Chrysler Stratus Convertible. Manual - part 203

to prevent wheel lockup under braking conditions on
virtually any type of road surface. Antilock braking is
desirable because a vehicle that is stopped without
locking the wheels retains directional stability and
some steering capability. This allows the driver to
retain greater control of the vehicle during braking.

OPERATION

There are a few performance characteristics of the

Mark 20i Antilock Brake System that may at first
seem abnormal, but in fact are normal. These char-
acteristics are described below.

NORMAL BRAKING

Under normal braking conditions, the ABS func-

tions the same as a standard base brake system with
a diagonally split master cylinder and conventional
vacuum assist.

ABS BRAKING

ABS operation is available at all vehicle speeds

above 3–5 mph. If a wheel locking tendency is
detected during a brake application, the brake sys-
tem enters the ABS mode. During ABS braking,
hydraulic pressure in the four wheel circuits is mod-
ulated to prevent any wheel from locking. Each
wheel circuit is designed with a set of electric sole-
noids to allow modulation and each wheel receieves
its own separate electrical signal. Wheel lockup may
be perceived at the very end of an ABS stop and is
considered normal.

During an ABS stop, the brakes hydraulic system

is still diagonally split. However, the brake system
pressure is further split into four control channels.
During antilock operation of the vehicle’s brake sys-
tem, the front wheels are controlled independently
and are on two separate control channels, and the
rear wheels of the vehicle are controlled together.

BRAKES

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The system can build and release pressure at each

wheel, depending on signals generated by the wheel
speed sensors (WSS) at each wheel and received at
the controller antilock brake (CAB).

NOISE AND BRAKE PEDAL FEEL

During ABS braking, some brake pedal movement

may be felt. In addition, ABS braking will create
ticking, popping, or groaning noises heard by the
driver. This is normal and is due to pressurized fluid
being transferred between the master cylinder and
the brakes. If ABS operation occurs during hard
braking, some pulsation may be felt in the vehicle
body due to fore and aft movement of the suspension
as brake pressures are modulated.

At the end of an ABS stop, ABS is turned off when

the vehicle is slowed to a speed of 3–4 mph. There
may be a slight brake pedal drop anytime that the
ABS is deactivated, such as at the end of the stop
when the vehicle speed is less than 3 mph or during
an ABS stop where ABS is no longer required. These
conditions exist when a vehicle is being stopped on a
road surface with patches of ice, loose gravel, or sand
on it. Also, stopping a vehicle on a bumpy road sur-
face activates ABS because of the wheel hop caused
by the bumps.

TIRE NOISE AND MARKS

Although the ABS system prevents complete wheel

lockup, some wheel slip is desired in order to achieve
optimum braking performance. Wheel slip is defined
as follows: 0 percent slip means the wheel is rolling
freely and 100 percent slip means the wheel is fully
locked. During brake pressure modulation, wheel slip
is allowed to reach up to 25–30 percent. This means
that the wheel rolling velocity is 25–30 percent 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 lockup.

Complete wheel lockup normally leaves black tire

marks on dry pavement. The ABS will not leave dark
black tire marks since the wheel never reaches a
fully locked condition. However, tire marks may be
noticeable as light patched marks.

START-UP CYCLE

When the ignition is turned on, a popping sound

and a slight brake pedal movement may be noticed.
The ABS warning lamp will also be on for up to 5
seconds after the ignition is turned on. When the
vehicle is first driven off, a humming may be heard
or felt by the driver at approximately 25–40 kph
(15–25 mph). All of these conditions are a normal
function of ABS as the system is performing a diag-
nosis check.

PREMATURE ABS CYCLING

Symptoms of premature ABS cycling include: click-

ing sounds from the solenoid valves; pump/motor
running; and pulsations in the brake pedal. Prema-
ture ABS cycling can occur at any braking rate of the
vehicle and on any type of road surface. Neither the
red BRAKE warning lamp, nor the amber ABS warn-
ing lamp, illuminate and no fault codes are stored in
the CAB.

Premature ABS cycling is a condition that needs to

be correctly assessed when diagnosing problems with
the antilock brake system. It may be necessary to use
a DRB scan tool to detect and verify premature ABS
cycling.

Check the following common causes when diagnos-

ing premature ABS cycling: damaged tone wheels;
incorrect tone wheels; damaged steering knuckle
wheel speed sensor mounting bosses; loose wheel
speed sensor mounting bolts; excessive tone wheel
runout; or an excessively large tone wheel-to-wheel
speed sensor air gap. Give special attention to these
components when diagnosing a vehicle exhibiting
premature ABS cycling.

After diagnosing the defective component, repair or

replace it as required. When the component repair or
replacement is completed, test drive the vehicle to ver-
ify that premature ABS cycling has been corrected.

ANTILOCK BRAKE SYSTEM COMPONENTS

The following is a detailed description of the

antilock brake system components. For information
on servicing base brake system components used in
conjunction with these components, see the BASE
BRAKE SYSTEM found at the beginning of this ser-
vice manual group.

MASTER CYLINDER

DESCRIPTION

A vehicle equipped with ABS uses a different mas-

ter cylinder (Fig. 1) than a vehicle that is not
equipped with ABS. Vehicles equipped with ABS use
a center port master cylinder while vehicles not
equipped with ABS use a compensating port master
cylinder.

The brake tubes from the primary and secondary

outlet ports on the master cylinder go directly to the
hydraulic control unit (HCU).

The power brake booster used on a vehicle

equipped with ABS is the same as a vehicle not
equipped with ABS.

Refer to the BASE BRAKE SYSTEM at the begin-

ning of this service manual group for further infor-
mation and procedures on master cylinders.

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BRAKES

DESCRIPTION AND OPERATION (Continued)

When the brake pedal in depressed, the master cyl-

inder primary and secondary pistons apply brake
pressure through the chassis brake tubes, ABS
hydraulic control unit, and proportioning valves to
each brake assembly. On ABS master cylinders, the
primary outlet port supplies hydraulic pressure to
the right front and left rear brakes. The secondary
outlet port supplies hydraulic pressure to the left
front and right rear brakes.

Refer to the BASE BRAKE SYSTEM at the begin-

ning of this service manual group for further infor-
mation.

OPERATION

When the brake pedal in depressed, the master cyl-

Refer to the BASE BRAKE SYSTEM at the begin-

ning of this service manual group for further infor-
mation.

INTEGRATED CONTROL UNIT (ICU)

DESCRIPTION

The hydraulic control unit (HCU) and the control-

ler antilock brake (CAB) used with this antilock
brake system are combined (integrated) into one
unit, which is called the integrated control unit (ICU)
(Fig. 2). The ICU is located on the passenger’s side of

the vehicle, and is mounted on top of the front sus-
pension crossmember (Fig. 3). It can be accessed from
under the vehicle.

Two different HCU’s and CAB’s are used on this

vehicle depending on whether or not the vehicle is
equipped with traction control. The HCU on a vehicle

Fig. 1 Master Cylinder

1 – POWER BRAKE VACUUM BOOSTER
2 – MASTER CYLINDER FLUID RESERVOIR
3 – MASTER CYLINDER BODY

Fig. 2 Integrated Control Unit (ICU)

1 – HCU
2 – PUMP/MOTOR
3 – CAB

Fig. 3 ICU Mounting Location

1 – POWER STEERING PULLEY
2 – ENGINE CRANKSHAFT PULLEY
3 – ENGINE OIL PAN
4 – CAB CONNECTOR
5 – CONTROLLER ANTILOCK BRAKE (CAB)
6 – RIGHT HALF SHAFT
7 – PUMP MOTOR

BRAKES

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DESCRIPTION AND OPERATION (Continued)

equipped with ABS and traction control has a valve
block housing that is approximately 1 inch longer on
the low pressure fluid accumulators side than a HCU
on a vehicle that is equipped with only ABS.

The ABS-only ICU consists of the following compo-

nents: the CAB, eight (build/decay) solenoid valves
(four inlet valves and four outlet valves), valve block,
fluid accumulators, a pump, and an electric motor.

The ABS-with traction control ICU consists of the

following components: the CAB, eight (build/decay)
solenoid valves (four inlet valves and four outlet
valves), two hydraulic shuttle valves, two ASR
valves, valve block, fluid accumulators, a pump, and
an electric pump/motor. On vehicles with traction
control, the ICU contains 10 solenoid valves. The two
ASR valves and solenoids are used to isolate the
brake system during traction control operation.

The replaceable components of the ICU are the

HCU and the CAB. No attempt should be made to
service any individual components of the HCU or
CAB.

OPERATION

For information on the operation of the ICU, refer

to the individual components:

• CONTROLLER ANTILOCK BRAKE (CAB)

• HYDRAULIC CONTROL UNIT (HCU)
For information on the ICU’s hydraulic circuits,

refer

HYDRAULIC

CIRCUITS

AND

VALVE

OPERATION which can be found elsewhere in this
section.

CONTROLLER ANTILOCK BRAKE (CAB)

DESCRIPTION

The controller antilock brake (CAB) is a micropro-

cessor-based device which monitors the ABS system
during normal braking and controls it when the vehi-
cle is in an ABS stop. The CAB is mounted to the
bottom of the HCU (Fig. 2). The CAB uses a 25-way
electrical connector on the vehicle wiring harness.
The power source for the CAB is through the ignition
switch in the RUN or ON position. The CAB is on
the CCD bus.

OPERATION

The primary functions of the CAB are to:
(1) monitor the antilock brake system for proper

operation.

(2) detect wheel locking or wheel slipping tenden-

cies by monitoring the speed of all four wheels of the
vehicle.

(3) control fluid modulation to the wheel brakes

while the system is in an ABS mode or the traction
control system is activated.

(4) store diagnostic information.
(5) provide communication to the DRB scan tool

while in diagnostic mode.

The CAB constantly monitors the antilock brake

system for proper operation. If the CAB detects a
fault, it will turn on the amber ABS warning lamp
and disable the antilock braking system. The normal
base braking system will remain operational.

The CAB continuously monitors the speed of each

wheel through the signals generated by the wheel
speed sensors to determine if any wheel is beginning
to lock. When a wheel locking tendency is detected,
the CAB actuates its solenoids. This actuation opens
and closes the valves in the HCU thereby modulating
brake fluid pressure in the hydraulic circuits. The
CAB continues to control pressure in individual
hydraulic circuits until a locking tendency is no
longer present.

The CAB contains a self-diagnostic program that

monitors the antilock brake system for system faults.
When a fault is detected, the amber ABS warning
lamp is turned on and the fault diagnostic trouble
code (DTC) is then stored in a diagnostic program
memory. These DTC’s will remain in the CAB mem-
ory even after the ignition has been turned off. The
DTC’s can be read and cleared from the CAB mem-
ory by a technician using the DRB scan tool. If not
cleared with a DRB scan tool, the fault occurrence
and DTC will be automatically cleared from the CAB
memory after the identical fault has not been seen
during the next 3,500 miles.

CONTROLLER ANTILOCK BRAKE INPUTS

• wheel speed sensors (four)

• stop lamp switch

• ignition switch

• system voltage

• ground

• traction control switch (if equipped)

• diagnostic communication (CCD)

CONTROLLER ANTILOCK BRAKE OUTPUTS

• amber ABS warning lamp actuation

• instrument cluster (MIC)

• traction control lamps (if equipped)

• diagnostic communication (CCD)

HYDRAULIC CONTROL UNIT (HCU)

DESCRIPTION

The hydraulic control unit (HCU) is mounted to

the CAB as part of the ICU (Fig. 4). The ICU is
located on the passenger’s side of the vehicle, and is
mounted on top of the front suspension crossmember
(Fig. 3). It can be accessed from under the vehicle.

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BRAKES

DESCRIPTION AND OPERATION (Continued)

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