ABS (Antilock Braking System) prevents wheel lockup during hard braking to allow steering control. It uses sensors and a computer to monitor wheel speeds and pulse the brakes if a wheel locks up to maintain 20-50% slip. This improves braking performance and helps prevent skids. ABS components include wheel speed sensors, an ECU (computer), and hydraulic control valves that pulse the brakes individually. It can be a two-wheel or four-wheel system and only activates during braking over 15 mph.

1. ABS Braking
Systems
Braking Systems
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2. ABS
 Antilock Brake System or ABS prevents
the wheels from locking during hard
braking
 Improves driver control
 Helps prevent skids from the wheels
locking up and sliding
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3. ABS Stopping
 ABS braking is used to help shorten the
stopping distance of a vehicle
 Stopping distance is affected by:
 Vehicle speed
 Type and tread depth of tires
 Driver use of the brakes
 Road conditions – dry, rainy, ice, gravel
 Front, 4, or rear wheel drive
 Engine location – front, mid, rear
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4. ABS
 ABS is based on braking while
maintaining control of the vehicle
 When brakes lock, the driver cannot
steer or control the vehicle, as the wheels
are no longer turning
 Traction loss is called 100% slip
 ABS maintains 20-50% slip – providing
control and better braking
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5. ABS Function
 ABS uses sensors and a computer to
monitor the speed the wheels are turning
 If a wheel locks up (100% slip) the
computer pulsates the brakes of that
wheel to allow it to still turn and be in
control
 ABS pulsations allow the driver to
maintain control and steer the vehicle
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6. ABS
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7. ABS Pedal Feel
 ABS brakes have “pedal feedback”
 The brake pedal will feel and function
normally during normal braking
 When ABS braking is activated, the pedal
will pulsate quickly
 Once ABS braking is completed, pedal
feel will return to normal
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8. ABS Components
 Common ABS components on all
systems:
 ECU – computer control unit for ABS
 Wheel speed sensors – read the speed of
each wheel to input to ECU – magnetic
 Hydraulic control valve assembly – pulsates
the ABS and brake hydraulic pressures to
pulse ABS
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9. ABS components
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10. ABS ECU
 The computer that controls the ABS
system
 Wheel speed sensors act as inputs to tell
ECU when to activate ABS
 Controls the hydraulic control assembly
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11. ABS ECU
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12. ECU
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13. Wheel speed sensor
 Wheel speed sensors detect the rotation speed
of the vehicle’s wheels
 Consist of a sensor (usually magnetic) and a
tone ring
 ABS may have 3 or 4 sensors – 1 in each front
wheel and 1 or 2 for the rear wheels
 Send the signal to the ECU to determine speed
and lock up (slip) percentage to pulse the ABS
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14. Wheel speed sensor
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15. Wheel speed sensor
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16. Wheel speed sensors
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17. Hydraulic Control Valves
 Controls the ABS pulses and lock up for
each wheel individually
 Contains solenoids that open and close,
allowing brake fluid to be sent to and
returned from the wheels as ABS pulses
 Only functions when ABS is engaged
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18. Hydraulic control valves
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19. Hydraulic control valve
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20. Types of ABS systems
 Integral ABS – early systems
 Non-integral ABS – used on most current
vehicles
 Two wheel ABS – only controls 2 wheels
 Four wheel ABS – controls all 4 wheels
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21. Integral ABS
 Used on early cars, until the 90’s
 Master cylinder, brake booster and ABS
controller were all one large unit
 Used pumps to control brake and ABS
pressure
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22. Non-integral ABS
 Used on most modern vehicles
 Uses “normal” brake master and booster
 Separate, replaceable ABS unit in line
with master
 Does not use a pump
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23. Two wheel ABS
 Only controls the ABS on the rear wheels
 Also called single channel ABS
 Used for trucks and SUVs
 Prevents the rear from sliding and
causing vehicle to spin out
 Only 1 wheel speed sensor
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24. Four wheel ABS
 Controls front and rear wheels
 Can have 3 or 4 speed sensors – 1 for
each front wheel, and 1 or 2 for the rear
 3 channel has 3 sensors
 4 channel has 4 – one at each wheel –
safer and more accurate
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25. How ABS works
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26. How ABS works
 ABS only works at speeds above 15mph
 If the ABS system fails, it will simply turn
off, and “non ABS” braking will still
function normally – a warning light will
come on in the dash to alert of failure
 You will feel the ABS pulse through the
brake pedal when in use
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27. ABS light
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28. ABS service
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29. ABS service
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