Volvo VHD Automobile User Manual


 
236 Brakes
Antilock Braking System (ABS)
The vehicle has a standard brake system,
equipped with an electronic speed monitor-
ing and control system, Antilock Braking
System (ABS). ABS monitors wheel speed
continuously but is not involved in control-
ling the wheel speed unless there is an
emergency. In normal braking applications,
the standard air brake system is in effect.
WARNING
For proper ABS operation, do not
change tire sizes. The size of the tires
installed during production are pro-
grammed into the electronic control unit.
Installing different sized tires could re-
sult in a reduced brake force, leading to
longer stopping distances or accidents.
There is a sensor installed in each wheel on
a monitored axle. The sensors transmit in-
formation to the electronic control unit
(ECU). The ECU interprets the signals and
calculates wheel speed, wheel retardation
and a vehicle reference speed. If the calcu-
lations indicate a wheel lock-up situation, a
signal is sent from the ECU to the appropri-
ate ABS modulator valve to reduce braking
pressure. During emergency braking, the
modulator valve alternately reduces, in-
creases or maintains air pressure in the
brake chamber to prevent wheel lock-up.