1993 CHEVROLET PLYMOUTH ACCLAIM relay

ANTILOCK BRAKES OPERATION AND
PERFORMANCE
The Bendix Antilock 4 Brake System represents
the current state-of-the-art in vehicle brake systems
and offers the driver increased safety and control
during braking. This is accomplished by a sophisti-
cated system of electrical and hydraulic components.
As a result, there are a few performance characteris-
tics that may at first seem different but should be
considered normal. These characteristics are dis-
cussed below. More technical details are discussed
further in this section.
PEDAL FEEL
Since the Bendix Antilock 4 Brake System uses the
vehicle's conventional brake system power booster
and master cylinder. The brake pedal feel during
normal braking is the same as on a conventional
Non ABS equipped vehicle. When the Antilock system becomes activated dur-
ing hard braking due to a wheel lockup tendency.
The brake pedal effort will increase do to the master
cylinder pressure being isolated from the brake sys-
tem. Some brake pedal movement and associated
noises may be felt and heard by the driver. This is
normal operation of the Bendix Antilock 4 Brake
System due to pressurized brake fluid being trans-
ferred to and from the wheel brakes.
ANTILOCK BRAKE SYSTEM OPERATION
During Antilock Brake system operation, brake
pressures are modulated by cycling electric solenoid
valves. The cycling of these valves can be heard as a
series of popping or ticking noises. In addition, the
cycling may be felt as a pulsation in the brake pedal.
If Antilock operation occurs during a hard applica-
tion of the brakes, some pulsation may be felt in the
vehicle body due to fore and aft movement of vehicle
suspension components. Although ABS operation is available at virtually
all vehicle speeds, it will automatically turn off at
speeds below 3 to 5 mph. Wheel lockup may be per-
ceived at the very end of an anti lock stop and is con-
sidered normal.
TIRE NOISE & MARKS
Although the ABS system prevents complete wheel
lock-up, some wheel slip is desired in order to
achieve optimum vehicle braking performance. During brake fluid pressure modulation, as the
brake fluid pressure is increased, wheel slip is al-
lowed to reach up to 30%. This means that wheel
rolling speed is 30% less than that of a free rolling
wheel at a given vehicle speed. This slip may result
in some tire chirping, depending on the road surface.
This sound should not be interpreted as total wheel
lock-up. Complete wheel lock up normally leaves black tire
marks on dry pavement. The Antilock Brake System
will not leave dark black tire marks since the wheel
never reaches a locked condition. Tire marks may
however be noticeable as light patched marks.
VEHICLE PERFORMANCE
Antilock Brakes provide the driver with some
steering control during hard braking, however there
are conditions where the system does not provide any
benefit. In particular, hydroplaning is still possible
when the tires ride on a film of water. This results in
the vehicles tires leaving the road surface rendering
the vehicle virtually uncontrollable. In addition, ex-
treme steering maneuvers at high speed or high
speed cornering beyond the limits of tire adhesion to
the road surface may cause vehicle skidding, inde-
pendent of vehicle braking. For this reason, the ABS
system is termed Antilock instead of Anti-Skid.
SYSTEM SELF-DIAGNOSTICS
The Bendix Antilock 4 Brake System has been de-
signed with the following self diagnostic capabilities. The self diagnostic ABS startup cycle begins when
the ignition switch is turned to the on position. At
this time 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 Antilock Light is on for approxi-
mately 1-2 seconds. Further Antilock Brake System functional testing
is accomplished once the vehicle is set in motion,
known as drive-off. (1) The solenoid valves and the pump/motor are ac-
tivated briefly to verify function.
Fig. 5 Controller Antilock Brake CAB
Ä ANTILOCK 4 BRAKE SYSTEM 5 - 15

fice (restriction) in the line between the wheel and
the Build/Decay Valve. This restriction provides a
controlled build rate to each wheel brake during an
Antilock stop. The Shuttle Orifice Valve will remain
in the orificed position until the ABS cycle is com-
plete. When the ABS cycle has been completed the
Build/Decay valves will return to their released posi-
tion which will equalize the pressure across the
Shuttle Orifice Valves. When the pressure equalizes,
the spring loaded Shuttle Orifice valves will return
to the unrestricted position.
FLUID SUMPS
There are two Fluid Sumps in the Hydraulic As-
sembly, one for the primary and secondary hydraulic
circuits. The Fluid Sumps store the brake fluid that
is decayed from the wheel brakes during an ABS cy-
cle. This fluid is then pumped to an accumulator
and/or the hydraulic system in order to provide build
pressure. The typical pressure in the sumps is 50 psi,
during ABS operation only.
HYDRAULIC SPRING ACCUMULATOR
The Hydraulic Spring Accumulators (Fig. 3) (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 brake 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 SWITCH
The Pressure Differential Switch on the Bendix An-
tilock 4 Brake System is located on the frame rail
mounted brake hydraulic tube junction block. This
switch functions the same as the Pressure Differential
Switch located in the combination valve on standard
non ABS brake system. The pressure differential
switch monitors the primary and secondary hydraulic
brake circuits for a difference in pressure. A pressure
difference greater than 225 psi., will move and latch
the switch, grounding the Red Brake Warning Light
circuit. This will in turn, turn on the Red Brake
Warning Light in the instrument panel to warn the
driver of a pressure loss in one of the brake hydraulic
systems. This pressure differential switch is a replace-
able item of the junction block assembly. The Red
Brake Warning Light only indicates a problem
with the foundation brake hydraulic system and
not the Antilock 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 take brake fluid from the sumps to supply
pressure to the accumulators or hydraulic system via
the shuttle orifice during an Antilock 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 replaced.
PROPORTIONING VALVES
Two Proportioning Valves (Fig. 4) are used in the
Bendix Antilock 4 Brake System, one for each of the
rear wheel brake hydraulic circuits. The Proportioning
Valves function the same as in a standard brake
system. The Proportioning Valves are located on the
side of the modulator assembly (Fig. 1). Each rear
wheel hydraulic brake line, is connected to an indi-
vidual proportioning valve.
Fig. 3 Hydraulic Spring Accumulator
Fig. 4 Proportioning Valve Identification
Ä ANTILOCK 4 BRAKE SYSTEM 5 - 17

(4) Provide communication to the DRB II while in
the Antilock brakes diagnostic mode. The CAB continuously monitors the speed of each
wheel, through the signals generated at the Wheel
Speed Sensors. This is used to determine if any
wheel of the vehicle is beginning to lock-up (skid)
when the brakes are applied. When a wheel locking
tendency is detected during brake apply. The CAB
commands the appropriate Build/Decay valves to
modulate brake fluid pressure in some or all of the
hydraulic circuits. The CAB continues to control
pressure in individual hydraulic circuits until a lock-
ing 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 Antilock Warning Lamp
and disable the ABS brake system. The normal Non
ABS brake system will remain operational. The CAB contains a self-diagnostic program which
will turn on the Amber Antilock 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 auto-
matically cleared from the memory after (50) ignition
switch on/off cycles.
CONTROLLER ANTILOCK 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 ANTILOCK BRAKE (OUTPUTS)
²4 Build/Decay valves.
² Antilock warning lamp.
² System relay actuation.
² Diagnostic communication.
² Pump/Motor relay actuation
DIAGNOSTIC CONNECTOR
The Bendix Antilock 4 Brake System diagnostic
connector is located under the fuse panel access
cover. The access cover is located on the lower sec-
tion of the instrument panel to the left side of the
steering column. The diagnostics connector is a blue
6 way connector see (Fig. 9).
ANTILOCK SYSTEM RELAYS AND WARNING LAMPS
SYSTEM RELAY
The ABS Modulator Valves are powered through
the System Relay which is located on a bracket
mounted to the CAB (Fig. 10). The System Relay
provides power to the CAB for modulator valve oper-
ation (pins 47 and 41) after the startup cycle when
the ignition is turned on.
Fig. 8 CAB Location
Fig. 9 Antilock Diagnostic Connector Location
Fig. 10 System Relay Location On The CAB
Ä ANTILOCK 4 BRAKE SYSTEM 5 - 19

ANTILOCK WARNING LAMP DIODE
The Warning Lamp Relay on the Bendix Antilock
4 Brake System has been replaced with a diode. The
diode is used to control the function of the warning
lamp and is located inside the CAB module wiring
harness. The diode is a replaceable component of the
wiring harness, and will not require replacement of
the entire wiring harness if only the diode is diag-
nosed to have failed. When the system relay is de-energized, the Anti-
lock warning lamp will be lit. This will occur because
a ground path exists for the Antilock warning lamp
through the Antilock warning lamp diode and the
system relay armature. When the system relay is en-
ergized by the CAB, the system relay armature will
no longer provide a ground and the lamp will turn
off. Thus, the lamp will be lit if either the CAB is
disconnected or a system fault causes the Antilock 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. 11 and 12) for
specific mounting locations.
ANTILOCK WARNING LAMP OFF
System Relay Energized
From pin 57, the CAB energizes the Antilock sys-
tem relay coil, thus 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. The CAB turns off the Amber Antilock Warning
Lamp by breaking the ground path through pin 15 of
the CAB.
ANTILOCK WARNING LAMP ON
System Relay De-Energized.
When the Amber Antilock Warning Lamp is on,
there is no electrical current flow from the CAB at
pin 57 and the System Relay coil is NOT energized.
No electrical current flows to pin 47 and 41 (modula-
tor valve power), or to the Antilock Warning Lamp
diode. Thus, the Amber Antilock Warning Lamp is
not energized. The Amber Antilock Warning Lamp is
now grounded through the Antilock Warning Lamp
diode and pin 15 of the CAB turning on the Amber
Antilock Warning Lamp.
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 Antilock 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
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
master cylinder primary and secondary circuits flows
through the build/decay valves to the wheel brakes.
ABS BRAKING-BUILD PRESSURE
BUILD/DECAY VALVES
Open (Fig. 2)
Fig. 11 Pump Motor Relay Location On AA Body W/O Power Distribution Center
Fig. 12 Pump Motor Relay Location On AJ BodyWith Power Distribution Center
5 - 20 ANTILOCK 4 BRAKE SYSTEM Ä

manual. May result in contact with moving parts or
over extension of cables, resulting in component fail-
ure and an open circuit.
MECHANICAL DIAGNOSTICS AND SERVICE
PROCEDURES
SPECIAL SERVICE TOOL
Some diagnostic procedures in this section require
the use of the DRB diagnostics tester. The proper ap-
plication and procedures for the use of this tool are
described below.
DRB DIAGNOSTIC TESTER
Some of the diagnostic procedures that are ex-
plained in this section require the use of the DRB Di-
agnostics Tester to insure that proper diagnostics are
performed. Refer to those sections for proper testing
procedures and the DRB 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 wiring harness 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
checked and carefully reformed to increase contact
tension with its mating terminal. (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
(5) Connector push-in, spread, and corrosion.
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 set Fault code. Most failures of the ABS system will disable the
Antilock 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 it oc-
curred, if the failure condition is no longer present.
The following conditions may result in intermittent
illumination of the Amber Antilock Warning Lamp.
All other failures will cause the lamp to remain on
until the ignition switch is turned off. Circuits in-
volving these inputs to the CAB should be investi-
gated 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 Am-
ber Antilock Warning Lamp until normal system voltage is achieved. Once normal voltage is seen at
the CAB, normal operation resumes.
(2) Antilock system and pump/motor relay. If the
relays fail to make the ground circuit connection or
has an intermittent ground. The CAB will turn on
the Amber Antilock Warning Light. (3) Excess decay, an extended pressure decay pe-
riod, will turn on the Amber Antilock 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 modulator
assembly, may cause the Amber Antilock 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 Antilock Light is turned on for approximately
1- 2 seconds. Further Functional testing is accomplished once
the vehicle is set in motion, known as drive-off.
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 ANTILOCK BRAKE CAB
Fault codes are kept in a Non-Volatile memory un-
til either erased by the technician using the DRB 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 using
the DRB 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 displayed.
Most functions of the CAB and ABS system can be
accessed by the technician for testing and diagnostic
purposes by using the DRB.
5 - 24 ANTILOCK 4 BRAKE SYSTEM Ä

(10) Install battery on battery tray and install and
securely tighten the battery hold down clamp (Fig.
13). Then install heat shield, on battery (Fig. 13). (11) Install battery cables on battery. Securely
tighten clamping bolts on battery cable terminals. (12) Reset any electrical components of the vehicle
which were affected by the removal of the battery. (13) Road test vehicle to verify correct operation of
the vehicles's base and Antilock brake systems.
ELECTRONIC COMPONENTS
CONTROLLER ANTILOCK BRAKE CAB
REMOVE
(1) Turn vehicle ignition off.
(2) Disconnect the wiring harness connector from
the Antilock system relay (Fig. 1). Relay will be re-
moved as part of the CAB bracket.
CAUTION: BEFORE REMOVING 60 WAY CONNEC-
TOR FROM THE CAB VERIFY THAT THE VEHICLE'S
IGNITION IS IN THE OFF OR LOCK POSITION. IF IG-
NITION IS ON WHEN 60 WAY CONNECTOR IS RE-
MOVED FROM THE CAB DAMAGE TO THE
CONTROLLER COULD OCCUR.
(3) Loosen bolt (Fig. 2) retaining the wiring har-
ness 60 way connector to the CAB. Then disconnect
the 60 way connector (Fig. 2) from the CAB by pull-
ing it straight out, do not twist connector when re-
moving. (4) Remove the 2 bolts (Fig. 3) attaching the CAB
module mounting bracket, to the frame rail of the ve-
hicle. (5) Remove the CAB and its mounting bracket as
an assembly from the vehicle from the vehicle. (6) Remove the 3 screws (Fig. 4) attaching the
CAB to the CAB mounting bracket. Then separate
CAB from mounting bracket.
Fig. 11 Vacuum Reservoir Installation And Attaching Bolts
Fig. 12 Battery Tray Access Shield Installed
Fig. 13 Battery Hold Down Clamp And Heat Shield Installed
Fig. 1 CAB Location
Ä ANTILOCK 4 BRAKE SYSTEM 5 - 41

INSTALL (1) Install CAB and system relay/bracket assembly
on CAB mounting bracket (Fig. 4). Install the 3 CAB
to CAB mounting bracket attaching screws (Fig. 4). Torque the 3 CAB to mounting bracket attaching
screws to 12 N Im (106 in. lbs.).
(2) Install the CAB, system relay and mounting
bracket on the frame rail of the vehicle. Install the 2
bolts (Fig. 3) attaching the CAB mounting bracket to
the frame rail of the vehicle. Torque the 2 CAB mount-
ing bracket attaching bolts (Fig. 3) to 28 N Im (250 in.
lbs.).
CAUTION: BEFORE INSTALLING 60 WAY CONNEC-
TOR ON THE CAB VERIFY THAT THE VEHICLE'S
IGNITION IS IN THE OFF OR LOCK POSITION. IF
IGNITION IS ON WHEN 60 WAY CONNECTOR IS
INSTALLED ON THE CAB, DAMAGE TO THE CON-
TROLLER COULD OCCUR.
(3) Install the wiring harness 60 way connector (Fig.
2) into the CAB electrical connector as far as possible
by hand. After 60 way connector is installed as far as
possible by hand, use the 60 way connector retaining
bolt (Fig. 2) to fully seat connector into the CAB. Then
torque the wiring harness 60 way CAB connector
retaining bolt to 4 N Im (38 in. lbs.).
(4) Install the wiring harness connector onto the
Antilock system relay (Fig. 1). Be sure locking tab
on wiring harness connector is fully engaged
with lock on system relay. (5) Road test vehicle to verify correct operation of the
vehicles's Antilock brake system.
REMOVAL/INSTALLATION OF SYSTEM RELAY
The antilock brake system, system relay is serviced
as an assembly, with the mounting bracket. The sys-
tem relay is mounted to a separate bracket which is
attached to the CAB and mounting bracket assembly
(Fig. 5).
Fig. 2 CAB 60 Way Connector And Retaining Bolt
Fig. 3 CAB Bracket To Frame Rail Mounting Bolts
Fig. 4 CAB Removal From Mounting Bracket
Fig. 5 Antilock Brakes System Relay Location
5 - 42 ANTILOCK 4 BRAKE SYSTEM Ä

REMOVE (1) Hold system relay with one hand, while pulling
strait down on the wiring harness connector. Until
connector is free from the relay (do not twist the
connector). (2) Remove screw (Fig. 6) holding the system relay
and bracket to the CAB bracket. Then remove the
system relay and mounting bracket assembly from
the CAB bracket.
INSTALL (1) Mount the system relay and its mounting
bracket assembly to the CAB mounting bracket, with
the mounting screw (Fig. 6). (2) Holding the system relay with one hand, push-
ing the wiring harness connector strait onto the ter-
minals of the relay. Make sure connector is fully
seated onto terminals of the system relay and the
lock on the wiring harness connector is fully engaged
with the relay. (3) Road test vehicle to verify correct operation of
the vehicles's Antilock brake system.
REMOVE/INSTALL PUMP MOTOR RELAY
Find location of Antilock Pump Motor Relay (Fig. 7
& 8), depending on whether the vehicle being ser-
viced has or does not have a power distribution cen-
ter PDC. (1) Hold the Antilock pump motor relay with one
hand, while pulling wiring harness relay connector
strait off the relay terminals. (2) Remove the pump motor relay assembly from
the vehicle. (3) Installation is done in the reverse order off re-
moval. Be sure that the wiring harness connector is
fully seated onto the terminals of the Pump Motor
Relay.
WHEEL SPEED SENSORS
INSPECTION
Inspect tonewheel for missing or broken teeth, this
can cause erratic sensor signals. Tonewheel should show no evidence of contact with
the wheel speed sensor. If contact was made, deter-
mine cause and correct. Excessive runout of the tonewheel can cause er-
ratic wheel speed sensor. Replace assembly if runout
exceeds approximately 0.25 mm (0.010 inch).
FRONT WHEEL SPEED SENSOR (FIG. 9)
REMOVAL
(1) Raise vehicle and remove wheel and tire as-
sembly. (2) Remove screw from grommet retainer clip that
holds the grommet into fender shield (Fig. 9). (3) Remove the 2 screws that fasten the sensor
routing tube to the frame rail.
Fig. 6 System Relay And Bracket Removal
Fig. 7 Pump Motor Relay Location On AA Body W/O Power Distribution Center
Fig. 8 Pump Motor Relay Location On AJ Body WithPower Distribution Center
Ä ANTILOCK 4 BRAKE SYSTEM 5 - 43