary and secondary circuits from the
master cylinder fluid supply. Brake fluid from the
primary and secondary circuits flows through the
open isolation valves, through the build/decay valves
to the wheel brakes.
ABS BRAKING-BUILD PRESSURE
ISOLATION VALVES
Closed, isolating wheel brakes from master cylin-
der primary and secondary fluid supply. Through
open build valves (Fig. 2).
BUILD/DECAY VALVES Open (Fig. 2)
Fig. 11 Pump Motor Relay W/O Power Distribution Center
Ä ANTI-LOCK 6 BRAKE SYSTEM 5 - 121