Dodge Neon / Neon SRT-4. Manual — part 52
CAUTION: When removing a wheel speed sensor
from the rear disc brake adapter, do not use pliers
on the sensor head. This may damage the sensor
head. If the sensor has seized, use a hammer and a
punch to tap the edge of the sensor head ear, rock-
ing the sensor side-to-side until free.
(5) Remove the bolt attaching the wheel speed sen-
sor to the rear disc brake adapter (Fig. 11), then
carefully remove the sensor head from the rear disc
brake adapter and vehicle.
INSTALLATION
NOTE: Before proceeding with this procedure,
(Refer to 5 - BRAKES - WARNING).
CAUTION: Failure to install speed sensor cables
properly may result in contact with moving parts or
an over extension of cables causing an open cir-
cuit. Be sure that cables are installed, routed, and
clipped properly.
(1) Install the wheel speed sensor head into the
disc brake adapter (Fig. 11).
(2) Install the wheel speed sensor mounting bolt.
Tighten the mounting bolt to a torque of 12 N·m (105
in. lbs.).
(3) Install the wheel speed sensor cable routing
bracket on the rear strut.
(4) Install wheel speed sensor cable into the rout-
ing clips on the rear brake hose and brake tube.
(5) Connect the wheel speed sensor cable connector
into vehicle wiring harness (Fig. 10). Install the clip
attaching the wheel speed sensor cable connector to
vehicle’s body.
(6) Lower the vehicle.
(7) Road test the vehicle to ensure proper opera-
tion of the base brakes and ABS.
TONE WHEEL
DESCRIPTION
The tone wheel is used in conjunction with the
wheel speed sensors. (Refer to 5 - BRAKES - ABS/
ELECTRICAL/FRONT WHEEL SPEED SENSOR -
DESCRIPTION) or (Refer to 5 - BRAKES - ABS/
ELECTRICAL/REAR WHEEL SPEED SENSOR -
DESCRIPTION)
OPERATION
The tone wheel is used in conjunction with the
wheel speed sensors. (Refer to 5 - BRAKES - ABS/
ELECTRICAL/FRONT WHEEL SPEED SENSOR -
OPERATION) or (Refer to 5 - BRAKES - ABS/ELEC-
TRICAL/REAR WHEEL SPEED SENSOR - OPERA-
TION)
INSPECTION
Tone wheels can cause erratic wheel speed sensor
signals. Inspect tone wheels for the following possible
causes:
• missing, chipped, or broken teeth
Fig. 10 Wheel Speed Sensor Connector
1 - FUEL TANK
2 - TENSION STRUT
3 - WHEEL SPEED SENSOR CONNECTOR
4 - LOCKING TAB
5 - CLIP
Fig. 11 Rear Wheel Speed Sensor
1 - RIGHT REAR WHEEL SPEED SENSOR
2 - TENSION STRUT
5 - 90
BRAKES - ABS
PL/SRT-4
REAR WHEEL SPEED SENSOR (Continued)
• contact with the wheel speed sensor
• wheel speed sensor to tone wheel alignment
• wheel speed sensor to tone wheel clearance
• excessive tone wheel runout
• tone wheel loose on its mounting surface
If a front tone wheel is found to need replacement,
the drive shaft must be replaced. No attempt should
be made to replace just the tone wheel. (Refer to 3 -
DIFFERENTIAL & DRIVELINE/HALF SHAFT -
REMOVAL).
If a rear tone wheel is found to need replacement,
the rear hub and bearing must be replaced. No
attempt should be made to replace just the tone
wheel. (Refer to 2 - SUSPENSION/REAR/HUB /
BEARING - REMOVAL).
If wheel speed sensor to tone wheel contact is evi-
dent, determine the cause and correct it before
replacing the wheel speed sensor or tone wheel.
Check the gap between the speed sensor head and
the tone wheel to ensure it is within specifications.
For wheel speed sensor air gap specifications, (Refer
to 5 - BRAKES - ABS - SPECIFICATIONS).
Excessive tone wheel runout can cause erratic
wheel speed sensor signals. For tone wheel runout
specifications, (Refer to 5 - BRAKES - ABS - SPECI-
FICATIONS). If tone wheel runout is excessive,
determine if it is caused by a defect in the driveshaft
assembly or hub and bearing. Replace as necessary.
Tone wheels are pressed onto their mounting sur-
faces and should not rotate independently from the
mounting surface. Replace the front driveshaft or
rear hub and bearing as necessary.
HCU - HYDRAULIC CONTROL
UNIT
DESCRIPTION - HYDRAULIC CONTROL UNIT
(HCU)
The hydraulic control unit (HCU) is mounted to
the CAB as part of the ICU (Fig. 14). 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.
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. 14). 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 5 - BRAKES/ELECTRI-
CAL/TRACTION CONTROL SWITCH - DESCRIP-
TION).
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.
OPERATION - HYDRAULIC CIRCUITS AND
VALVES
The hydraulic fluid control valves control the flow
of pressurized brake fluid to the wheel brakes during
PL/SRT-4
BRAKES - ABS
5 - 91
TONE WHEEL (Continued)
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 AND
SOLENOID VALVE FUNCTION
The hydraulic diagram (Fig. 12) shows the vehicle
in the normal braking mode of the base brake
hydraulic system. 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.
ABS HYDRAULIC CIRCUIT AND SOLENOID VALVE
FUNCTION
The hydraulic diagram (Fig. 13) 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.
• The normally open and normally closed valves
modulate (build/decay) the brake hydraulic pressure
as required.
• The pump/motor is switched on so that the
brake fluid from the low pressure accumulators is
returned to the master cylinder circuits.
• The brake fluid is routed to either the master
cylinder or the wheel brake depending on the posi-
tion of the normally open valve.
Fig. 12 Normal Braking Hydraulic Circuit
1 - OUTLET VALVE
2 - PUMP PISTON
3 - PUMP MOTOR (OFF)
4 - LOW PRESSURE ACCUMULATOR
5 - NORMALLY CLOSED VALVE (OFF)
6 - TO RIGHT FRONT WHEEL
7 - NORMALLY OPEN VALVE (OFF)
8 - MASTER CYLINDER PRESSURE
9 - FROM MASTER CYLINDER
10 - NOISE DAMPER CHAMBER
5 - 92
BRAKES - ABS
PL/SRT-4
HCU - HYDRAULIC CONTROL UNIT (Continued)
ICU - INTEGRATED CONTROL
UNIT
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. 14). The ICU is located on the driver’s side of
the vehicle, below the master cylinder (Fig. 15).
The ICU consists of the following components: the
CAB, eight (build/decay) solenoid valves (four inlet
valves and four outlet valves), valve block, fluid accu-
mulators, 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 of the HCU or CAB.
For additional information on the CAB, (Refer to 8
-
ELECTRICAL/ELECTRONIC
CONTROL
MOD-
ULES/CONTROLLER
ANTILOCK
BRAKE
-
DESCRIPTION). For additional information on the
HCU, (Refer to 5 - BRAKES - ABS/HYDRAULIC/ME-
CHANICAL/HCU (HYDRAULIC CONTROL UNIT) -
DESCRIPTION).
OPERATION
For information of the ICU, refer to these individ-
ual components of the ICU:
• CONTROLLER ANTILOCK BRAKE (CAB)
(Refer to 8 - ELECTRICAL/ELECTRONIC CON-
TROL
MODULES/CONTROLLER
ANTILOCK
BRAKE - OPERATION)
• HYDRAULIC CONTROL UNIT (HCU) (Refer to
5 - BRAKES - ABS/HYDRAULIC/MECHANICAL/
HCU (HYDRAULIC CONTROL UNIT) - OPERA-
TION)
Fig. 13 ABS Mode Hydraulic Circuit (Without Traction Control)
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
8 - NORMALLY OPEN VALVE (MODULATING)
9 - FROM MASTER CYLINDER
10 - MASTER CYLINDER PRESSURE
11 - CONTROLLED WHEEL PRESSURE
12 - PUMP INTERSTAGE PRESSURE
13 - NOISE DAMPER CHAMBER
PL/SRT-4
BRAKES - ABS
5 - 93
HCU - HYDRAULIC CONTROL UNIT (Continued)
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