Chrysler RG Voyager. Manual — part 670
(2) Disconnect traction control switch harness from
column harness (Fig. 5).
(3) Using
an
ohmmeter,
check
for
continuity
between pins 1 and 2. With the switch actuated,
there should be continuity between the two pins.
With the switch off, there should be no continuity.
REMOVAL
The traction control switch is located in the upper
shroud. (Refer to 19 - STEERING/COLUMN/UPPER
SHROUD - REMOVAL)
INSTALLATION
The traction control switch is located in the upper
shroud. (Refer to 19 - STEERING/COLUMN/UPPER
SHROUD - INSTALLATION)
HYDRAULIC CONTROL UNIT
(HCU)
DESCRIPTION
DESCRIPTION - MK20e
On vehicles equipped with the MK20e ABS, the
hydraulic control unit (HCU) is mounted to the CAB
as part of the ICU (Fig. 6). 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.
DESCRIPTION - MK25E
On Later Launch production vehicles (which are
equipped with the MK25e ABS), the hydraulic control
unit (HCU) is mounted to the ABM as part of the
ICU (Fig. 7). The HCU controls the flow of brake
fluid to the brakes using a series of valves and accu-
mulators. A pump/motor is mounted on the HCU to
supply build pressure to the brakes during an ABS
stop.
OPERATION
OPERATION - HYDRAULIC CIRCUITS AND
VALVES - MK20e
NOTE: The following applies for Mark 20e ABS only.
The hydraulic fluid control 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.
Fig. 6 Integrated Control Unit (ICU)
1 - PUMP/MOTOR
2 - HCU
3 - PUMP/MOTOR CONNECTOR
4 - CAB
Fig. 7 Integrated Control Unit
1 - ANTILOCK BRAKE MODULE (ABM)
2 - HYDRAULIC CONTROL UNIT (HCU)
3 - PUMP/MOTOR
RS
BRAKES - ABS
5 - 93
TRACTION CONTROL SWITCH (Continued)
NORMAL BRAKING HYDRAULIC CIRCUIT AND
SOLENOID VALVE FUNCTION
The hydraulic diagram (Fig. 8) 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 which builds pres-
sure in the brake hydraulic system to engage the
brakes and stop the vehicle.
Fig. 8 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 - 94
BRAKES - ABS
RS
HYDRAULIC CONTROL UNIT (HCU) (Continued)
ABS PRIMARY HYDRAULIC CIRCUIT AND
SOLENOID VALVE FUNCTION (ABS WITHOUT
TRACTION CONTROL)
The hydraulic diagram (Fig. 9) 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. 9 ABS Without Traction Control - Primary 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
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
RS
BRAKES - ABS
5 - 95
HYDRAULIC CONTROL UNIT (HCU) (Continued)
ABS SECONDARY HYDRAULIC CIRCUIT AND
SOLENOID VALVE FUNCTION (ABS WITHOUT
TRACTION CONTROL)
The hydraulic diagram (Fig. 10) 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 will then be routed to either the
master cylinder or the wheel brake depending on the
position of the normally open valve.
• In the secondary circuit, 1.2 cc brake fluid is
taken in by the lip seal saver to protect the lip seals
on the master cylinder piston.
Fig. 10 ABS Without Traction Control - Secondary Hydraulic Circuit
1 - OUTLET VALVE
2 - PUMP PISTON
3 - LOW PRESSURE ACCUMULATOR PRESSURE
4 - TO RIGHT FRONT WHEEL
5 - FROM MASTER CYLINDER
6 - MASTER CYLINDER PRESSURE
7 - CONTROLLED WHEEL PRESSURE
8 - PUMP INTERSTAGE PRESSURE
9 - LIP SEAL SAVER (SECONDARY CIRCUIT ONLY)
5 - 96
BRAKES - ABS
RS
HYDRAULIC CONTROL UNIT (HCU) (Continued)
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