1993 CHEVROLET PLYMOUTH ACCLAIM ignition

to the rear will be lower than the front brakes. This will
prevent premature rear wheel lock-up and skid. If
hydraulic pressure is lost in one half of the diagonally
split system, the operation of the proportioning valve
in the remaining half is not effected.
ABS BRAKE PROPORTIONING VALVE OPERATION
On vehicles using the ABS braking system, screw in
proportioning valves are used in place of the conven-
tional differential pressure/proportioning valve. Each rear brake circuit has its own screw-in propor-
tioning valve which is attached to the rear brake outlet
ports of the hydraulic assembly. These valves limit
brake pressure to the rear brakes after a certain
pressure is reached. This improves front to rear brake
balance during normal braking.
Screw in proportioning valves can be identified by
the numbers stamped on the body of the valve. The
first digit represents the slope, the second digit repre-
sents the split (cut-in) point, and the arrow represents
the flow direction of the valve. Be sure that the
numbers listed on the replacement valve are the
same as on the valve that is being removed. See
(Fig. 3) for detail of the valve identification.
HYDRAULIC SYSTEM SERVICE PROCEDURES
BRAKE WARNING SYSTEM
CHECKING BRAKE WARNING SWITCH UNIT
The Red Brake Warning light will come on when
the parking brake is applied with the ignition key
turned ON. The same light will also illuminate
should one of the two service brake hydraulic sys-
tems fail.
CAUTION:Make sure air does not enter the hydrau-
lic system during this test procedure. See bleeding
without a pressure bleeder at the beginning of this
section for master cylinder fluid level checking pro-
cedures.
To test the service brake warning system lamp.
Raise the vehicle on a hoist and open a wheel cylin-
der bleeder while a helper depresses the brake pedal
and observes the warning light. If the light fails to light, inspect for a burned out
bulb, disconnected socket, or a broken or discon-
nected wire at the switch. If the bulb is not burned
out and the wire continuity is uninterrupted. Check
the service brake warning switch operation with a
test lamp between the switch terminal and a known
good ground. Be sure to fill master cylinder and
bleed brake system after correction has been made, if
necessary.
PROPORTIONING VALVES
TESTING PROPORTIONING VALVE UNIT
If premature rear wheel skid occurs on hard brake
application, it could be an indication that a malfunc-
tion has occurred with the proportioning valve unit. The proportioning valve is designed with two sep-
arate systems. One half controls the right rear
brake, and the other half controls the left rear brake.
Therefore, a road test to determine which rear brake
slides first is essential.
RIGHT REAR WHEEL SLIDES FIRST To test the proportioning valve when the right rear
wheel slides first, leave the front brakes connected to
the valve, proceed as follows: (1) Install one gauge and (TEE) of set C-4007-A
between the brake line from the master cylinder sec-
ondary port and the brake valve assembly. (2) Install the second gauge of set C-4007-A to the
right rear brake outlet port (Fig. 4). Using an
adapter tube, made from a short piece of brake tube
and (2) 3/8 x 24 tube nuts. Connect the hose to the
valve. Bleed the hose and gauge. (3) Have a helper exert pressure on the brake
pedal (holding pressure) to get a reading on the valve
inlet gauge and check the reading on the outlet
Fig. 3 ABS PROPORTIONING VALVE IDENTIFICA- TION
Ä BRAKES 5 - 27

MASTER CYLINDER INDEX
page page
Brake Fluid Level Sensor .................. 66
General Information ....................... 66 Master Cylinder Service Procedures
.......... 67
Testing the Master Cylinder ................. 66
GENERAL INFORMATION
The tandem master cylinder (Fig. 1) has a glass re-
inforced nylon reservoir and an anodized aluminum
body. Do not hone the bore of the cylinder, as this will
remove the anodized surface. The reservoir is indexed to prevent installation in
the wrong direction (Fig. 2). The cap diaphragms are
slit to allow atmospheric pressure to equalize on both
sides of the diaphragm. The primary and secondary outlet tubes from the
master cylinder are connected to the valve mounted
under the master cylinder. The front part of this
block connects to the secondary outlet tube and sup-
plies the right rear and left front brakes. The rear
portion of the block connects to the primary outlet
tube and supplies the right front and left rear
brakes.
BRAKE FLUID LEVEL SENSOR
The Brake Fluid Level sensor is found only in the
AJ body vehicles with the visual electronic message
center. The purpose of the sensor is to provide the
driver with an early warning message that brake
fluid in master cylinder reservoir has dropped to a
below normal. As the fluid drops below the design level the sensor
closes the warning message circuit. Approximately
15 seconds later the message BRAKE FLUID LOW
appears on the instrument panel. At this time the master cylinder reservoir should be checked and filled
to the bottom of the rings with DOT 3 brake fluid. To check the operation of the Brake Fluid Level
sensor, with ignition on and wiring still attache-
d,remove sensor from master cylinder and hold in
upright position. Within 30 seconds the instrument
panel message BRAKE FLUID LOW should appear.
Next invert the sensor. The instrument panel message
should turn off immediately. If the above sequence
occurs the sensor is operating properly. If the message
does not appear remove the wiring from the sensor and
using a jumper wire connect both sides of the plug. The
instrumental panel message BRAKE FLUID LOW
should appear within 30 seconds. If the message does
not appear a problem exists in the wiring or instru-
mentation. If the message does appear the sensor is
faulty and must be replaced. The Brake Fluid Level
sensor is not a repairable item (Fig. 2).
TESTING THE MASTER CYLINDER
Be sure master cylinder vents at both ports.
Apply pedal lightly with engine running and look for
fluid squirting or swirling into reservoirs. In this master cylinder, a special baffle reduces the
amount of fluid entering the secondary reservoir only a
small disturbance may be seen.
Fig. 1 Aluminum Master Cylinder (Cutaway View)
Fig. 2 Brake Fluid Level Sensor
5 - 66 BRAKES Ä

ABS EQUIPPED VEHICLE PERFORMANCE
Anti-Lock 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. Hydroplaning
results in the vehicle tires leaving the road surface
rendering the vehicle almost uncontrollable. In addi-
tion, extreme steering maneuvers at high speed or
high speed cornering beyond limits of tire adhesion
to the road surface may cause vehicle skidding. So,
the ABS system is termed Anti-Lock instead of Anti-
Skid. One of the significant benefits of the ABS system is
that of maintaining steering control during hard
braking or during braking on slippery surfaces. It is
therefore possible to steer the vehicle while braking
on almost any road surface.
ABS SYSTEM SELF-DIAGNOSTICS
The ABS system has been designed with Self Diag-
nostic Capability. There are two self checks the sys-
tems performs every time the vehicle is started.
First, when the key is turned on the system performs
an electrical check called Start-Up Cycle. During this
check, the Red Brake Warning Lamp and the Amber
Anti-Lock Warning Lamp are illuminated. Then
turned off at the end of the test, after about 1 to 2
seconds. When the vehicle reaches a speed of about 3
to 4 miles per hour. The system performs a func-
tional check called Drive-Off. During Drive-Off. hy-
draulic valves are activated briefly to test their
function. Drive-Off can be detected as a series of
rapid clicks upon driving off the first time the car is
started. If the brake pedal is applied during Drive-
Off, the test is by-passed. Both of these conditions
are a normal part of the system self test. Most fault
conditions will set a ABS Fault Code in the (CAB),
which can be retrieved to aid in fault diagnosis. De-
tails can be found in Diagnosis Section.
ABS WARNING SYSTEMS OPERATION
The ABS system uses two methods for notifying
the driver of a system malfunction. These include the
standard Red Brake Warning Lamp and an Amber
Anti-Lock Warning Lamp, both located in the instru-
ment cluster. The purpose of these two lamps are dis-
cussed in detail below.
RED BRAKE WARNING LAMP
The Red Brake Warning Lamp, located in the in-
strument cluster, will Turn On to warn the driver of
brake system conditions that may result in reduced
braking ability. The lamp is also turned on when the
parking brake is not fully released. Conditions which
may cause the Red Brake Warning Lamp to Turn On
include: ²
Parking brake not fully released. If the parking
brake is applied or not fully released. The switch on the
parking brake pedal assembly will ground the Red
Brake Warning Lamp circuit and cause the lamp to
turn on. On vehicles equipped with mechanical instru-
ment clusters, the Amber Anti-Lock Lamp will turn on
if the vehicle is driven above 3 miles per hour with the
Parking Brake applied.
² Low brake fluid. The fluid level sensor in the hy-
draulic assembly reservoir will ground the Red Brake
Warning Lamp circuit if low brake fluid level is de-
tected. In addition, ABS will be deactivated above 3
miles per hour and the Amber Anti-Lock Warning
Lamp will be illuminated. If the vehicle is equipped
with EVIC, a low fluid condition will also cause the
Low Brake Fluid message to appear.
² Low Accumulator Pressure. In the event of low
accumulator pressure, the dual function pressure
switch in the hydraulic assembly will signal the (CAB)
to ground the Red Brake Warning Lamp circuit. This
will cause the Red Brake Warning Lamp to turn on.
Low accumulator pressure also results in the activa-
tion of the Yellow Anti-Lock Warning Lamp. Low accu-
mulator pressure may result in loss of power assist.
² Modulator Or (CAB) Faults. The modulator assem-
bly or (CAB) may turn on the Yellow Anti-Lock Warn-
ing Lamp, if certain faults are detected in either the
modulator assembly or the (CAB).
² Bulb check. As a bulb check, the Red Brake Warning
Lamp will illuminate whenever the ignition switch is
placed in the crank position. Illumination of the red Brake Warning Lamp
may indicate reduced braking ability. A vehicle
that has the Red Brake Warning Lamp ON should
not be driven except to do diagnostic procedures
described in Section 2 of this manual. Most con-
ditions that turn on the Red Brake Warning
Lamp will also turn on the Amber Anti-Lock
Warning Lamp, consequently disabling the Anti-
Lock function.
ANTI-LOCK WARNING LAMP
The Anti-Lock Warning Lamp is located in the in-
strument cluster and is Amber in color. The Amber
Anti-Lock Warning Lamp is illuminated when the
(CAB) detects a condition that results in a shutdown of
Anti-Lock function. The Amber Anti-Lock Warning
Lamp is normally on until the (CAB) completes its self
tests and turns the lamp off. For example, if the (CAB)
is disconnected, the lamp is on. Display of the Amber Anti-Lock Warning Lamp
without the Red Brake Warning Lamp indicates
only that Anti-Lock function has been disabled.
Power assisted normal braking is unaffected.
Ä ANTI-LOCK 10 BRAKE SYSTEM 5 - 75

NORMAL OPERATION OF WARNING LAMPS
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 turn on
for as little as 1 second to as long as 30 seconds. If the car has not been started for several hours,
for example after sitting overnight. The Red Brake
Warning Lamp and the Amber Anti-Lock Warning
Lamp may both be turned on for as long as 60 sec-
onds after turning the ignition on. This condition is
caused by the loss of accumulator charge when the
vehicle is parked for extended periods, particularly in
cold weather. When the key is then turned on. The
Pump/Motor assembly must recharge the hydraulic
accumulator to its normal operating pressure. As re-
charging is completed, both warning lamps will turn
off when accumulator pressure reaches about (1,000
psi). Both lamps should remain off at all other times,
indicating normal operation.
ANTI-LOCK BRAKE SYSTEM COMPONENTS
The following is a detailed description of the Anti-
Lock Brake System components. For information on
servicing the other Non-ABS related components
that may be referred to in this section. See the Stan-
dard Brakes Section that refers to the specific com-
ponent.
HYDRAULIC ASSEMBLY
The ABS system uses an integral Hydraulic Assem-
bly (Fig. 1). The hydraulic assembly includes a
Booster/Master Cylinder, Modulator, Hydraulic Blad-
der Accumulator and Fluid Reservoir. The Hydraulic
Assembly is located on the dash panel cowl on the
drivers side of the vehicle. The following is a descrip-
tion of the components that make up the Hydraulic
Assembly.
HYDRAULIC ASSEMBLY BRAKE FLUID RES- ERVOIR
A one piece Fluid Reservoir is attached to the hy-
draulic assembly with rubber seals. The Fluid Reser-
voir (Fig. 1) is internally separated into three fluid
sections. Most of the brake fluid is contained in the
Fluid Reservoir and hydraulic bladder accumulator
(Fig. 1). Additional fluid is contained in the
pump/motor assembly accumulator.
BOOSTER/MASTER CYLINDER
The Booster/Master Cylinder portion of the
hydraulic assembly is an integral component and
should never be disassembled. The Booster/Master Cylinder uses a diagonally split
configuration during normal braking. The two
Fig. 1 Hydraulic Assembly
5 - 76 ANTI-LOCK 10 BRAKE SYSTEM Ä

stant velocity joint housings. The rear Tone Wheels
are serviced as an assembly with the rear disc brake
rotor hub. Correct Anti-Lock System operation is dependent
on wheel speed signals from the wheel speed sensors.
The vehicles' wheels and tires must all be the same
size and type to generate accurate signals. In addi-
tion, the tires must be inflated to the recommended
pressures for optimum system operation. Variations
in wheel and tire size or significant variations in in-
flation pressure can produce inaccurate wheel speed
signals.
CONTROLLER ANTI-LOCK BRAKE (CAB)
The Anti-Lock Brake Controller is a small micro-
processor based device that monitors the brake sys- tem and controls the system while it functions in
Anti-Lock Mode. The CAB is located under the bat-
tery tray and is mounted to the left frame rail (Fig.
7) and uses a 60-way system connector. The power
source for the CAB is through the ignition switch to
pin 60 of the controller. With the ignition in the
RUN or ON position. IF THE (ABS) CONTROL-
LER NEEDS TO BE REPLACED BE SURE THE
CORRECT CONTROLLER IS USED. THE CON-
TROLLER ANTI-LOCK BRAKE (CAB) IS NOT
ON THE CCD BUS
Fig. 5 Rear Wheel Speed Sensor
Fig. 4 Front Wheel Speed Sensor
Fig. 6 Rear Tone Wheel
Fig. 7 Location Controller Anti-Lock Brake (CAB)
5 - 80 ANTI-LOCK 10 BRAKE SYSTEM Ä

The primary functions of the (CAB) are:
² (1) Detect wheel locking tendencies.
² (2) Control fluid modulation to the brakes while in
Anti-Lock mode.
² (3) Monitor the system for proper operation.
² (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 wheel locking tendency is de-
tected, 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 or Decay valves to modulate brake
fluid pressure in some or all of the hydraulic circuits.
The fluid used for modulation comes from the booster
servo circuit. The (CAB) continues to control pres-
sure in individual hydraulic 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 can disable the Anti-Lock braking function.
Depending on the fault, the (CAB) will light one or
both of the brake warning lamps. The (CAB) contains a System Diagnostic Program
which triggers the brake system warning lamps
when a system fault is detected. Faults are stored in
a diagnostic program memory. There are 19 fault
codes that 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. These fault codes will remain in memory
until they are cleared with the DRB II, or automati-
cally erased from the memory after (50) ignition
switch on/off cycles.
CONTROLLER ANTI-LOCK BRAKE (INPUTS)
² Four wheel speed sensors.
² Boost pressure transducer.
² Primary pressure transducer.
² Low fluid level switch.
² Differential pressure switch.
² Parking brake switch.
² Dual function pressure switch (warning pressure
only)
² Stop lamp switch.
² Ignition switch.
² System relay voltage.
² Ground.
² Low Accumulator
CONTROLLER ANTI-LOCK BRAKE (OUTPUTS)
²Ten modulator valves-3 decay, 3 build and 4 isola-
tion.
² Red Brake warning lamp.
² Amber Anti-Lock Warning Lamp.
² System relay actuation. ²
Diagnostic communication.
ABS SYSTEM DIAGNOSTIC CONNECTOR
The Bendix Anti-Lock system diagnostic connector
is located under the lower dash panel or in the area
of the fuse box (Fig. 8). The fuse box is located be-
hind the access panel that is on the bottom portion of
the dash panel, left of the steering column. The diag-
nostics connector is a blue 6 way connector.
ANTI-LOCK SYSTEM RELAYS AND WARNING
LAMPS
PUMP/MOTOR RELAY
Pump/Motor power is supplied by the Pump/Motor
Relay. The Pump/Motor relay is located inside the
Power Distribution Center (PDC). The relay coil is
energized by a ground from the Dual Function Pres-
sure Switch. See (Fig. 9) for the location of the pump/
motor relay in the (PDC).
SYSTEM RELAY
The (ABS) Modulator Valves and Anti-Lock Warn-
ing Lamp Relay are controlled through a System Re-
lay. The System relay is located on the top left inner
fender behind the headlight (Fig. 10). The system re-
lay provides power to the (CAB) for modulator valve
operation (pins 47 and 50) after the start-up cycle
when the ignition is turned on.
ANTI-LOCK WARNING LAMP RELAY
The Anti-Lock Warning Lamp is controlled by the
Yellow Light Relay. See (Fig. 10) for location behind
the left headlight. With the relay de-energized, the
lamp is lit. When the system relay is energized by
Fig. 8 A.B.S. Diagnostic Connector Location
5 - 82 ANTI-LOCK 10 BRAKE SYSTEM Ä

In order to effectively diagnose an Anti-Lock Brake
System (ABS) condition. It is important to read Sec-
tion 1 of this manual, Anti-Lock Brake System De-
scription. This section will give you information on
the function of the ABS components. Then follow the
diagnostic procedures outlined in this section. Many conditions that generate customer com-
plaints of the ABS system may be normal operating
conditions. These conditions though are judged to be
a problem due to unfamiliarity with the ABS system.
These conditions can be recognized without perform-
ing extensive diagnostic work, given adequate under-
standing of operating principles and performance
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 CONTROLLER ANTI-LOCK BRAKE (CAB) SER-
VICE 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 appropriate diagnostic pro-
cedure. 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 position. Before removing or
connecting battery cables, fuses, or connectors, always
turn the ignition to the OFF position.
ABS SYSTEM 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. Before test driving a brake complaint vehicle,
especially if the Red Brake Warning Lamp is on.
Test the brake function at low speed to be sure
that the car will stop normally. Remember that
conditions that result in illumination of the Red
Fig. 14 Decay Pressure - Hydraulic Control
5 - 88 ANTI-LOCK 10 BRAKE SYSTEM Ä

Brake Warning Lamp may indicate reduced
braking ability. The following procedure should
be used to test drive an ABS complaint:(1) Ignition on. Turn the ignition to the ON position
without starting the car and wait until the Red Brake
Warning Lamp and Amber Anti-Lock Warning Lamp
turn off. This will allow the pump to charge the
accumulator to operating pressure. If the warning
lamp(s) do not turn off, go to step 3. (2) Ignition off for 15 seconds.
(3) Start car. Wait for displays to return to normal
operating mode before proceeding. (4) With Shift lever in PARK, slowly depress brake
pedal and release. (5) Drive vehicle a short distance. During this test
drive, be sure that the vehicle achieves at least 20 mph.
Then brake to at least one complete stop and accelerate
slowly back up to at least 20 mph. (6) If a functional problem with the A.B.S. system is
determined while test driving a vehicle. Refer to the
Bendix Anti-Lock 10 Diagnostics Manual for required
test procedures and proper use of the DRB II tester.
CAUTION: The following are general precautions that
should be observed when servicing and diagnosing
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 the vehicle
using an arc welder, the (CAB) should be disconnected
before the welding operation begins. (2) The (CAB) and hydraulic assembly 10 way con-
nectors should never be connected or disconnected with
the ignition on. (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. (4) Always de-pressurize the Hydraulic Accu-
mulator when performing any work that re-
quires disconnecting any hydraulic tube, flex
hose or fitting. The ABS system uses brake fluid
at high pressure. Failure to de-pressurize the
accumulator may result in personal injury
and/or damage to painted surfaces. Brake fluid will damage painted surfaces. If brake
fluid is spilled on any painted surfaces, wash off with
water immediately.
DE-PRESSURIZING HYDRAULIC ACCUMULA- TOR
The ABS pump/motor assembly keeps the hydraulic
accumulator charged between approximately 11,032
and 13,790 kPa (1600 and 2000 psi) anytime key is in the ON position. The pump/motor assembly
cannot run if the ignition is off or either battery ca-
ble is disconnected. Unless otherwise specified, the hydraulic accumu-
lator should be de-pressurized before disassembling
any portion of the hydraulic system. The following
procedure should be used to de-pressurize the hy-
draulic accumulator: (1) With ignition off, or either battery cable discon-
nected, pump the brake pedal a minimum of 40 times
using approximately 50 pounds of pedal force. A no-
ticeable change in pedal feel will occur when the ac-
cumulator becomes discharged. (2) When a definite increase in pedal effort is felt,
pump the pedal a few additional times. This will in-
sure removal of all hydraulic pressure from the
brake system.
WHEEL SPEED SENSOR CABLES
Proper installation of wheel speed sensor cables is
critical to continued ABS system operation. Be sure
that cables are installed and routed properly. Failure
to install cables in their retainers, as shown in Sec-
tion 3 of this manual. May result in contact with
moving parts or over extension of cables, resulting in
an open circuit.
MECHANICAL DIAGNOSTICS AND SERVICE
PROCEDURES
SPECIAL SERVICE TOOLS
Some diagnostic procedures in this section require
the use of special service tools. Each of these tools is
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 diag-
nostics are performed. Refer to those sections for
proper testing procedures and the DRB II manual for
its proper operational information.
MST-6163 PRESSURE TESTER
Some diagnostic procedures in this manual require
the use of the MST-6163 pressure gauge and adaptor
(Fig. 2). Pressure Gauge, Special Tool MST-6163 is
required to measure accumulator pressure during
certain phases of ABS operation. The pressure gauge
and adaptor should be installed as follows: (1) De-pressurize the accumulator by pumping the
brake pedal a minimum of 40 times with the ignition
off. The procedure is fully explained under De-Pres-
surizing Hydraulic Accumulator which is described
earlier in this System Diagnosis Section.
Ä ANTI-LOCK 10 BRAKE SYSTEM 5 - 89