2005 CHRYSLER CARAVAN air condition

DISC BRAKE CALIPER -
FRONT
REMOVAL
REMOVAL - FRONT DISC BRAKE CALIPER
(CONTINENTAL TEVES BRAKES)
(1) Depress the brake pedal past its first inch of
travel and hold it in this position using a brake pedal
depressor (holding) tool. This is done to isolate the
master cylinder from the brake hydraulic system dis-
allowing the brake fluid to completely drain out of
the brake fluid reservoir.
(2) Raise the vehicle. (Refer to LUBRICATION &
MAINTENANCE/HOISTING - STANDARD PROCE-
DURE).
(3) Remove front wheel and tire assembly.
(4) Remove the banjo bolt connecting the brake
hose to the brake caliper. There are two washers (one
on each side of the brake hose fitting) that will come
off with the banjo bolt. Discard these washers.
(5) Remove the 2 caliper guide pin bolts.
(6) Remove the brake caliper from the adapter.
REMOVAL - FRONT DISC BRAKE CALIPER
(TRW BRAKES)
(1) Using a brake pedal holding tool, depress the
brake pedal past its first one inch of travel and hold
it in this position. This will isolate the master cylin-
der from the brake hydraulic system and will not
allow the brake fluid to drain out of the master cyl-
inder reservoir when the lines are opened.
(2) Raise the vehicle. Refer to HOISTING in
LUBRICATION AND MAINTENANCE.
(3) Remove the front tire and wheel assembly.
(4) Remove the banjo bolt connecting the brake
hose to the brake caliper (Fig. 31). There are two
washers (one on each side of the flex hose fitting)
that will come off with the banjo bolt. Discard the
washers.
(5) Remove the two brake caliper guide pin bolts
(Fig. 31).
(6) Remove the disc brake caliper from the disc
brake adapter.
DISASSEMBLY
DISASSEMBLY - CALIPER GUIDE PIN
BUSHINGS (CONTINENTAL TEVES BRAKES)
Before disassembling the brake caliper, clean and
inspect it. Refer to CLEANING or INSPECTION in
this section.(1) Using your fingers, collapse one side of the rub-
ber guide pin bushing. Pull the guide pin bushing out
the other side of the brake caliper mounting boss.
(2) Repeat this procedure on the remaining bush-
ing.
DISASSEMBLY - CALIPER PISTON AND SEAL
WARNING: UNDER NO CONDITION SHOULD HIGH
PRESSURE AIR EVER BE USED TO REMOVE A PIS-
TON FROM A CALIPER BORE. PERSONAL INJURY
COULD RESULT FROM SUCH A PRACTICE.
NOTE: Before disassembling the brake caliper,
clean and inspect it. Refer to CLEANING AND
INSPECTION in this section.
NOTE: The safest way to remove the piston from
the caliper bore is to use the hydraulic pressure of
the vehicle's brake system.
(1) Following the removal procedure in DISC
BRAKE SHOES found in this section, remove the
caliper from the brake rotor and hang the assembly
on a wire hook away from rotor and body of the vehi-
cle so brake fluid cannot get on these components.
Remove the brake shoes, and place a small piece of
wood between the piston and caliper fingers.
(2) Carefully depress the brake pedal to hydrauli-
cally push piston out of its bore. Once completed,
apply and hold down the brake pedal to any position
beyond the first inch of pedal travel using a brake
pedal holding tool. This will prevent the fluid in the
Fig. 31 Brake Caliper Mounting (Typical)
1 - BRAKE HOSE
2 - ADAPTER MOUNTING BOLTS
3 - BANJO BOLT
4 - CALIPER GUIDE PIN BOLTS
5 - 24 BRAKES - BASERS

DISC BRAKE CALIPER - REAR
REMOVAL - REAR DISC BRAKE CALIPER
NOTE: Handling of the rotor and caliper, must be
done in such a way as to avoid damage to the rotor
and scratching or nicking of lining on the brake
shoes.
(1) Depress the brake pedal past its first inch of
travel and hold it in this position using a brake pedal
depressor (holding) tool. This is done to isolate the
master cylinder from the brake hydraulic system dis-
allowing the brake fluid to completely drain out of
the brake fluid reservoir.
(2) Raise the vehicle. (Refer to LUBRICATION &
MAINTENANCE/HOISTING - STANDARD PROCE-
DURE)
(3) Remove rear wheel and tire assembly from
vehicle.
(4) Remove the banjo bolt connecting the brake
hose to the brake caliper. There are two washers (one
on each side of the brake hose fitting) that will come
off with the banjo bolt. Discard these washers.
(5) Remove the disc brake caliper to adapter guide
pin bolts (Fig. 36).
(6) Remove rear caliper from adapter using the fol-
lowing procedure. First rotate front of caliper up
from the adapter. Then pull the rear of the caliper
and the outboard brake shoe anti-rattle clip out from
under the rear abutment on the adapter (Fig. 37).
(7) If the brake rotor requires removal, it can now
be removed by first removing the retainer clips fromthe wheel mounting studs, then pulling the rotor
straight off the studs.
DISASSEMBLY - CALIPER PISTON AND SEAL
WARNING: UNDER NO CONDITION SHOULD HIGH
PRESSURE AIR EVER BE USED TO REMOVE A PIS-
TON FROM A CALIPER BORE. PERSONAL INJURY
COULD RESULT FROM SUCH A PRACTICE.
NOTE: Before disassembling the brake caliper,
clean and inspect it. Refer to CLEANING AND
INSPECTION in this section.
NOTE: The safest way to remove the piston from
the caliper bore is to use the hydraulic pressure of
the vehicle's brake system.
(1) Following the removal procedure in DISC
BRAKE SHOES found in this section, remove the
caliper from the brake rotor and hang the assembly
on a wire hook away from rotor and body of the vehi-
cle so brake fluid cannot get on these components.
Remove the brake shoes, and place a small piece of
wood between the piston and caliper fingers.
(2) Carefully depress the brake pedal to hydrauli-
cally push piston out of its bore. Once completed,
apply and hold down the brake pedal to any position
beyond the first inch of pedal travel using a brake
pedal holding tool. This will prevent the fluid in the
master cylinder reservoir from completely draining
out.
Fig. 36 Caliper Guide Pin Bolts
1 - DISC BRAKE CALIPER
2 - ADAPTER
3 - AXLE
4 - GUIDE PIN BOLTS
5 - DRIVESHAFT (AWD MODELS ONLY)
Fig. 37 Removing/Installing Caliper
1 - LIFT THIS END OF CALIPER AWAY FROM ADAPTER FIRST
2 - DISC BRAKE CALIPER
3 - ADAPTER ABUTMENT
4 - OUTBOARD BRAKE SHOE HOLD DOWN CLIP
5 - OUTBOARD BRAKE SHOE
6 - ROTOR
7 - ADAPTER
5 - 28 BRAKES - BASERS

PEDAL TORQUE SHAFT - RHD
REMOVAL
(1) Remove the instrument panel. (Refer to 23 -
BODY/INSTRUMENT PANEL/INSTRUMENT
PANEL ASSEMBLY - REMOVAL)
(2) Remove the HVAC housing. (Refer to 24 -
HEATING & AIR CONDITIONING/DISTRIBUTION/
HVAC HOUSING - REMOVAL)
(3) Remove the retaining clip at the torque shaft
end of the brake pedal-to-torque shaft link. Remove
the link from the torque shaft. Discard the retaining
clip. It is not to be reused. Replace with a new clip
when reassembled.
(4) Locate the booster input rod-to-brake pedal
torque shaft connection and remove the retaining clip
(Fig. 62). Discard the retaining clip. It is not to be
reused. Replace with a new clip when reassembled.
(5) Remove the four (4) brake booster retaining
nuts from inside the passenger compartment (Fig.
63).
(6) Remove the retaining nut from the brake
booster bracket located above the booster in the
engine compartment (Fig. 63).
(7) Remove the power brake booster bracket.
(8) Rotate the pedal torque shaft and remove it out
the left side of the vehicle.
INSTALLATION
(1) Lubricate both ends of the torque shaft with
MS-4517 Lubricant or equivalent and install the
torque shaft from the left side reversing the removal
procedure.(2) Install the brake booster bracket on the left
end of the shaft.
(3) Install the retaining nut for the brake booster
bracket in the engine compartment. Tighten the
mounting nut to a torque of 29 N´m (250 in. lbs.).
(4) Install the four brake booster retaining nuts
inside the passenger compartment. Tighten the
mounting nuts to a torque of 29 N´m (250 in. lbs.).
(5) Using lubriplate, or equivalent, coat the sur-
face of the brake pedal torque shaft pin where it con-
tacts the booster input rod. Also coat the surface of
the brake pedal torque shaft pin where it contacts
the brake pedal link.
CAUTION: When installing the power brake booster
input rod on the brake pedal torque shaft pin, do
not reuse the old retaining clip.
(6) Install booster input rod on brake pedal torque
shaft pin and install a NEW retaining clip (Fig. 62).
CAUTION: When installing the brake pedal link on
the brake pedal torque shaft pin, do not reuse the
old retaining clip.
Fig. 62 POWER BRAKE BOOSTER BRACKET
1 - BOOSTER BRACKET
2 - PEDAL TORQUE SHAFT
3 - RETAINING CLIP
4 - BOOSTER MOUNTING NUTS
Fig. 63 BOOSTER, TORQUE SHAFT AND PEDAL
MOUNTING
1 - PEDAL MOUNTING NUT
2 - BRAKE PEDAL ASSEMBLY
3 - PEDAL MOUNTING NUT
4 - PEDAL TORQUE SHAFT
5 - BOOSTER MOUNTING NUT
6 - BOOSTER BRACKET
7 - POWER BRAKE BOOSTER
8 - BOOSTER BRACKET MOUNTING NUT
5 - 44 BRAKES - BASERS

(7) Connect the brake pedal link to the torque
shaft. Install a NEW retaining clip at the torque
shaft end of the brake pedal-to-torque shaft link.
(8) Install the HVAC housing. (Refer to 24 - HEAT-
ING & AIR CONDITIONING/DISTRIBUTION/HVAC
HOUSING - INSTALLATION)
(9) Install the instrument panel. (Refer to 23 -
BODY/INSTRUMENT PANEL/INSTRUMENT
PANEL ASSEMBLY - INSTALLATION)
CAUTION: Do not reuse the original brake lamp
switch. The switch can only be adjusted once. That
is during initial installation of the switch. If the
switch is not adjusted properly or has been
removed for some service, a new switch must be
installed and adjusted.
(10) Remove and replace the brake lamp switch
with a NEW switch. (Refer to 8 - ELECTRICAL/
LAMPS/LIGHTING - EXTERIOR/BRAKE LAMP
SWITCH - REMOVAL), (Refer to 8 - ELECTRICAL/
LAMPS/LIGHTING - EXTERIOR/BRAKE LAMP
SWITCH - INSTALLATION)
(11) Road test vehicle to ensure proper operation of
the brakes.
POWER BRAKE BOOSTER
DESCRIPTION
The power brake booster mounts on the engine
compartment side of the dash panel. It is connected
to the brake pedal by the input (push) rod (Fig. 64).
The master cylinder is bolted to the front of the
booster. A vacuum line connects the power brake
booster to the intake manifold.
All Left-Hand-Drive (LHD) vehicles use a 270 mm
single diaphragm vacuum power brake booster. All
Right-Hand-Drive (RHD) vehicles use a 225/200 mm
tandem diaphragm vacuum power brake booster.
Vehicles equipped with Disc/Disc brakes use a dif-
ferent power brake booster than vehicles equipped
with Disc/Drum brakes. Differences between the two
are internal. Service is the same for all boosters.
The power brake booster can be identified by the
tag attached to the body of the booster (Fig. 65). This
tag contains the production part number, the date it
was built, and who the manufacturer of the power
brake booster is.
NOTE: The power brake booster assembly is not a
repairable component and must be replaced as a
complete assembly if found to be faulty in any way.
The check valve located on the power brake
booster face is not repairable, but it can be
replaced separately from the power brake booster.The different engine combinations used in this
vehicle require different vacuum hose routings to the
power brake booster. All vacuum hoses must be
routed from the engine to the power brake booster
without kinks or excessively tight bends.
Fig. 64 Power Brake Booster (Typical)
1 - VACUUM CHECK VALVE
2 - POWER BRAKE BOOSTER ASSEMBLY
3 - INPUT ROD
4 - POWER BOOSTER ASSEMBLY TO DASH PANEL MOUNTING
STUDS (4)
5 - MASTER CYLINDER MOUNTING STUDS (2)
6 - OUTPUT ROD
Fig. 65 MASTER CYLINDER AND BOOSTER
1 - POWER BRAKE BOOSTER
2 - BOOSTER IDENTIFICATION LABEL
3 - FLUID LEVEL SWITCH CONNECTOR
4 - PRIMARY BRAKE TUBE NUT
5 - SECONDARY BRAKE TUBE NUT
6 - MASTER CYLINDER
RSBRAKES - BASE5-45
PEDAL TORQUE SHAFT - RHD (Continued)

PROPORTIONING VALVE
DESCRIPTION - PROPORTIONING VALVE
(HEIGHT SENSING)
NOTE: Only vehicles without antilock brakes (ABS)
have a proportioning valve. Vehicles with ABS uti-
lize electronic brake distribution which is controlled
through the ABS integrated control unit.
Vehicles not equipped with ABS use a height sens-
ing proportioning valve. It is mounted to the body of
the vehicle above the rear axle (Fig. 80). It has an
actuator lever that attaches to the rear axle and
moves with the axle to help the valve sense the vehi-
cle height.
CAUTION: The height sensing proportioning valve
is not adjustable. No attempt should be made to
adjust it. It is replaced as a complete assembly.
CAUTION: The use of after-market load leveling or
load capacity increasing devices on this vehicle are
prohibited. Using air shock absorbers or helper
springs on this vehicle will cause the height sens-
ing proportioning valve to inappropriately reduce
the hydraulic pressure to the rear brakes. This inap-
propriate reduction in hydraulic pressure potentially
could result in increased stopping distance of the
vehicle.
OPERATION - PROPORTIONING VALVE
(HEIGHT SENSING)
Vehicles not equipped with ABS use a height sens-
ing proportioning valve.
The height sensing proportioning valve operates
similarly to a standard proportioning valve in the fol-
lowing way. As hydraulic pressure is applied to the
valve, full input hydraulic pressure is supplied to the
rear brakes up to a certain pressure point, called the
split point. Beyond the split point, the proportioning
valve reduces the amount of hydraulic pressure to
the rear brakes according to a given ratio. Thus, on
light brake applications, approximately equal
hydraulic pressure will be transmitted to both the
front and rear brakes. Upon heavier brake applica-
tions, the hydraulic pressure transmitted to the rear
brakes will be lower than the front brakes. This will
prevent premature rear wheel lockup and skid.
Here is how the height sensing proportioning valve
differs from a standard proportioning valve. As the
height of the rear suspension changes, the height
sensing portion of the proportioning valve changes
the split point of the proportioning valve. When the
height of the rear suspension is low, the proportion-
ing valve interprets this as extra load and the split
point of the proportioning valve is raised to a higher
pressure to allow for more rear braking. When the
height of the rear suspension is high, the proportion-
ing valve interprets this as a light load and the split
point of the proportioning valve is lowered to a lower
pressure and rear braking is reduced.
The height sensing proportioning valve regulates
the pressure by sensing the load condition of the
vehicle through the movement of the proportioning
valve actuator lever (Fig. 80). As the position of the
rear axle changes, depending on the load the vehicle
is carrying, the movement is transferred to the pro-
portioning valve. The proportioning valve adjusts the
hydraulic pressure accordingly.
The height sensing proportioning valve allows the
brake system to maintain the optimal front to rear
brake balance regardless of the vehicle load condi-
tion. Under a light load condition, hydraulic pressure
to the rear brakes is minimized. As the rear load con-
dition increases, so does the hydraulic pressure to
the rear brakes.
Fig. 80 HEIGHT SENSING PROPORTIONING VALVE
1 - PROPORTIONING VALVE
2 - ACTUATOR LEVER
3 - AXLE BRACKET
4 - REAR AXLE
RSBRAKES - BASE5-53

DIAGNOSIS AND TESTING - PROPORTIONING
VALVE (HEIGHT SENSING)
CAUTION: The use of aftermarket load leveling or
load capacity increasing devices on this vehicle is
prohibited. Using air shock absorbers or helper
springs on this vehicle will cause the height sens-
ing proportioning valve to inappropriately reduce
the hydraulic pressure to the rear brakes. This inap-
propriate reduction in hydraulic pressure potentially
could result in increased stopping distance of the
vehicle.
When a premature rear wheel skid is obtained on a
brake application, it may be an indication that the
hydraulic pressure to the rear brakes is above the
specified output from the proportioning valve. This
condition indicates a possible malfunction of the
height sensing proportioning valve, which will
require testing to verify that it is properly controlling
the hydraulic pressure allowed to the rear brakes.
Premature rear wheel skid may also be caused by
contaminated front or rear brake linings.
Prior to testing a proportioning valve for function,
check that all tire pressures are correct. Also, ensure
the front and rear brake linings are in satisfactory
condition.It is also necessary to verify that the
brakes shoe assemblies on a vehicle being
tested are either original equipment manufac-
turers (OEM) or original replacement brake
shoe assemblies meeting the OEM lining mate-
rial specification. This vehicles brake system is
not balanced for aftermarket brake shoe assem-
bly lining material.
If both front and rear brakes check OK, proceed
with the following test procedure for the height sens-
ing proportioning valve.
(1) Road test the vehicle to determine which rear
wheel brake is exhibiting premature wheel skid.
(2) Raise vehicle. (Refer to LUBRICATION &
MAINTENANCE/HOISTING - STANDARD PROCE-
DURE)
(3) Remove the chassis brake tube going to the
rear brake in question at the proportioning valve.
Remove the chassis brake tube coming from the junc-
tion block at the proportioning valve (Fig. 81).
(4) Install the appropriate fittings from Pressure
Test Fittings, Special Tool 6833, into the open ports
of the proportioning valve.(5) Install the previously removed brake lines into
the Pressure Test Fittings. Tighten all tube nuts to
17 N´m (145 in. lbs.).
(6) Install a pressure gauge from Gauge Set, Spe-
cial Tool C-4007-A into the open port on each pres-
sure test fitting. Bleed air out of hose from pressure
test fittings to pressure gauges at the pressure
gauges. Then bleed air out of the brake line being
tested at that rear wheel brake bleeder.
NOTE: Actuator rod is a linear spring and is meant
to flex by design. When rod is raised, it will have
some curvature to it.
(7) Remove the screw fastening the proportioning
valve actuator rod bracket to the rear axle. Raise the
actuator lever to the full-upward position and hold it
there.
(8) With the aid of a helper, apply pressure to the
brake pedal until a pressure of 6895 kPa (1000 psi) is
obtained on the proportioning valve inlet gauge.
Then, based on the type of brake system the vehicle
is equipped with and the pressure specification
shown on the following table, compare the pressure
reading on the outlet gauge to the specification. If
outlet pressure at the proportioning valve is not
within specification when required inlet pressure is
obtained, replace the proportioning valve. (Refer to 5
- BRAKES/HYDRAULIC/MECHANICAL/PROPOR-
TIONING VALVE - REMOVAL)
CAUTION: Do not attempt to adjust the height sens-
ing proportioning valve. If found to be defective,
replace the valve.
(9) Remove the pressure test fittings and pressure
gauges from the proportioning valve.
(10) Install the chassis brake lines in the correct
ports of the proportioning valve. Tighten all tube
nuts to 17 N´m (145 in. lbs.).
(11) If necessary, repeat the above steps on the
remaining side of the proportioning valve which con-
trol the other rear wheel brake.
(12) Attach the actuator lever and bracket to the
rear axle.
(13) Bleed rear brakes. (Refer to 5 - BRAKES -
STANDARD PROCEDURE)
(14) Road test vehicle.
5 - 54 BRAKES - BASERS
PROPORTIONING VALVE (Continued)

BRAKES - ABS
TABLE OF CONTENTS
page page
BRAKES - ABS
DESCRIPTION
DESCRIPTION - ANTILOCK BRAKE
SYSTEM............................87
DESCRIPTION - ANTILOCK BRAKE
SYSTEM (EXPORT)....................87
DESCRIPTION - ELECTRONIC VARIABLE
BRAKE PROPORTIONING...............88
DESCRIPTION - TRACTION CONTROL
SYSTEM............................88
OPERATION
OPERATION - ANTILOCK BRAKE SYSTEM . . 88
OPERATION - ELECTRONIC VARIABLE
BRAKE PROPORTIONING...............89
OPERATION - TRACTION CONTROL
SYSTEM............................89
CAUTION.............................90
STANDARD PROCEDURE - ANTILOCK BRAKE
SYSTEM BLEEDING...................90
SPECIFICATIONS
ABS FASTENER TORQUE...............91
TONE WHEEL RUNOUT................91
WHEEL SPEED SENSOR AIR GAP........91
FRONT WHEEL SPEED SENSOR
REMOVAL.............................91
INSTALLATION.........................92
REAR WHEEL SPEED SENSOR - AWD
REMOVAL.............................92INSTALLATION.........................92
REAR WHEEL SPEED SENSOR - FWD
REMOVAL.............................93
INSTALLATION.........................93
TONE WHEEL
INSPECTION - TONE WHEEL..............94
TRACTION CONTROL SWITCH
DIAGNOSIS AND TESTING - TRACTION
CONTROL SWITCH....................94
REMOVAL.............................95
INSTALLATION.........................95
HYDRAULIC/MECHANICAL
OPERATION - HYDRAULIC CIRCUITS AND
VALVES .............................95
HCU (HYDRAULIC CONTROL UNIT)
DESCRIPTION........................100
OPERATION..........................101
ICU (INTEGRATED CONTROL UNIT)
DESCRIPTION........................102
OPERATION..........................102
REMOVAL
REMOVAL - LHD.....................102
REMOVAL - RHD.....................104
DISASSEMBLY - ICU...................105
ASSEMBLY - ICU......................106
INSTALLATION
INSTALLATION - LHD.................106
INSTALLATION - RHD.................107
BRAKES - ABS
DESCRIPTION
DESCRIPTION - ANTILOCK BRAKE SYSTEM
This section covers the physical and operational
descriptions and the on-car service procedures for the
Mark 20e Antilock Brake System and the Mark 20e
Antilock Brake System with traction control.
The purpose of the antilock brake system (ABS) is
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.
DESCRIPTION - ANTILOCK BRAKE SYSTEM
(EXPORT)
Four-wheel disc antilock brakes are standard on all
models. The Mark 20e antilock brake system is used
on all models. Depending on whether the vehicle is a
left-hand drive (LHD) or right-hand drive (RHD)
model, the integrated control unit (ICU) is located in
one of two locations. On LHD models, the ICU is
mounted above the front suspension cradle/cross-
member below the master cylinder. On RHD models,
the ICU is located behind the front suspension cra-
dle/crossmember on the left side of the vehicle.
RSBRAKES - ABS5-87

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.
OPERATION - ELECTRONIC VARIABLE BRAKE
PROPORTIONING
Upon entry into EVBP 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
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 EVBP 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 EVBP will remain functional during many
ABS fault modes. If both the red BRAKE and amber
ABS warning indicators are illuminated, the EVBP
may not be functioning.
OPERATION - TRACTION CONTROL SYSTEM
The traction control module monitors wheel speed.
During acceleration, if the module detects front
(drive) wheel slip and the brakes are not applied, the
module enters traction control mode. Traction control
operation proceeds in the following order:
(1) Close the normally open isolation 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 valves to
maintain minimum wheel slip and maximum trac-
tion.
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.
If the brakes are applied at anytime during a trac-
tion control cycle, the brake lamp switch triggers the
controller to switch off traction control.
HYDRAULIC SHUTTLE VALVES
Two pressure relief hydraulic 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.
TRACTION CONTROL LAMP
The traction control system is enabled at each igni-
tion cycle. It may be turned off by depressing the
Traction Control Off switch button when the ignition
is in the ON position. The traction control function
lamp (TRAC OFF) illuminates immediately upon
depressing the button.
The traction control function lamp illuminates dur-
ing a traction control cycle, displaying TRAC.
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.
RSBRAKES - ABS5-89
BRAKES - ABS (Continued)