2000 DODGE NEON Service Repair Manual

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 20±40 kph
(12±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
verify that premature ABS cycling has been cor-
rected.
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
A vehicle equipped with ABS uses a different mas-
ter cylinder than a vehicle that is not equipped with
ABS. Vehicles equipped with ABS use a center port
master cylinder with only two outlet ports (Fig. 1).
The brake tubes from the primary and secondary
outlet ports on the master cylinder go directly to the
integrated control unit (ICU).
The master cylinder mounts to the power brake
booster in the same manner a non-ABS master cylin-
der does.
INTEGRATED CONTROL UNIT (ICU)
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 driver's side of the
vehicle, and is mounted to the left front frame rail
below the master cylinder (Fig. 1).
5 - 66 BRAKESPL
DESCRIPTION AND OPERATION (Continued)

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 traction
control valves, valve block, fluid accumulators, a
pump, and an electric pump/motor.
The replaceable components of the ICU are the
HCU and the CAB. No attempt should be made to
service any components found inside of the HCU or
CAB.
CONTROLLER ANTILOCK BRAKE (CAB)
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 PCI bus.
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 send a message to the mechanical instu-
ment cluster (MIC) instructing it to 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 commands the CAB command coils to actu-
ate. The CAB command coils then open and close the
valves in the HCU that modulate brake fluid pres-
sure in some or all of 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 of vehicle operation.
Fig. 1 Master Cylinder And ICU
1 ± PRIMARY BRAKE TUBE
2 ± MASTER CYLINDER
3 ± SECONDARY BRAKE TUBE
4 ± ABS ICU
Fig. 2 Integrated Control Unit (ICU)
1 ± HCU
2 ± PUMP/MOTOR
3 ± CAB
PLBRAKES 5 - 67
DESCRIPTION AND OPERATION (Continued)

CONTROLLER ANTILOCK BRAKE INPUTS
²wheel speed sensors (four)
²stop lamp switch
²ignition switch
²system relay voltage
²ground
²traction control lamp
²diagnostic communication (PCI)
CONTROLLER ANTILOCK BRAKE OUTPUTS
²amber ABS warning lamp actuation (through
MIC)
²red BRAKE warning lamp actuation (through
MIC)
²traction control lamp actuation (through MIC)
²diagnostic communication. (PCI)
HYDRAULIC CONTROL UNIT (HCU)
The hydraulic control unit (HCU) is mounted to
the CAB as part of the ICU (Fig. 2). The HCU con-
trols the flow of brake fluid to the brakes using a
series of valves and accumulators. A pump/motor is
mounted on the HCU to supply build pressure to the
brakes during an ABS stop.
VALVES AND SOLENOIDS
The valve block contains four inlet valves and four
outlet solenoid valves. The inlet valves are spring-
loaded in the open position and the outlet valves are
spring-loaded in the closed position during normal
braking. The fluid is allowed to flow from the master
cylinder to the wheel brakes.
During an ABS stop, these valves cycle to maintain
the proper slip ratio for each wheel. The inlet valve
closes preventing further pressure increase and the
outlet valve opens to provide a path from the wheel
brake to the HCU accumulators and pump/motor.
This releases (decays) pressure from the wheel brake,
thus releasing the wheel from excessive slippage.
Once the wheel is no longer slipping, the outlet valve
is closed and the inlet valve is opened to reapply
(build) pressure.
There are four other valves in the HCU. These four
remaining valves are used for traction control. Two
traction control (TC) valves, mounted in the HCU
valve block, are normally in the open position and
close only when the traction control is applied. There
are also two shuttle valves which control pressure
return to the master cylinder under ABS and traction
control conditions.
These TC valves are used to isolate the rear (non-
driving) wheels of the vehicle from the hydraulic
pressure that the HCU pump/motor is sending to the
front (driving) wheels when traction control is being
applied. The rear brakes need to be isolated from the
master cylinder when traction control is beingapplied so the rear wheels do not drag. For more
information on the TC and shuttle valves, see TRAC-
TION CONTROL SYSTEM in this section.
BRAKE FLUID ACCUMULATORS
There are two fluid accumulators in the HCU: one
for the primary hydraulic circuit, and one for the sec-
ondary hydraulic circuit. Each hydraulic circuit uses
a 3 cc accumulator.
The fluid accumulators temporarily store brake
fluid that is removed from the wheel brakes during
an ABS cycle. This stored fluid is used by the pump/
motor to provide build pressure for the brake hydrau-
lic system. When the antilock stop is complete, the
accumulators are drained by the pump/motor.
There are two noise dampening chambers in the
HCU on this vehicle equipped with traction control.
PUMP/MOTOR
There are two pump assemblies in the HCU: one
for the primary hydraulic circuit, and one for the sec-
ondary hydraulic circuit. Both pumps are driven by a
common electric motor (Fig. 2). This DC-type motor
is integral to the HCU and is controlled by the CAB.
The pump/motor provides the extra amount of
brake fluid needed during antilock braking. Brake
fluid is released to the accumulators when the outlet
valve is opened during an antilock stop. The pump
mechanism consists of two opposing pistons operated
by an eccentric camshaft. In operation, these pistons
are used to purge fluid from the accumulators back
into the master cylinder circuits. When the antilock
stop is complete, the pump/motor drains the accumu-
lators.
The pump motor is also used to build pressure
when the system goes into traction control mode. For
more information, refer to TRACTION CONTROL
SYSTEM in this section.
The CAB may turn on the pump/motor when an
antilock stop is detected. The pump/motor continues
to run during the antilock stop and is turned off after
the stop is complete. Under some conditions, the
pump/motor runs to drain the accumulators during
the next drive-off.
The pump/motor is not a serviceable item; if it
requires replacement, the HCU must be replaced.
ABS FUSES
The ABS fuse and the ABS pump/motor fuse are
located in the power distribution center (PDC). Refer
to the sticker on the inside of the PDC cover for the
location of these fuses. The PDC is located on the
driver's side of the engine compartment between the
back of the battery and the brake master cylinder.
The CAB fuse can be found in the fuse junction
block under the instrument panel.
5 - 68 BRAKESPL
DESCRIPTION AND OPERATION (Continued)

AMBER ABS WARNING LAMP
The amber ABS warning lamp is located in the
instrument cluster. The purpose of the warning lamp
is discussed in detail below.
When the ignition key is turned to the ON posi-
tion, the amber ABS warning lamp is lit until the
CAB completes its self-tests and turns off the lamp
(approximately 4 seconds). The amber ABS warning
lamp will illuminate when the CAB detects a condi-
tion that results in the shutdown of ABS function.
The CAB sends a message to the mechanical instu-
ment cluster (MIC) instructing it to turn on the
amber ABS warning lamp.
Under most conditions, when the amber ABS warn-
ing lamp is on, only the ABS function of the brake
system is affected; The electronic brake distribution
(EBD), the base brake system and the ability to stop
the vehicle are not affected.
WHEEL SPEED SENSOR (WSS)
At each wheel of the vehicle there is one wheel
speed sensor (WSS) and one tone wheel (Fig. 3) (Fig.
4) (Fig. 5) (Fig. 6). Each front wheel speed sensor is
attached to a boss in the steering knuckle. The front
tone wheel is part of the driveshaft outboard con-
stant velocity joint. The rear wheel speed sensor is
mounted to the rear disc brake adapter. The rear
tone wheel is an integral part of the rear wheel hub
and bearing.
The wheel speed sensor operates on electronic
energy supplied by the CAB and outputs a square
wave signal whose current alternates between two
constant levels. Its frequency is proportional to the
speed of the tone wheel. The output is available as
long as the sensor is powered and its state (high or
low) corresponds to the presence or absence of tone
wheel teeth. The output signal is sent to the CAB. If
a wheel locking tendency is detected by the CAB, it
will then modulate hydraulic pressure via the HCU
to prevent the wheel(s) from locking.
Correct ABS operation is dependent on accurate
wheel speed signals. The vehicle's tires and wheels
all must be the same size and type to generate accu-
rate signals. Variations in tire and wheel size can
produce inaccurate wheel speed signals.
Improper speed sensor-to-tone wheel clearance can
cause erratic speed sensor signals. The speed sensor
air gap is not adjustable, but should be checked when
applicable. Wheel speed sensor-to-tone wheel clear-
ance specifications can be found in the SPECIFICA-
TIONS section within this section in this service
manual group.
ELECTRONIC BRAKE DISTRIBUTION
Vehicles equipped with ABS use electronic brake
distribution (EBD) to balance front-to-rear braking.The EBD is used in place of a rear proportioning
valve. The EBD system uses the ABS system to con-
trol the slip of the rear wheels in partial braking
range. The braking force of the rear wheels is con-
trolled electronically by using the inlet and outlet
valves located in the integrated control unit.
Upon entry into EBD the inlet valve for the rear
brake circuit is switched on so that the fluid supply
from the master cylinder is shut off. In order to
decrease the rear brake pressure, the outlet valve for
Fig. 3 Left Front Wheel Speed Sensor
1 ± LEFT FRONT WHEEL SPEED SENSOR
2 ± TONE WHEEL
Fig. 4 Right Front Wheel Speed Sensor
1 ± RIGHT FRONT WHEEL SPEED SENSOR
2 ± TONE WHEEL
PLBRAKES 5 - 69
DESCRIPTION AND OPERATION (Continued)

the rear brake circuit is pulsed. This allows fluid to
enter the low pressure accumulator (LPA) in the
hydraulic control unit (HCU) resulting in a drop in
fluid pressure to the rear brakes. In order to increase
the rear brake pressure, the outlet valve is switched
off and the inlet valve is pulsed. This increases the
pressure to the rear brakes. This back-and-forth pro-
cess will continue until the required slip difference is
obtained. At the end of EBD braking (brakes
released) the fluid in the LPA drains back to themaster cylinder by switching on the outlet valve and
draining through the inlet valve check valve. At the
same time the inlet valve is switched on in case of
another brake application.
The EBD will remain functional during many ABS
fault modes. If both the red BRAKE, and amber ABS
warning lamps are illuminated, the EBD may not be
functioning.
TRACTION CONTROL SYSTEM
Traction control reduces wheel slip and maintains
traction at the driving wheels at speeds below 56 kph
(35 mph) when road surfaces are slippery. The trac-
tion control system reduces wheel slip by braking the
wheel that is losing traction.
The CAB monitors wheel speed. During accelera-
tion, if the CAB detects front (drive) wheel slip and
the brakes are not applied, the CAB enters traction
control mode. Traction control operation proceeds in
the following order:
(1) Close the normally open traction control (TC)
valves.
(2) Start the pump/motor and supply volume and
pressure to the front (drive) hydraulic circuit. (The
pump/motor runs continuously during traction con-
trol operation.)
(3) Open and close the build and decay solenoid
valves to maintain minimum wheel slip and maxi-
mum traction.
The cycling of the build and decay valves during
traction control is similar to that during antilock
braking, except the valves work to control wheel spin
by applying the brakes, whereas the ABS function is
to control wheel skid by releasing the brakes.
HYDRAULIC SHUTTLE VALVES
Two pressure relief shuttle valves allow pressure
and volume to return to the master cylinder reservoir
when not consumed by the build and decay valves.
These valves are necessary because the pump/motor
supplies more volume than the system requires.
If the brakes are applied at anytime during a trac-
tion control cycle, the brake lamp switch triggers the
control module to switch off traction control.
TRACTION CONTROL FUNCTION LAMP
The traction control function lamp illuminates dur-
ing a traction control cycle, displaying TRAC on the
instrument panel.
The traction control system is enabled at each igni-
tion cycle. It may be turned off by depressing the
traction control switch button. The traction control
function lamp (TRAC OFF) illuminates immediately
upon depressing the button. Pressing this button
again, or turning off and restarting the vehicle will
enable the traction control system.
Fig. 5 Left Rear Wheel Speed Sensor
1 ± LEFT REAR WHEEL SPEED SENSOR
2 ± TENSION STRUT
Fig. 6 Right Rear Wheel Speed Sensor
1 ± RIGHT REAR WHEEL SPEED SENSOR
2 ± TENSION STRUT
5 - 70 BRAKESPL
DESCRIPTION AND OPERATION (Continued)

If the CAB calculates that the brake temperatures
are high, the traction control system becomes inoper-
ative until a time-out period has elapsed. During this
ªthermo-protection mode,º the traction control func-
tion lamp illuminates TRAC OFF; note that no trou-
ble code is registered.
HYDRAULIC CIRCUITS AND VALVE OPERATION
The hydraulic shuttle valves control the flow of
pressurized brake fluid to the wheel brakes during
the different modes of ABS braking. The following
paragraphs explain how this works. For purposes of
explanation only, it is assumed that only the right
front wheel is experiencing antilock braking; the fol-
lowing diagrams show only the right front wheel in
an antilock braking operation.
NORMAL BRAKING HYDRAULIC CIRCUIT,
SOLENOID VALVE, AND SHUTTLE VALVE
FUNCTION (ABS WITH TRACTION CONTROL)
The hydraulic diagram (Fig. 7) shows a vehicle
with traction control in the normal braking mode.
The diagram shows no wheel spin or slip occurring
relative to the speed of the vehicle. The driver is
applying the brake pedal; this builds pressure in the
brake hydraulic system to engage the brakes and
stop the vehicle. The hydraulic shuttle valve closes
with every brake pedal application so pressure is not
created at the inlet to the pump/motor.
Fig. 7 ABS With Traction Control - Normal Braking Hydraulic Circuit
1 ± OUTLET VALVE
2 ± PUMP PISTON
3 ± PUMP MOTOR (OFF)
4 ± SUCTION VALVE
5 ± LOW PRESSURE ACCUMULATOR
6 ± NORMALLY CLOSED VALVE (OFF)
7 ± TO RIGHT FRONT WHEEL8 ± NORMALLY OPEN VALVE (OFF)
9 ± NORMALLY OPEN ASR VALVE (OFF)
10 ± FROM MASTER CYLINDER
11 ± HYDRAULIC SHUTTLE VALVE
12 ± MASTER CYLINDER PRESSURE
13 ± NOISE DAMPER CHAMBER
PLBRAKES 5 - 71
DESCRIPTION AND OPERATION (Continued)

ABS BRAKING HYDRAULIC CIRCUIT, SOLENOID
VALVE, AND SHUTTLE VALVE FUNCTION (ABS
WITH TRACTION CONTROL)
The hydraulic diagram (Fig. 8) shows the vehicle in
the ABS braking mode. The diagram shows one
wheel is slipping because the driver is attempting to
stop the vehicle at a faster rate than is allowed by
the surface on which the tires are riding.
²The hydraulic shuttle valve closes upon brake
application so that the pump/motor cannot siphon
brake fluid from the master cylinder.²The normally open and normally closed valves
modulate (build/decay) the brake hydraulic pressure
as required.
²The pump/motor is switched on so that the
brake fluid from the low pressure accumulators is
returned to the master cylinder circuits.
²The brake fluid is routed to either the master
cylinder or the wheel brake depending on the posi-
tion of the normally open valve.
Fig. 8 ABS With Traction Control - ABS Braking Hydraulic Circuit
1 ± OUTLET VALVE
2 ± PUMP PISTON
3 ± PUMP MOTOR (ON)
4 ± SUCTION VALVE
5 ± LOW PRESSURE ACCUMULATOR
6 ± NORMALLY CLOSED VALVE (MODULATING)
7 ± TO RIGHT FRONT WHEEL
8 ± NORMALLY OPEN VALVE (MODULATING)9 ± NORMALLY OPEN ASR VALVE (OFF)
10 ± FROM MASTER CYLINDER
11 ± HYDRAULIC SHUTTLE VALVE
12 ± MASTER CYLINDER PRESSURE
13 ± CONTROLLED WHEEL PRESSURE
14 ± LOW PRESSURE ACCUMULATOR PRESSURE
15 ± PUMP INTERSTAGE PRESSURE
16 ± NOISE DAMPER CHAMBER
5 - 72 BRAKESPL
DESCRIPTION AND OPERATION (Continued)

ABS TRACTION CONTROL HYDRAULIC CIRCUIT,
SOLENOID VALVE, AND SHUTTLE VALVE
FUNCTION (ABS WITH TRACTION CONTROL)
The hydraulic diagram (Fig. 9) shows the vehicle in
the traction control (TC) mode. The diagram shows a
drive wheel is spinning and brake pressure is
required to reduce its speed.
²The normally open TC (ASR) valve is energized
to isolate the brake fluid being pumped from the
master cylinder and to isolate the driven wheel.
²The normally open TC (ASR) valve bypasses the
pump output back to the master cylinder at a fixed
pressure setting.
²The normally open and normally closed valves
modulate (build/decay) the brake pressure as
required to the spinning wheel.
Fig. 9 Traction Control Hydraulic Circuit
1 ± OUTLET VALVE
2 ± PUMP PISTON
3 ± PUMP MOTOR (ON)
4 ± LOW PRESSURE ACCUMULATOR PRESSURE
5 ± LOW PRESSURE ACCUMULATOR
6 ± NORMALLY CLOSED VALVE (MODULATING)
7 ± TO RIGHT FRONT WHEEL (SPINNING)
8 ± NORMALLY OPEN VALVE (MODULATING)
9 ± NORMALLY OPEN ASR VALVE ON (REGULATING)10 ± FROM MASTER CYLINDER
11 ± HYDRAULIC SHUTTLE VALVE
12 ± CONTROLLED WHEEL PRESSURE
13 ± SUCTION VALVE
14 ± PUMP INTERSTAGE PRESSURE
15 ± NOISE DAMPER CHAMBER
16 ± MASTER CYLINDER PRESSURE
17 ± PUMP PRESSURE
PLBRAKES 5 - 73
DESCRIPTION AND OPERATION (Continued)