Chrysler PT Cruiser 2001 Service Manual Supplement page 1959

GENERAL INFORMATION
tem pressure is further split into four control chan-
nels. During and ABS operation, all wheels are
controlled independently and are on four separate
control channels.
During an antilock stop, "wheel lock-up" does not
necessarily mean that the wheel has locked, it
means only that the wheel is turning slower than
the vehicle speed. This is called "wheel slip" and is
indicated as a percentage. 0% slip means that the
wheel is rolling free and 100% slip means that the
wheel is locked. The antilock system maintains an
average of approximately 20% wheel slip.
It is important to remember that the antilock
brake system does not shorten the vehicle stopping
distance under all driving conditions, but provides
improved control of the vehicle while stopping.
Vehicle stopping distance is still dependent on ve-
hicle speed, weight, tires, road surface, and other
factors.
3.1.2 TRACTION CONTROL SYSTEM (TCS)
DESCRIPTION
The Traction Control System is available on this
vehicle only with ABS. The main purpose of traction
control is to reduce wheel slip and maintain traction
at the driven wheels when road surfaces are wet or
snow covered. The traction control system reduces
wheel slip by braking the wheel that is losing
traction. The system is designed to operate at
speeds below 56 km/h (35 mph).
The control module monitors wheel speed. If
during acceleration the module detects front (drive)
wheel slip and the brakes are not applied, the
control module will enter traction control mode.
Traction control works in the following order when
drive wheel slip is detected.
1. Close the (normally open) isolation valves.
2. Start pump/motor and supply volume/pressure
to front hydraulic circuits (pump runs continu-
ously during traction control).
3. Open and close build and decay valves to main-
tain minimum wheel slip and maximum trac-
tion.
The cycling of the build and decay valves works
similar to ABS except that they work to control
wheel spin by applying brakes. ABS function is to
control wheel skid by releasing brakes.
Two pressure relief valves allow pressure/volume
to return to the reservoir when not consumed by the
build/decay cycles. These are required because the
pump supplies more volume than the system re-
quires.
If at any time the brakes are applied during a
traction control cycle, the brake switch will trigger
the control module to switch off the traction control.
The traction control system will be enabled at
each ignition cycle. It may be turned off by depress-
ing the traction control switch. The traction control
system function lamp will illuminate ''TRAC OFF''
immediately upon depressing the traction control
switch button. The lamp above the odometer will
display ''TRAC'' during a traction control cycle. If
the controller calculates that the brake tempera-
tures are high, the traction control system will
become inoperative until a time-out period has
elapsed. When in this thermal protection mode, the
traction control ''TRAC OFF'' lamp will illuminate;
however, a fault will not be registered.
3.1.3 PEDAL FEEL/VEHICLES
CHARACTERISTICS
There are several pedal feel/vehicle characteris-
tics that are considered normal for antilock braking
that may require further explanation.
When stopping conditions activate the antilock
brakes, the driver may feel some vibrations/
pulsations in the brake pedal and may hear the
electric solenoid valves clicking and the pump mo-
tor running. The vibrations/pulsations are caused
by the isolating, building and decaying of brake
fluid pressure within the brake lines. The ABS
system prevents complete wheel lock-up, but some
wheel slip is required for the best braking perfor-
mance. This slip may result in some tire chirping,
depending on the road surface. The chirping sound
should not be interpreted as total wheel lock-up,
which leaves black tire marks on dry pavement;
antilock braking may leave some light marks.
At the end of an ABS stop, the ABS may function
all the way down to near 0 km/h (0 mph). There may
be a slight brake pedal drop anytime the ABS is
deactivated.
In case of braking on a bumpy surface, the ABS
system may detect wheel locking tendencies due to
wheel hop and cycle ABS. In the scenario the brake
pedal may pulsate with a perceived loss of declara-
tion. ABS braking may also be activated at times
while on dry pavement with sand, gravel, or other
loose debris on the road.
It should be noted that the pulsating pedal feel
characteristic will not illuminate the brake warning
lamps or set a trouble code that is stored in the
Controller Antilock Brake (CAB). When investigat-
ing a hard pedal feel, inspect the sensor and tone
wheel teeth for chips/broken teeth, damaged sensor
pole tips, excessive runout of the tone wheel, or
excessive gap.
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