Chrysler 300M, Dodge Interpid. Manual — part 45

HCU (HYDRAULIC CONTROL
UNIT)

DESCRIPTION

The hydraulic control unit (HCU) is mounted to

the CAB as part of the ICU (Fig. 12). The ICU is
located in front of the driver’s side front tire, behind
the inner fender splash shield. The HCU controls 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.

The HCU on a vehicle equipped with traction con-

trol has a valve block that is approximately one inch
longer than a HCU on a vehicle that is equipped
with ABS only in order to incorporate the additional
valves.

For more information, refer to the ICU. (Refer to 5

- BRAKES/HYDRAULIC/MECHANICAL/ICU (INTE-
GRATED CONTROL UNIT) - DESCRIPTION)

OPERATION

The operation of the HCU’s hydraulic circuits can

be found in Hydraulic Circuits And Valve Operation.
(Refer to 5 - BRAKES - ABS/HYDRAULIC/ME-
CHANICAL - OPERATION)

The following topics explain how the different com-

ponents within the HCU operate.

VALVES AND SOLENOIDS

The valve block contains four inlet valves and four

outlet 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.

For information on the valves used with the trac-

tion control system, (Refer to 5 - BRAKES - ABS -
TRACTION CONTROL - OPERATION).

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 5 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.

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. 12). 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, one piston
draws fluid from the accumulators, and the opposing
piston pumps fluid to the master cylinder circuits.
When the antilock stop is complete, the pump/motor
drains the accumulators.

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.

REMOVAL - HCU

To remove the HCU, the ICU must be removed

from the vehicle and disassembled. (Refer to 5 -
BRAKES

-

ABS/HYDRAULIC/MECHANICAL/ICU

(INTEGRATED CONTROL UNIT) - REMOVAL)

INSTALLATION - HCU

To install the HCU, it must be attached to the

CAB, forming the ICU. (Refer to 5 - BRAKES - ABS/
HYDRAULIC/MECHANICAL/ICU

(INTEGRATED

CONTROL UNIT) - ASSEMBLY)

LH

BRAKES - ANTILOCK BRAKE SYSTEM

5 - 75

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. 12). The ICU is located in front of the driver’s
side front tire (Fig. 13), behind the inner fender
splash shield.

Two different ICU’s (HCU and CAB) are used on

this vehicle depending on whether or not the vehicle
is equipped with traction control. The HCU on a
vehicle equipped with traction control has a valve
block that is approximately one inch longer than a
HCU on a vehicle that is equipped with ABS only.

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 traction control (ASR) valves, two
hydraulic shuttle valves, valve block, fluid accumula-
tors, a pump, and an electric motor.

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 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)

For information on the ICU’s hydraulic circuits,

refer

to

HYDRAULIC

CIRCUITS

AND

VALVE

OPERATION. (Refer to 5 - BRAKES - ABS/HY-
DRAULIC/MECHANICAL - OPERATION)

Fig. 12 Integrated Control Unit (ICU)

1 - PUMP/MOTOR
2 - HCU
3 - PUMP/MOTOR WIRING CONNECTOR
4 - CAB

Fig. 13 Integrated Control Unit (HCU And CAB)

Location

1 - ENGINE CRADLE
2 - HCU
3 - CONTROLLER ANTILOCK BRAKE (CAB)
4 - BOTTOM OF WINDSHIELD WASHER RESERVOIR
5 - LEFT FRONT TIRE

5 - 76

BRAKES - ANTILOCK BRAKE SYSTEM

LH

REMOVAL - ICU

(1) Remove the remote ground cable from the

ground stud on the right strut tower.

(2) Correctly isolate remote ground cable when ser-

vicing vehicle by installing the ground cable insulator
on the strut tower ground stud as shown in (Fig. 14)
and installing the nut on the stud. This will pre-
vent

accidental

grounding

of

the

remote

ground cable.

(3) Using a brake pedal positioning tool such as

shown in (Fig. 15) depress brake pedal past its first 1
inch of travel and hold in this position. This will iso-
late the master cylinder reservoir from the brake
hydraulic system, not allowing the brake fluid to
drain out of the reservoir.

(4) Remove the bolt and 2 nuts securing the speed

control servo to vehicle. Disconnect the wire harness
connector from speed control servo. Leaving the cable
attached to the speed control servo, move it aside,
out of the way.

(5) Remove the screw attaching the washer bottle

filler neck to the vehicle. Move neck to the side with-
out loosening the filler tube (Fig. 16).

(6) Remove the nut and bolt holding the transmis-

sion controller and bracket to vehicle (Fig. 16). Lift
transmission controller up and move away from
mounting position.

(7) Using Mopar

t Brake Parts Cleaner or an

equivalent, thoroughly clean all surfaces of the HCU.
Also, thoroughly clean all brake tube to HCU connec-
tions.

Fig. 14 Correctly Isolated Remote Ground Cable

1 - CABLE ISOLATOR
2 - GROUND STUD
3 - GROUND CABLE

Fig. 15 Brake Pedal Holding Tool Installed

1 - CLUTCH PEDAL (IF EQUIPPED WITH MANUAL TRANSAXLE)
2 - THROTTLE PEDAL
3 - BRAKE PEDAL HOLDING TOOL
4 - STEERING WHEEL
5 - DRIVER’S SEAT
6 - BRAKE PEDAL

Fig. 16 Transmission Controller Mounting

1 - POWER DISTRIBUTION CENTER
2 - WASHER BOTTLE NECK
3 - TRANSMISSION CONTROLLER MOUNTING BOLT AND NUT

LH

BRAKES - ANTILOCK BRAKE SYSTEM

5 - 77

ICU (INTEGRATED CONTROL UNIT) (Continued)

(8) Remove the primary and secondary brake

tubes coming from the master cylinder, at the HCU,
using a crow foot wrench (Fig. 17).

(9) Remove the chassis brake tubes at the HCU

(Fig. 17), using a crow foot wrench.

CAUTION: Do not apply a 12-volt power source to
any terminals of the 24-way HCU connector when
disconnected from the CAB.

(10) Disconnect the 24-way wiring harness connec-

tor from the CAB using the following procedure.
Grasp the lock on the 24-way connector (Fig. 18), and
pull it up from the connector as far as possible. This
will unlock and raise the 24-way connector out of the
socket on the CAB.

(11) Raise vehicle. (Refer to LUBRICATION &

MAINTENANCE/HOISTING - STANDARD PROCE-
DURE)

(12) Remove the left front tire and wheel assembly.
(13) Remove fasteners securing the inner fender

splash shield in place. Move the splash shield out of
the way.

(14) Remove the 3 bolts attaching the ICU to the

mounting bracket.

(15) Remove the ICU from its mounting bracket.

Then, remove the ICU from the vehicle by pulling it
out around the left side of the mounting bracket,
then through the wheel well.

NOTE: To separate the CAB from the HCU, (Refer to
5 - BRAKES - ABS/HYDRAULIC/MECHANICAL/ICU
(INTEGRATED CONTROL UNIT) - DISASSEMBLY)

DISASSEMBLY - ICU

NOTE: To replace the hydraulic control unit (HCU)
or the controller antilock brake (CAB) on this vehi-
cle, the entire integrated control unit (ICU) needs to
be removed from the vehicle. The CAB can then be
separated from the HCU. Do not attempt to replace
the CAB with the ICU mounted in the vehicle.

(1) Remove the ICU from the vehicle. Refer to

REMOVAL.

(2) Disconnect the pump/motor wiring harness

from the CAB (Fig. 19).

Fig. 17 Brake Tube Fittings

1 - CROW FOOT WRENCH
2 - PRIMARY AND SECONDARY BRAKE TUBES FROM MASTER
CYLINDER
3 - CHASSIS BRAKE TUBES

Fig. 18 24-way CAB Connector Lock

1 - 24–WAY CAB CONNECTOR
2 - CONNECTOR LOCK

Fig. 19 Integrated Control Unit (ICU)

1 - PUMP/MOTOR
2 - HCU
3 - PUMP/MOTOR WIRING CONNECTOR
4 - CAB

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BRAKES - ANTILOCK BRAKE SYSTEM

LH

ICU (INTEGRATED CONTROL UNIT) (Continued)