GMC chevrolet camaro 2000 Service Manual page 726

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Brakes
Antilock Brake System
When wheel slip is noted during a brake application,
the ABS will enter Antilock mode. During Antilock
braking, hydraulic pressure in the individual wheel
circuits is controlled to prevent any wheel from
slipping. If the vehicle is equipped with traction control
a separate hydraulic line and specific solenoid
valves are provided for each wheel. If the vehicle is
not equipped with traction control then both front
wheels have a seperate hydraulic line and specific
solenoid valves, the rear wheels have only
one hydraulic line controlled by one set of solenoid
valves. The ABS can decrease, hold, or increase
hydraulic pressure to each wheel brake. However, it
cannot increase hydraulic pressure above the
amount which is transmitted by the master cylinder
during braking.
During Antilock braking, a series of rapid pulsation's
will be felt in the brake pedal. These pulsation's
are caused by the rapid changes in position of the
individual solenoid valves as they respond to
their desired wheel speed. This pedal pulsation is
present during Antilock braking and will stop when
normal braking is resumed or when the vehicle comes
to a s1op. A ticking or popping noise may also be
heard as the solenoid valves rapidly cycle. During
Antilock braking on dry pavement, the tires maY make
intermittent chirping noises as they approach
slipping. These noises and pedal pulsation's should b.e
considered normal during Antilock operation.
Vehicles equipped with ABS may be stopped by
applying normal force to the brake pedal. Brake pedal
operation during normal braking should be no
different than previous systems. Maintaining a constant
force on the pedal will provide the shortest stopping
distance while maintaining vehicle stability.
Pressure Hold
When the EBCM senses the wheel slip, the EBCM
closes the Inlet valve and keeps the Outlet valve
closed in the BPMV in order to isolate the system. This
holds the pressure steady on the brake so that the
hydraulic pressure does not increase or decrease.
Pressure Decrease
If during the pressure hold mode the EBCM still
senses wheel slip, the EBCM will decrease the
pressure to the brake. The Inlet valve is left closed
and the Outlet valve is opened. The excess fluid
is stored in the accumulator until the return pump can
return the fluid to the master cyclinder.
Pressure Increase
If during the pressure hold or the pressure decrease
mode the EBCM senses that the wheel speed is
too fast, the EBCM will increase the pressure to the
brake. The Inlet is opened and the Outlet valve is
closed. The increased pressure comes from the master
cylinder and is related to the pressure applied to the
brake pedal.
Antilock Brake System 5-253
Traction Control
Traction control will not have any effect on the
operation of the vehicle until the control module
detects one or both of the rear wheels rotating faster
than the front wheels. At this time the Electronic
Brake and .Traction Control Module (EBCM) will
request the Powertrain Control Module (PCM) to retard
timing. If the EBCM continues to detect the rear
wheel are rotating faster than the front it will request
the ASM to reduce the throttle angle. The last measure
taken to control the rear wheel is for the EBCM to
apply the rear brakes, thus reducing torque to the rear
wheels. Once the rear wheels begin to rotate at the
same speed as the front wheels, the system will return
full control to the driver. During Traction Control
mode, if the brake is applied to only one rear wheel,
most of the torque from the engine will be directed
to the other rear wheel which will improve the traction
of the vehicle.
The braking is accomplished by closing the TCS Master
Cylinder Isolating Vaive, this isolates the master
cylinder from the rest of the system. The TCS Prime
valve opens to allow the pump to get brake fluid to build
pressure for braking. The drive wheel circuit solenoids
are energized as needed to allow for pressure hold,
pressure increase, or pressure decrease.
The TCS may be deactivated by the driver if desired.
In order to deactivate the TCS with the engine
running, depress the TCS On/Off switch. The system
will remain deactivated until the ignition switch is
cycled, or the S\{\/itch is pressed again.
Tires"With ABS/TCS
The compact ,spare tire rotates faster than the others.
The EBCM compensates for this faster rotation.
Refer to Tires and Wheels in Suspension for
information on replacement tires.
Replacement Tires
The tire size is important for the performance of the
ABS/TCS. The replacement tires should be the
same size load range and construction as the original
tires. Replace the tires in axle i;>ets and only with
tires of the same tire performance criteria specification
number. Use of any other tire size or type may
seriously affect ABS/TCS operation. For information
on replacement tires for this vehicle, Refer to Tires and
Wheels in Suspension.
BRAKE Warning Indicator
The red BRAKE Indicator in the instrument cluster will
illuminate to warn the driver of conditions in the
brake system which may result in reduced braking
ability. The red BRAKE indicator will also illuminate
when the park brake is .applied. The BRAKE warning
Indicator will stay illuminated until the condition
has been repaired, or the park brake is released. Refer
to Brake System Testing in Hydraulic Brakes.