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 (ABS) on tractors are de-
signed 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:
•
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 Electronic Braking
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
without the sensor information but at a reduced per-
formance level.
If a serious malfunction causes a total loss of one or
more electronic braking circuits, a pure pneumatic
backup system is available.
The following functions can be deactivated in the
event of a malfunction:
•
ABS can be deactivated at one individual
wheel, at one axle, or for the whole vehicle.
•
ATC control can be deactivated. If it is shut
down, then both the ATC brake control and the
ATC engine control will be shut down.
•
If electrical control is lost, the affected axle is
braked by means of the pneumatic redundancy
pressure. The driver must compensate by ex-
erting more force on the brake pedal to stop
the vehicle.
This system has built-in diagnostics to ensure that all
components are operating properly. Under normal
conditions, the system performs a three second self-
check when the ignition is turned on. The two warn-
ing lamps (EBS, ABS) and the information lamp
(ATC) should illuminate for three seconds and then
go out if all EBS components are working properly. If
all three lamps do not switch on or if all three lamps
Steering and Brake Systems
6.5
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