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Chrysler PT Cruiser. Manual - part 433

wheel speed sensor mounting bosses; loose wheel
speed sensor mounting bolts; excessive tone wheel
runout; excessively large tone wheel-to-wheel speed
sensor air gap, or a damaged speed sensor head face.
Give special attention to these components when
diagnosing

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 the
master 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 -
MK20E

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.

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.

The traction control function indicator illuminates

during 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 indicator (TRAC OFF) illuminates immedi-
ately upon depressing the button. Pressing this but-
ton again or turning off and restarting the vehicle
will enable the traction control system.

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
“thermo-protection mode,” the traction control func-
tion indicator illuminates TRAC OFF; note that no
trouble code is registered.

OPERATION - TRACTION CONTROL SYSTEM -
MK25E

The ABM monitors wheel speed. During accelera-

tion, if the ABM detects front (drive) wheel slip and
the brakes are not applied, the ABM 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.

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.

5 - 84

BRAKES - ABS

BRAKES - ABS (Continued)

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.

The traction control function indicator illuminates

during a traction control cycle, displaying TRAC on
the instrument panel.

The traction control system is enabled at each igni-

If the ABM calculates that the brake temperatures

CAUTION

The ABS uses an electronic control module. This

module is designed to withstand normal current
draws associated with vehicle operation. Care must
be taken to avoid overloading the circuits.

CAUTION: In testing for open or short circuits, do
not ground or apply voltage to any of the circuits
unless instructed to do so for a diagnostic proce-
dure.

CAUTION: These circuits should only be tested
using a high impedance multi-meter or the desig-
nated scan tool as described in this section. Power
should never be removed or applied to any control
module with the ignition in the ON position. Before
removing or connecting battery cables, fuses, or
connectors, always turn the ignition to the OFF
position.

CAUTION: The CAB (MK20e) 25-way connector
should never be connected or disconnected with
the ignition switch in the ON position.

CAUTION: The ABM (MK25e) 47-way connector
should never be connected or disconnected with
the ignition switch in the ON position.

CAUTION: This vehicle utilizes active wheel speed
sensors. Do not apply voltage to wheel speed sen-
sors at any time.

CAUTION: Use only factory wiring harnesses. Do
not cut or splice wiring to the brake circuits. The
addition of aftermarket electrical equipment (car
phone, radar detector, citizen band radio, trailer
lighting, trailer brakes, etc.) on a vehicle equipped
with antilock brakes may affect the function of the
antilock brake system.

CAUTION: When performing any service procedure
on a vehicle equipped with ABS, do not apply a
12-volt power source to the ground circuit of the
pump motor in the HCU. Doing this will damage the
pump motor and will require replacement of the
entire HCU.

CAUTION: An attempt to remove or disconnect cer-
tain system components may result in improper
system operation. Only those components with
approved removal and installation procedures in
this manual should be serviced.

CAUTION: If welding work is to be performed on the
vehicle using an electric arc welder, the CAB
(MK20e) or ABM (MK25e) connector should be dis-
connected during the welding operation.

CAUTION: Many components of the ABS System
are not serviceable and must be replaced as an
assembly. Do not disassemble any component
which is not designed to be serviced.

CAUTION: Only the recommended jacking or hoist-
ing positions for this vehicle are to be used when-
ever it is necessary to lift a vehicle. Failure to raise
a vehicle from the recommended locations could
result in lifting a vehicle by the hydraulic control
unit mounting bracket. Lifting a vehicle by the
hydraulic control unit mounting bracket will result
in damage to the mounting bracket and the hydrau-
lic control unit.

CAUTION: Brake fluid will damage painted surfaces.
If brake fluid is spilled on any painted surface,
wash off with water immediately.

DIAGNOSIS AND TESTING - INSPECTION AND
ROAD TEST

(1) Visually inspect the ABS for damaged or dis-

connected components and connectors.

(2) Verify the brake lamps are operational. If they

are not, repair them prior to continuing.

BRAKES - ABS

5 - 85

BRAKES - ABS (Continued)

(3) Connect a scan tool to the Data Link Connector

located under the instrument panel to the left of the
steering column (Fig. 2). If the scan tool does not
power-up, check the power and ground supplies to
the connector.

(4) Turn the ignition key to the ON position. Using

the scan tool, select ANTILOCK BRAKES.

(5) Read and record any Diagnostic Trouble Codes

(DTCs). If any DTCs are present, refer to the appro-
priate chassis diagnostic information.

NOTE: Diagnostic trouble codes (DTCs) are kept in
the controller’s memory until either erased by the
technician using the scan tool, or erased automati-
cally after 3500 miles or 255 ignition key cycles,
whichever occurs first. DTCs are retained by the
controller even if the ignition is turned off or the
battery is disconnected. More than one DTC can be
stored at a time. When accessed, the number of
occurrences and the DTC that is stored are dis-
played.

If no problems are observed, it will be necessary to

road test the vehicle.

Many ABS conditions judged to be a problem by

the driver may be normal operating conditions. To
become familiarized with the normal operating char-
acteristics of this antilock brake system, (Refer to 5 -
BRAKES - ABS OPERATION).

WARNING: CONDITIONS THAT RESULT IN TURNING
ON THE RED BRAKE WARNING INDICATOR LAMP
MAY INDICATE REDUCED BRAKING ABILITY.

Before road testing a brake complaint vehicle, note

whether the red BRAKE warning indicator lamp,
amber ABS warning indicator lamp, or both are
turned on. If it is the red BRAKE warning indicator,
there is a brake hydraulic problem that must be cor-
rected before driving the vehicle (Refer to 5 -
BRAKES - BASE - DIAGNOSIS AND TESTING). If
the red BRAKE warning indicator is illuminated,
there is also a possibility that there is an ABS prob-
lem and the amber ABS warning indicator is not able
to illuminate, so the MIC turns on the red BRAKE
warning indicator by default.

If the amber ABS warning indicator is on, road test

the vehicle as described below. While only the amber
ABS warning indicator is on, the ABS is not func-
tional. The ability to stop the car using the base
brake system should not be affected.

(6) Turn the key to the OFF position and then

back to the ON position. Note whether the amber
ABS warning indicator lamp continues to stay on.

(7) If the amber ABS warning indicator lamp stays

on, shift into gear and drive the car to a speed of
approximately 25 km/h (15 mph) to complete the ABS
Start-Up and Drive-Off Cycles (Refer to 5 - BRAKES
- ABS - OPERATION). If at this time the amber ABS
warning indicator lamp stays on, refer to the Appro-
priate Diagnostic Information.

(8) If the amber ABS warning indicator lamp goes

out at any time, drive the vehicle a short distance.
Accelerate the vehicle to a speed of at least 64 km/h
(40 mph). Bring the vehicle to a complete stop, brak-
ing hard enough to cause the ABS to cycle. Repeat
this action several times. Using the scan tool, read
and record any Diagnostic Trouble Codes (DTCs). If
any DTCs are present, refer to the Appropriate Diag-
nostic Information.

STANDARD PROCEDURE - ANTILOCK BRAKE
SYSTEM BLEEDING

The base brake’s hydraulic system must be bled

anytime air enters the hydraulic system. The ABS
though, particularly the ICU (HCU), should only
need to be bled when the HCU is replaced or
removed from the vehicle. The ABS must always be
bled anytime it is suspected that the HCU has
ingested air. Under most circumstances that require
the bleeding of the brakes hydraulic system, only the
base brake hydraulic system needs to be bled.

When bleeding the ABS system, the following

bleeding sequence must be followed to insure com-
plete and adequate bleeding.

(1) Make sure all hydraulic fluid lines are installed

and properly torqued.

(2) Connect the scan tool to the Data Link Connec-

tor. The connector is located under the lower steering
column cover to the left of the steering column.

Fig. 2 Data Link Connector Location

1 - DATA LINK CONNECTOR (DLC)

5 - 86

BRAKES - ABS

BRAKES - ABS (Continued)

(3) Using the scan tool, check to make sure the

CAB (MK20e) or ABM (Mk25e) does not have any
fault codes stored. If it does, clear them using the
scan tool.

WARNING: WHEN BLEEDING THE BRAKE SYSTEM
WEAR SAFETY GLASSES. A CLEAR BLEED TUBE
MUST BE ATTACHED TO THE BLEEDER SCREWS
AND SUBMERGED IN A CLEAR CONTAINER FILLED
PART WAY WITH CLEAN BRAKE FLUID. DIRECT THE
FLOW OF BRAKE FLUID AWAY FROM YOURSELF
AND THE PAINTED SURFACES OF THE VEHICLE.
BRAKE FLUID AT HIGH PRESSURE MAY COME OUT
OF THE BLEEDER SCREWS WHEN OPENED.

(4) Bleed the base brake system using the stan-

dard pressure or manual bleeding procedure. (Refer
to 5 - BRAKES - BASE - STANDARD PROCEDURE)

(5) Using

the

scan

tool,

select

ANTILOCK

BRAKES,

followed

MISCELLANEOUS,

then

BLEED BRAKES. Follow the instructions displayed.
When the scan tool displays TEST COMPLETED,
disconnect the scan tool and proceed.

(6) Bleed the base brake system a second time.

Check brake fluid level in the reservoir periodically
to prevent emptying, causing air to enter the hydrau-
lic system.

(7) Fill the master cylinder reservoir to the full

level.

(8) Test drive the vehicle to be sure the brakes are

operating correctly and that the brake pedal does not
feel spongy.

SPECIFICATIONS

ABS FASTENER TORQUE

(Refer to 5 - BRAKES - BASE - SPECIFICATIONS

- BRAKE FASTENER TORQUE)

TONE WHEEL RUNOUT

FRONT TONE WHEEL:

Maximum Runout

0.25 mm (0.009 in.)

REAR TONE WHEEL:

Maximum Runout

0.25 mm (0.009 in.)

WHEEL SPEED SENSOR AIR GAP

DESCRIPTION

SPECIFICATION

FRONT SENSOR

0.30 – 1.50 mm

0.012 –0.059 in.

REAR SENSOR

0.50 – 1.25 mm

0.019 – 0.049 in.

FRONT WHEEL SPEED
SENSOR

DESCRIPTION

The antilock brake system uses two-wire wheel

speed sensors, known as active wheel speed sensors.
The sensors use an electronic principle known as
magnetoresistive to help increase performance and
durability. The sensors convert wheel speed into a
small digital signal. A wheel speed sensor is used at
each wheel. The gear (tooth) type tone wheel serves
as the trigger mechanism for each sensor. At each
wheel of the vehicle there is one wheel speed sensor
and one tone wheel.

The front wheel speed sensors are attached to

bosses in the steering knuckles (Fig. 3) (Fig. 4).
There is a heat shield mounted between each sensor
and the knuckle. The tone wheel is an integral part
of the outboard constant velocity joint located in the
front axle shaft.

WSS air gaps are not adjustable. The initial fac-

tory WSS air gap specification can be found in SPEC-
IFICATIONS. Each WSS is serviced individually. The
tone wheels are serviced as part of the drive shaft.

OPERATION

The CAB (MK20e) or ABM (MK25e) sends 12 volts

to power an Integrated Circuit (IC) in the sensor. The
IC supplies a constant 7 mA power supply to the
CAB/ABM. The relationship of the tooth on the tone
wheel to the permanent magnet in the sensor, signals
the IC to enable a second 7 mA power supply. The

Fig. 3 Left Front Wheel Speed Sensor (Heat Shield

Not Shown)

1 - LEFT FRONT WHEEL SPEED SENSOR
2 - TONE WHEEL

BRAKES - ABS

5 - 87

BRAKES - ABS (Continued)

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