Technical information

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Technician Guidelines for Antilock Braking Systems
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braking/stability. Some vehicles also use a traction control
system in conjunction with the ABS. Traction control helps the
ABS improve vehicle traction by minimizing wheel slip on the
drive axle during acceleration. If a wheel on the drive axle starts
to slip, the traction control system automatically brakes the
wheel slightly, transferring engine torque to the wheels with
better traction. If all the drive wheels start to slip, the traction
control system may also reduce engine power.
Traction control systems are referred to by several different
names, depending on the manufacturer. These include:
• Automatic Traction Control (ATC)
• Traction Control (TC)
• Automatic Slip Regulation/Anti-Spin Regulation (ASR)
C. How Should I Drive an ABS-equipped Vehicle During Road Tests?
It is the consensus of brake experts that drivers should
brake an ABS-equipped vehicle just as they would brake a non-
ABS equipped vehicle.
The proper braking technique is to maintain a steady,
modulated brake application. Modulated, in this case, means
applying only the pressure required to achieve the desired
deceleration. Do not slam on the brakes to make speed
corrections or routine stops.
When operating on slippery surfaces, with or without an
ABS, it is strongly recommended that drivers depress the clutch
when braking. Engine braking itself can cause drive wheels to
slip. Usually, any retarder will automatically be disabled when
the ABS is in use.
Much of what is taught about hydraulic ABSs doesn’t apply
to air ABSs. Thus, it’s important to remember the following:
• Brake as if no ABS is present, with a modulated
application as described previously.
• Unless certain that the entire combination vehicle has a
working ABS, don’t stomp on the brakes in a panic
situation—one or more wheels could lock and cause
the vehicle to jackknife. Even then, be careful because
you can still jackknife or lose control if the vehicle is
travelling too fast.
• Do not expect to feel the brake pedal pulsing or hear
strange sounds when the ABS activates on air-braked
vehicles. These vehicles do not transmit pulsing
pressure to the driver’s foot and the driver probably
will not hear the system cycling.
Brake an ABS-equipped
vehicle just as you
would brake a non-ABS
equipped vehicle.
Only apply the pressure
required to achieve the
desired deceleration.