freightliner CENTURY CLASS S Driver Manual page 89

Steering and Brake Systems
ice, or to help throw off accumulated mud or snow.
SPIN mode is indicated by a flashing WHEEL SPIN
light. Pressing NORM/SPIN again will cycle the sys-
tem back to normal operation.
®
The Meritor WABCO ABS system combines one
front-axle control channel with one rear axle to form
one control circuit. For example, the sensor and sole-
noid control valve on the left-front axle form a control
circuit with the sensor and solenoid control valve on
the right rear axle. If, during vehicle operation, the
safety circuit senses a failure in any part of the ABS
system (a sensor, solenoid control valve, wiring con-
nection, short circuit, etc.), the tractor warning light
(TRACTOR ABS) comes on and the control circuit
where the failure occurred is switched to normal
braking action. The remaining control circuit will re-
tain the ABS effect. Even if the ABS system is com-
pletely inoperative, normal braking ability is main-
tained. An exception would be if a solenoid control
valve (or combination solenoid control valve) is dam-
aged and inoperative. As these components are an
integral part of the air brake system, normal braking
may be impaired or inoperative.
IMPORTANT: If any of the ABS warning lights
do not work as described above, or come on
while driving, repair the ABS system immedi-
ately to ensure full antilock braking capability.
During emergency or reduced-traction stops, fully
depress the brake pedal until the vehicle comes to a
safe stop; do not pump the brake pedal. With the
brake pedal fully depressed, the ABS system will
control all wheels to provide steering control and a
reduced braking distance.
Although the ABS system improves vehicle control
during emergency braking situations, the driver still
has the responsibility to change driving styles de-
pending on the existing traffic and road conditions.
For example, the ABS system cannot prevent an ac-
cident if the driver is speeding or following too
closely.
Trailer ABS Lamp Operation
Antilock braking systems on tractors are designed to
communicate with trailer ABS systems, if they are
compatible. Compatibility will result in the illumination
of the trailer ABS lamp during vehicle start-up and
fault detection.
The dash-mounted lamp will operate as follows when
a compatible trailer is properly connected to a tractor:
6.5
•
When the ignition key is turned to the ON posi-
tion, the trailer ABS lamp will illuminate mo-
mentarily, then turn off.
•
If the lamp comes on momentarily during ve-
hicle operation, then shuts off, a fault was de-
tected and corrected.
•
If the lamp comes on and stays on during ve-
hicle operation, there is a fault with the trailer
ABS. Repair the trailer ABS system immedi-
ately to ensure full antilock braking capability.
The Trailer ABS lamp will not illuminate unless a
compatible trailer is connected to the tractor.
IMPORTANT: If a compatible trailer is con-
nected, and the lamp is not illuminating momen-
tarily when the ignition key is turned to the ON
position, it is possible that the lamp is burnt out.
®
Meritor WABCO
System (EBS)
®
The Meritor WABCO Electronic Braking System
(EBS) is designed to continuously monitor and coor-
dinate all aspects of service braking.
The EBS pairs an electronic control system with a
pneumatic application system. Key braking data such
as driver brake demand, wheel speed, and vehicle
load is gathered by a network of electronic sensing
devices (including load sensors, and signal generat-
ing tone wheels and sensors located in the wheel
hubs of each sensing axle).
An electronic control unit, the central module, over-
sees the translation of electronic signals into pneu-
matic actuation. During a braking application,
electronic-pneumatic modulators control the brake
pressure of each wheel, as well as at the trailer cou-
pling head. As a result, the same amount of vehicle
deceleration will occur for a given brake pedal travel,
regardless of vehicle load. During emergency stops
(i.e. wheel lockup), the EBS also activates the An-
tilock Braking System (ABS).
The EBS includes a system check for all modulators,
sensors, brake system electric circuits and data lines
and is thereby able to detect malfunctions in the
braking system. When a fault is detected, the central
module will disable the affected part of the EBS.
Under this safe status (i.e. fail-safe) mode, the nonaf-
fected parts will continue to function. For example, in
the case of a sensor malfunction, the system works
Electronic Braking