Brakes (Abs) - Saab 9001994 Owner's Manual

74 Car care and technical information
Brake system including
ABS
The standard anti-lock braking system on
the Saab 900 is a triple circuit system, with
split circuits and individual monitoring and
control for each front wheel and for the two
rear wheels together.
Signals from the four wheel sensors are
sent to the ABS control module, which com-
putes at a given instant the wheel speed,
acceleration and deceleration, the road
speed and tire slip. If a wheel is about to
lock, the control module will send signals to
the solenoid valves for the wheel con-
cerned, whereupon the pressure in the
brake circuit for the wheel will be modulated
to ensure that the optimum braking effect,
and thus the maximum coefficient of adhe-
sion, is achieved.
In addition to the electronically controlled
features of the Saab Anti-lock Brake Sys-
tem, two other functions set it apart from
conventional brake systems:
• A triple split-circuit system with individual
circuits for the left front wheel, the right
front wheel and the two rear wheels to-
gether.
• The brake servo unit is hydraulically op-
erated instead of being operated by the
vacuum in the inlet manifold.
The brakes are power assisted but it should
be remembered that the servo unit oper-
ates only when the ignition is on. Much
greater pressure will need to be applied to
the brake pedal to apply the brakes when
the engine is switched off, e.g. if the car is
being towed, or if a failure occurs in the hy-
draulic pump.
Three brake warning lights are incorporated
into the instrument cluster. A light comes on
when the hand brake is applied, one comes
on to indicate a failure in the ABS and one
indicates a loss of brake fluid (or a drop in
the servo pressure in the ABS unit).
WARNING!
1 If the BRAKE FLUID and ANTI LOCK
warning lights are illuminated at the
same time, the car must not be driven.
After several pedal applications, the
brake pedal effort will increase unex-
pectedly and the braking effect will be
greatly reduced. Note, however, that
the operation of the handbrake will be
unaffected. Failure to heed this warning
may result in inadequate braking and
possibly personal injury.
2 The ANTI LOCK warning light will illu-
minate when a fault occurs in the anti-
lock braking system. When the ANTI
LOCK warning light illuminates and the
BRAKE FLUID warning light does not,
the anti-lock braking system will deac-
tivate and the vehicle will revert to a
standard braking system without the
benefit of the anti-lock features. The car
should be checked and corrected im-
mediately by an authorized Saab
dealer.
NOTE
If the brake pedal continues to move
down under constant pressure or the car
pulls to one side during braking or an ab-
normally loud or metallic noise is heard
during braking see an authorized Saab
dealer immediately to have the braking
system inspected.