Vehicles with electronic engines and ABS may have
ATC. On these vehicles, the ATC system automati-
cally limits wheel spin during reduced-traction situa-
tions.
If the vehicle has ATC, there will be a momentary
contact rocker switch on the dash labeled ATC.
When the ATC system is in the NORMAL mode, it
will apply gentle braking to the spinning wheel, to
feed power to the wheel(s) with better traction. If
both wheels are spinning, the system will signal the
electronic engine to reduce power.
Pressing the switch will temporarily allow more drive
wheel spin, to help burn through a thin layer of ice,
or to help throw off accumulated mud or snow. SPIN
mode is indicated by a flashing WHEEL SPIN light.
Pressing the switch again will cycle the system 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
modulator valve on the left-front axle form a control
circuit with the sensor and modulator 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, modulator valve, wiring connection, short
circuit, etc.), the tractor warning light (TRACTOR
ABS) comes on and the control circuit where the fail-
ure occurred is switched to normal braking action.
The remaining control circuit will retain the ABS ef-
fect. Even if the ABS system is completely inopera-
tive, normal braking ability is maintained. An excep-
tion would be if a modulator valve (or combination
modulator valve) is damaged 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 (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.
Brake Systems
12.4
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