abs CHEVROLET DYNASTY 1993 Manual PDF

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

ABS BRAKING-DECAY PRESSURE
ISOLATION VALVES Closed, isolating the wheel brakes from the master
cylinder primary and secondary fluid supplies (Fig.
3)
BUILD/DECAY VALVES
Open, allowing release of fluid pressure through
decay valve to the fluid reservoir. Which gets
pumped into the accumulator for the build pressure
cycle (Fig. 3).
ABS BRAKE SYSTEM DIAGNOSIS
GENERAL INFORMATION
WARNING: SOME OPERATIONS IN THIS SECTION
REQUIRE THAT HYDRAULIC TUBES, HOSES AND
FITTINGS BE DISCONNECTED FOR INSPECTION
OR TESTING PURPOSES.
CAUTION: REVIEW THIS ENTIRE SECTION PRIOR
TO PERFORMING ANY MECHANICAL WORK ON A
VEHICLE EQUIPPED WITH THE BENDIX ANTI-LOCK
6 BRAKE SYSTEM. THIS SECTION CONTAINS IN-
FORMATION ON PRECAUTIONS PERTAINING TO
POTENTIAL COMPONENT DAMAGE, VEHICLE DAM- AGE AND PERSONAL INJURY WHICH COULD RE-
SULT WHEN SERVICING AN ABS EQUIPPED
VEHICLE.
CAUTION: Certain components of the Anti-Lock
Brake System (ABS) are not intended to be serviced
individually. Attempting to remove or disconnect
certain system components, may result in personal
injury and/or improper system operation. Only
those components with approved removal and in-
stallation procedures in this manual should be ser-
viced.
This section contains information necessary to di-
agnosis mechanical conditions which can affect oper-
ation of the Bendix Anti-Lock 6 Brake System.
Specifically, this section should be used to help diag-
nose mechanical conditions which result in any of
the following: (1) Anti-Lock Warning Lamp turned on.
(2) Brakes Lock on Hard Application
Diagnosis of conditions which are obviously me-
chanical in nature. Such as brake noise, brake pulsa-
tion, lack of power assist, turning on of the Red
Brake Warning Lamp or vehicle vibration during
normal braking. Should be directed to Group 5
Brakes in this service manual. This also pertains to
problems involving the parking brake system.
Fig. 3 Decay Pressure - Hydraulic Control
Ä ANTI-LOCK 6 BRAKE SYSTEM 5 - 123

In order to effectively diagnose an Anti-Lock Brake
System (ABS) condition. It is important to read Anti-
Lock Brake System Description. And to follow the
diagnostic procedures outlined in this section. Many conditions that generate customer complaints
may be normal operating conditions, but are judged to
be a problem due to not being familiar with the ABS
system. These conditions can be recognized without
performing extensive diagnostic work. Given adequate
understanding of the operating principles and perfor-
mance characteristics of the ABS system. See Section 1
of this manual to familiarize yourself with the operat-
ing principles of the ABS system.
DEFINITIONS
Several abbreviations are used in this manual. They
are presented here for reference.
² CABÐController Anti-Lock Brake
² ABSÐAnti-Lock Brake System
² PSIÐPounds per Square Inch (pressure)
² WSSÐWheel Speed Sensor
ABS COMPUTER SYSTEM SERVICE PRECAUTIONS
The ABS system uses an electronic control module,
the (CAB). This module is designed to withstand nor-
mal current draws associated with vehicle operation.
However care must be taken to avoid overloading the
(CAB) circuits. In testing for open or short circuits,
do not ground or apply voltage to any of the
circuits unless instructed to do so by the appro-
priate diagnostic procedure. These circuits should
only be tested using a high impedance multi-meter,
special tools or the DRB II tester as described in this
section. Power should never be removed or applied to
any control module with the ignition in the ON posi-
tion. Before removing or connecting battery cables,
fuses, or connectors, always turn the ignition to the
OFF position.
ABS GENERAL SERVICE PRECAUTIONS
TEST DRIVING ABS COMPLAINT VEHICLES
Most ABS complaints will require a test drive as a
part of the diagnostic procedure. The purpose of the
test drive is to duplicate the condition. Remember conditions that result in the turn-
ing on of the Red Brake Warning Lamp may
indicate reduced braking ability. The following
procedure should be used to test drive an ABS
complaint vehicle. Before test driving a brake complaint vehicle, note
whether the Red or Amber Brake Warning Lamp is
turned on. If it is the Red Brake Warning Lamp, refer
to the standard brake, Control Valves Section in the
brake group of this manual. If the Amber Anti-Lock
Warning light was/is on, read record and erase the
fault. While the Amber ABS Warning Lamp is on the
ABS system is not functional. When the Am- ber Anti-Lock Warning Lamp is on only the Anti-Lock
function of the brake system if affected. The standard
brake system and the ability to stop the car is not be
affected if only the Amber Anti-Lock Warning Lamp is
on. (1) Turn the key to the off position and then back to
the on position. Note whether the Amber ABS Warning
Lamp continues to stay on. If it does refer to the 1993
M.Y. Bendix Anti-Lock 6 Diagnostic Manual for the
required test procedures. (2) If the Amber ABS Warning Lamp goes out, shift
into gear and drive the car to a speed of 5 mph to
complete the ABS start up cycle. If at this time the
Amber ABS Warning Lamp goes on refer to the Bendix
Anti-Lock 6 Diagnostic Manual. (3) If the Amber ABS Warning Lamp remains OUT,
drive the vehicle a short distance. During this test
drive be sure that the vehicle achieves at least 25 mph.
Brake to at least one complete stop and again acceler-
ate to 25 mph. (4) If a functional problem with the A.B.S. system is
determined while test driving a vehicle. Refer to the
Bendix Anti-Lock 6 Diagnostics Manual for required
test procedures and proper use of the DRB II tester.
ABS BRAKE SYSTEM ON VEHICLE SERVICE
The following are general precautions which
should be observed when servicing and diagnos-
ing the ABS system and/or other vehicle systems.
Failure to observe these precautions may result
in ABS system damage. (1) If welding work is to be performed on a vehicle
using an arc welder, the (CAB) should be disconnected
before the welding operation begins. (2) The (CAB) and modulator assembly 10 way con-
nector should never be connected or disconnected with
the ignition in the on position. (3) Some components of the ABS system are not
serviced separately and must be serviced as complete
assemblies. Do not disassemble any component which
is designated as non-serviceable.
CAUTION: Brake fluid will damage painted surfaces.
If brake fluid is spilled on any painted surfaces, wash
off with water immediately.
WHEEL SPEED SENSOR CABLES
Proper installation of the Wheel Speed Sensor Cables
is critical to continued system operation. Be sure that
cables are installed, routed and clipped properly. Fail-
ure to install speed sensor cables as shown in the on
car service section of this manual. May result in
contact with moving parts or over extension of cables,
resulting in component failure and an open circuit.
5 - 124 ANTI-LOCK 6 BRAKE SYSTEM Ä

MECHANICAL DIAGNOSTICS AND SERVICE
PROCEDURES
SPECIAL SERVICE TOOL
Some diagnostic procedures in this section require
the use of the DRB II diagnostics tester. The proper
application and procedures for the use of this tool are
described below.
DRB II DIAGNOSTIC TESTER Some of the diagnostic procedures that are ex-
plained in this section require the use of the DRB II
Diagnostics Tester to insure that proper diagnostics
are performed. Refer to those sections for proper test-
ing procedures and the DRB II operators manual for
its proper operational information.
INTERMITTENT FAULTS
As with virtually any electronic system, intermit-
tent faults in the ABS system may be difficult to ac-
curately diagnose. Most intermittent faults are caused by faulty elec-
trical connections or wiring. When an intermittent
fault is encountered, check suspect circuits for: (1) Poor mating of connector halves or terminals
not fully seated in the connector body. (2) Improperly formed or damaged terminals. All
connector terminals in a suspect circuit should be
carefully reformed to increase contact tension. (3) Poor terminal to wire connection. This requires
removing the terminal from the connector body to in-
spect. (4) Pin presence in the connector assembly
If a visual check does not find the cause of the
problem, operate the car in an attempt to duplicate
the condition and record the Fault code. Most failures of the ABS system will disable Anti-
Lock function for the entire ignition cycle even if the
fault clears before key-off. There are some failure
conditions, however, which will allow ABS operation
to resume during the ignition cycle in which a fail-
ure occurred. If the failure conditions are no longer
present. The following conditions may result in inter-
mittent illumination of the Amber Anti-Lock Warn-
ing Lamp. All other failures will cause the lamp to
remain on until the ignition switch is turned off. Cir-
cuits involving these inputs to the (CAB) should be
investigated if a complaint of intermittent warning
system operation is encountered. (1) Low system voltage. If Low System Voltage is
detected by the (CAB), the (CAB) will turn on the
Amber Anti-Lock Warning Lamp until normal sys-
tem voltage is achieved. Once normal voltage is seen
at the (CAB), normal operation resumes. (2) Anti-Lock relay. If the relay fails to make the
ground circuit connection or is an intermittent
ground. The (CAB) will turn on the Amber Anti-Lock
Warning Light. (3) Excess decay, an extended pressure decay pe-
riod, will turn on the Amber Anti-Lock Warning
Light until the vehicle comes to a complete stop. Additionally, any condition which results in inter-
ruption of electrical current to the (CAB) or modula-
tor assembly. May cause the Amber Anti-Lock
Warning Lamp to turn on intermittently.
ABS BRAKE SYSTEM DIAGNOSTIC FEATURES
ABS SYSTEM SELF DIAGNOSIS
The ABS system is equipped with a self diagnostic
capability which may be used to assist in isolation of
ABS faults. The features of the self diagnostics sys-
tem are described below.
START-UP CYCLE
The self diagnostic ABS start up cycle begins when
the ignition switch is turned to the on position. An
electrical check is completed on the ABS components.
Such as Wheel Speed Sensor Continuity and System
and other Relay continuity. During this check the
Amber Anti-Lock Light is turned on for approxi-
mately 1- 2 seconds. Further Functional testing is accomplished once
the vehicle is set in motion.
² The solenoid valves and the pump/motor are acti-
vated briefly to verify function.
² The voltage output from the wheel speed sensors is
verified to be within the correct operating range. 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.
CONTROLLER ANTI-LOCK BRAKE (CAB)
Fault codes are kept in a Non-Volatile memory un-
til either erased by the technician using the DRB II
or erased automatically after 50 ignition cycles (key
ON-OFF cycles). The only fault that will not be
erased after 50 (KEY CYCLES) is the (CAB) fault. A
(CAB) fault can only be erased by the technician us-
ing the DRB II diagnostic tester. More than one fault
can be stored at a time. The number of key cycles
since the most recent fault was stored is also dis-
played. Most functions of the (CAB) and ABS system
can be accessed by the technician for testing and di-
agnostic purposes by using the DRB II.
LATCHING VERSUS NON-LATCHING ABS FAULTS
Some faults detected by the (CAB) are latching; the
fault is latched and (ABS) is disabled until the igni-
tion switch is reset. Thus ABS is disabled even if the
original fault has disappeared. Other faults are non-
latching; any warning lights that are turned on, are
only turned on as long as the fault condition exists.
Ä ANTI-LOCK 6 BRAKE SYSTEM 5 - 125

As soon as the condition goes away, the Anti-Lock
Warning Light is turned off. Although a fault code
will be set in most cases.
BENDIX ABS SYSTEMS DIAGNOSTICS
Bendix Anti-Lock 6 Brake System Diagnostics, be-
yond basic mechanical diagnostics, covered earlier in
this section. Are accomplished by using the DRB II
scan tool. See testing procedures outlined in the Ben-
dix Anti-Lock 6 Diagnostics Manual for the 1992
M.Y. vehicles. Please refer to the above mentioned manual for
any further electronic diagnostics and service proce-
dures that are required on the Bendix Anti-Lock 6
Brake System.
ON-CAR ABS BRAKE SYSTEM SERVICE
GENERAL SERVICE PRECAUTIONS
The following are general cautions which should be
observed when servicing the Anti-Lock brake system
and/or other vehicle systems. Failure to observe
these precautions may result in Anti-Lock Brake
System component damage. If welding work is to be performed on the vehicle,
using an electric arc welder, the (CAB) connector
should be disconnected during the welding operation. The (CAB) connector should never be connected or
disconnected with the ignition switch in the ON po-
sition. Many components of the Anti-Lock Brake System
are not serviceable and must be replaced as an as-
sembly. Do not disassemble any component which is
not designed to be serviced.
CHECKING BRAKE FLUID LEVEL
CAUTION: Only use brake fluid conforming to DOT
3 specifications, such as Mopar or Equivalent. Do
not use any fluid which contains a petroleum base.
Do not use a container which has been used for pe-
troleum based fluids or a container which is wet
with water. Petroleum based fluids will cause swell-
ing and distortion of rubber parts in the hydraulic
brake system. Water will mix with brake fluid, low-
ering the fluid boiling point. Keep all brake fluid
containers capped to prevent contamination. Re-
move the front cap of the master cylinder reservoir
and fill to the bottom of the split ring.
For the specific procedure for the inspection of
brake fluid level and adding of brake to the reser-
voir. Refer to the Service Adjustments Section in this
group of the service manual.
BLEEDING BENDIX ANTI-LOCK 6 BRAKE SYSTEM
The Anti-Lock Brake System must be bled anytime
air is permitted to enter the hydraulic system, due to
disconnection of brake lines, hoses of components. If the Modulator Assembly is removed from the ve-
hicle, both the Base Brake System and the Anti-Lock
Brake System must be bled using the appropriate
procedures. It is important to note that excessive air
in the brake system will cause a soft or spongy feel-
ing brake pedal. During bleeding operations, be sure that the brake
fluid level remains close to the FULL level in the
reservoir. Check the fluid level periodically during
the bleeding procedure and add DOT 3 brake fluid as
required. The Bendix Anti-Lock 6 Brake System must be
bled as two independent braking systems. The non
ABS portion of the brake system is to be bled the
same as any non ABS system. Refer to the Service
Adjustments section in this manual for the proper
bleeding procedure to be used. This brake system can
be either pressure bled or manually bled. The Anti-Lock portion of brake system MUST be
bled separately. This bleeding procedure requires the
use of the DRB II Diagnostic tester and the bleeding
sequence procedure outlined below.
ABS BLEEDING PROCEDURE (FIG. 1)
(1) Assemble and install all brake system compo-
nents on vehicle making sure all hydraulic fluid
lines are installed and properly torqued. (2) Bleed the base brake system. Using the stan-
dard pressure or manual bleeding procedure as out-
lined in the Service Adjustments section of this
service manual. To perform the bleeding procedure on the ABS
unit. The battery and acid shield must be removed
from the vehicle. Reconnect the vehicles battery, to
the vehicles positive and negative battery cables us-
ing jumper cables. This is necessary to allow access
to the 4 bleeder screws located on the top of the Mod-
ulator assembly. (3) Connect the DRB II Diagnostics Tester to the
diagnostics connector. Located behind the Fuse Panel
access cover on the lower section of the dash panel to
the left of the steering column. (It is a blue 6 way
connector). (4) Using the DRB II check to make sure the
(CAB) does not have any fault codes stored. If it does
remove them using the DRB II.
5 - 126 ANTI-LOCK 6 BRAKE SYSTEM Ä

WARNING: WHEN BLEEDING THE MODULATOR
ASSEMBLY WEAR SAFETY GLASSES. A CLEAR
BLEED TUBE MUST BE ATTACHED TO THE
BLEEDER SCREWS AND SUBMERGED IN A CLEAR
CONTAINER FILLED PART WAY WITH CLEAN
BRAKE FLUID. DIRECT THE FLOW OF BRAKE
FLUID AWAY FROM THE PAINTED SURFACES OF
THE VEHICLE. BRAKE FLUID AT HIGH PRESSURE
MAY COME OUT OF THE BLEEDER SCREWS,
WHEN OPENED.
When bleeding the Modulator Assembly. The fol-
lowing bleeding sequence MUSTbe followed to in-
sure complete and adequate bleeding of the brakes
hydraulic system. The Modulator Assembly can be
bled using a Manual bleeding procedure or standard
Pressure Bleeding Equipment. If the brake system is to be bled using pressure
bleeding equipment. Refer to Bleeding Brake System,
in the Service Adjustments section at the beginning
of this group, for proper equipment usage and proce-
dures.
MODULATOR ASSEMBLY BLEEDING SEQUENCE
1 SECONDARY SUMP
(1) Put a bleeder tube on the Secondary Sump
bleeder screw (Fig. 1). (2) Use a pressure bleeder, or have an assistant,
apply light and constant pressure on the brake pedal.
Loosen the Secondary Sump bleeder screw (Fig. 1). (3) Using the DRB II select the Actuate Valves
test mode. Then actuate the LF Build/Decay Valve. (4) Bleed the Secondary Sump. Until a clear air
free flow of brake fluid is evident in the clear hose
and no air bubbles appear in the container, or the
brake pedal bottoms. (5) Tighten the bleeder screw and release the
brake pedal. (6) Repeat steps 2 through 5 until a clear air free
flow of brake fluid is coming out of the Secondary
Sump bleeder screw. (7) Next select and actuate the RR Build/Decay
Valve. Again repeat steps 2 through 5 until a clean
air free flow of brake fluid is coming out of the Sec-
ondary Sump bleeder screw.
2 PRIMARY SUMP
(1) Put a bleeder tube on the Primary Sump
bleeder screw (Fig. 1). (2) Use a pressure bleeder, or have an assistant,
apply light and constant pressure on the brake pedal.
Loosen the Primary Sump bleeder screw (Fig. 1). (3) Using the DRB II select the Actuate Valves
test mode. Then actuate the RF Build/Decay Valve. (4) Bleed the Primary Sump. Until a clear air free
flow of brake fluid is evident in the clear hose and no
air bubbles appear in the container, or the brake
pedal bottoms. (5) Tighten the bleeder screw and release the
brake pedal. (6) Repeat steps 2 through 5 until a clear air free
flow of brake fluid is coming out of the Primary
Sump bleeder screw. (7) Next select and actuate the LR Build/Decay
Valve. Again repeat steps 2 through 5 until a clean
air free flow of brake fluid is coming out of the Pri-
mary Sump bleeder screw.
3 PRIMARY ACCUMULATOR
(1) Put a bleeder tube on the Primary Accumulator
bleeder screw. (Fig. 1) (2) Use a pressure bleeder, or have an assistant,
apply light and constant pressure on the brake pedal.
Loosen the Primary Accumulator bleeder screw (Fig.
1). (3) Using the DRB II select the Actuate Valves
test mode. Then actuate the RF/LR Isolation Valve. (4) Bleed the Primary Accumulator. Until a clear
air free flow of brake fluid is evident in the clear
hose and no air bubbles appear in the container, or
the brake pedal bottoms. (5) Tighten the bleeder screw and release the
brake pedal.
Fig. 1 Bleeding ABS Modulator Assembly
Ä ANTI-LOCK 6 BRAKE SYSTEM 5 - 127