freightliner WALK-IN VAN CHASSIS Operator's Manual page 59

is switched to the ON position. Once the vehicle
moves faster than about 4 mph (6 km/h), the warning
light goes out only if all of the vehicle's ABS compo-
nents are working properly.
If during vehicle operation, the safety circuit senses a
failure in any part of the ABS system (a sensor,
brake pressure modulator, wiring connection, short
circuit, etc.), the warning light (ABS) comes on and
the control circuit where the failure occurred is
switched to normal braking action. Even if the ABS
system is partially or completely inoperative, normal
braking ability is maintained. An exception would be
if the brake pressure modulator or hydraulic fluid line
is damaged. Since these components are an integral
part of the hydraulic brake system, normal braking
may be impaired or inoperative.
IMPORTANT: If the ABS warning light does not
work as described above or comes on while
driving, repair the ABS system immediately to
ensure full antilock braking capability.
See the diagnostic menu screens in
follow the steps to read the fault codes in the instru-
ment panel diagnostic menu.
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.
WARNING
Although the ABS system improves vehicle con-
trol during emergency braking situations, the
driver still has the responsibility to change driv-
ing styles depending on existing traffic and road
conditions. Failure to change driving styles to
accomodate existing traffic and road conditions
could cause an accident, possibly resulting in
personal injury or death, or property damage.
Air Brake System
General Information
A dual air brake system consists of two independent
air brake systems that use a single set of brake con-
trols. Each system has its own reservoir, plumbing,
and brake chambers. The primary system operates
Hydraulic and Air Brake Systems
the service brakes on the rear axle; the secondary
system operates the service brakes on the front axle.
Do not operate the vehicle with the front brakes
backed off or disconnected. Backing off or dis-
connecting the front brakes will not improve ve-
hicle handling and may lead to loss of vehicle
control resulting in property damage or personal
injury.
Before driving your vehicle, allow time for the air
compressor to build up a minimum of 95 psi (655
kPa) pressure in both the primary and the secondary
systems. Monitor the air pressure system by observ-
ing the dual system air pressure gauges and the low
air-pressure warning light and buzzer. The warning
light and buzzer shut off when the pressure in both
systems reaches 65 to 73 psi (448 to 503 kPa).
The warning light and buzzer comes on if air pres-
sure drops below 65 to 73 psi (448 to 503 kPa) in
Chapter 2, and
either system. If this happens, check the air system
pressure gauges to determine which system has low
air pressure. Although the vehicle's speed can be
reduced using the foot brake control pedal, either the
front or the rear service brakes will not be operating,
causing a longer stopping distance. Bring the vehicle
to a safe stop and have the air system repaired be-
fore continuing.
The parking brake will apply when air pressure drops
below 38 to 42 psi (262 to 290 kPa). Do not wait for
the brake to apply automatically; when the warning
light and buzzer first come on, immediately bring the
vehicle to a safe stop. Before continuing operation of
the vehicle, correct the cause of the air loss.
Air Brake System With External Fill
(Shrader) Valve
If your engine will not start and it is desirable to re-
lease the parking brake, do the following: Block the
wheels. Turn the ignition switch to the ON position.
Fill the air reservoir for the braking system by exter-
nal means. The parking brake will not release until
air pressure reaches 65 psi (448 kPa). The low air
buzzer will sound until air pressure reaches 65 psi
(448 kPa) with the ignition switch in the ON position.
IMPORTANT: If the air pressure in the braking
system drops back below 38 to 42 psi (262 to
290 kPa) the parking brake will reengage.
WARNING
7.2