ANTI-LOCK BRAKING SYSTEMS
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ANTI-LOCK BRAKING SYSTEMS
QUESTIONS FREQUENTLY ASKED ABOUT
ANTI-LOCK BRAKES...
GM offers Anti-lock Brake Systems as standard or optional on all
North American passenger vehicles and light truck lines. The com-
puterized Anti-Lock Braking System (ABS) is designed to keep the
vehicle’s wheels rotating as the brakes are applied to assist the driver
in achieving a controlled stop. Sensors monitor how fast the wheels
rotate and feed the data continuously to the ABS computer. The vehi-
cle’s brakes slow each wheel as the brake pedal is applied. However,
when ABS is activated due to road conditions, the system repeatedly
releases and applies pressure to the brakes. The wheels can keep
rolling, thus retaining steering ability and enhanced stability while
providing a higher braking force on most surfaces than a locked
wheel provides.
How exactly does ABS work?
In cars without
ABS, hitting the brakes can cause the wheels to lock,
leaving you unable to steer the vehicle until you decrease the pressure
so the wheels can roll again. With an ABS, as you apply the brakes, the
ABS computer monitors the wheel speed sensor information. If the
computer senses that a wheel is approaching lock up, it sends a signal
to the hydraulic modulator to reduce, then to reapply, brake pressure
several times a second for as long as you maintain firm pressure on
the brake pedal. The process is much like the threshold braking tech-
nique used with conventional brakes. However, ABS does it much faster
and more accurately than any driver can, leaving you free to focus
on steering away from obstacles.
Does ABS reduce stopping distances?
Yes, in braking situations where the wheels on a non-ABS equipped
vehicle would lock up, ABS will generally provide shorter controlled
stopping distance. The amount of improvement in stopping distance
depends on many factors, including the road surface, severity of
braking, initial vehicle speed, etc. On some surfaces, such
as gravel roads, braking distances can be longer, but you will still have
the control benefits of
ABS.
The important ca
pability of
ABS is control.
ABS provides improved vehicle steerability and stability when braking.
What can affect the ABS advantage?
It is important that you follow the maintenance schedule recommend-
ed in the owner’s manual of the vehicle, tires should be at their proper
inflation level, the brake pads should be checked regularly, etc. While
driving, you should sit comfortably, so that your hips are back in the
seat and your knees are bent, even while braking. Your foot should
be positioned so that your heel is on the floor and your toes are
secure on the lower half of the pedal. And, though ABS may reduce
stopping distance, remember: The faster you go, the longer it takes
you to stop. Keeping a safe distance between you and the vehicle in
front of you is always
necessary, even with ABS.
What happens if ABS becomes inactive?
The ABS electronic control unit has on-board diagnostic capability. If
a fault is detected, the vehicle will revert to the base brake system, and
the ABS telltale on the dash will be illuminated. Should this happen,
the vehicle should be taken to a dealership for repair as soon as
possible.
How do I use ABS?
Depress and hold the pedal. DO NOT PUMP THE BRAKES (that prevents
the system from working). Just hold the brake pedal down and let the
ABS work for you. You may feel the brake pedal vibrate, or you may
notice some noise, but this is normal as the system works for you.
Should I drive an ABS equipped vehicle differently than
I would drive a vehicle with conventional brakes?
Most of the time, under normal driving circumstances, there is no
difference, and you should always drive with the same caution and
care. It is important to realize that ABS only makes a difference when
it is activated—when you have to brake hard—and that would only be
when the computer senses that a wheel is approaching lock up. When
ABS
activates keep steady pressure on the brake pedal and then let the
ABS work for you. Don’t pump the brakes or try to find the threshold.
Simply hold the brake pedal do
wn and steer if necessary to avoid an
obstacle.
Is ABS always active?
ABS is always available, but not always activated. ABS is activated only
when the brake pedal is a
pplied and the computer detects an
impending wheel lock condition.
