Ford 2002 F650 Owner's Manual page 114

Driving
If the red BRAKE warning lamp in
the instrument cluster remains BRAKE
illuminated after engine start up,
!
this indicates a system failure in the
master cylinder of the brake system.
Stop the vehicle safely as soon as possible and seek service immediately.
If the yellow BRAKE RESERVE
BRAKE
(E-motor) warning light remains on
while the engine is running, this
indicates inadequate hydraulic
booster pressure or reserve pump
system failure. Stop the vehicle safely as soon as possible and seek
service immediately.
Four-wheel anti-lock brake system (ABS) (if equipped)
On vehicles equipped with an anti-lock braking system (ABS), a noise
from the hydraulic pump motor and pulsation in the pedal may be
observed during ABS braking events. Pedal pulsation coupled with noise
while braking under panic conditions or on loose gravel, bumps, wet or
snowy roads is normal and indicates proper functioning of the vehicle's
anti-lock brake system. If the vehicle has continuous vibration or shudder
in the steering wheel while braking, the vehicle should be inspected by a
qualified service technician.
The ABS operates by detecting the
onset of wheel lockup during brake
applications and compensating for
this tendency. The wheels are
prevented from locking even when
the brakes are firmly applied. The
accompanying illustration depicts
the advantage of an ABS equipped
vehicle (on bottom) to a non-ABS
equipped vehicle (on top) during hard braking with loss of front braking
traction.
ABS warning lamp
The warning lamp in the instrument cluster momentarily illuminates
ABS
when the ignition is turned on and the engine is off. If the light does not
illuminate momentarily at start up, remains on after the vehicle reaches
10 to 15 km/h (5 to 10 mph), or continues to flash, the ABS needs to be
serviced.
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