1. Antilock Brake, Traction Control, and Stability Control Systems49
Antilock Brake, Traction Control, and Stability Control Systems
Prepared by
Martin Restoule
Algonquin College
Chapter 49

2. Objectives
Explain how antilock brake systems work to bring a vehicle to a controlled stop.
Describe the differences between an integrated and a non-integrated antilock brake system.
Briefly describe the major components of a two-wheel antilock brake system.
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3. Objectives
Briefly describe the major components of a four-wheel antilock brake system.
Describe the operation of the major components of an antilock brake system.
Describe the operation of the major components of automatic traction and stability control systems.
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4. Objectives Explain the best procedure for finding ABS faults.
List the precautions that should be followed whenever working on an antilock brake system.
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5. ABS Features
The ABS system pulses the brakes more rapidly than the driver can (up to 15 times per second).
Pulsing the brakes prevents wheel lockup.
Preventing wheel lockup provides for more stable stopping.
Preventing wheel slip allows the wheels to turn as directed.
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6. A Common ABS System
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7. Hydraulic Components Control valve assembly Booster pump
Controls the release and application of brake system pressure to the wheel brake assemblies.
Booster pump
Provides pressurized hydraulic fluid for the ABS system.
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8. Hydraulic Components Booster/master cylinder assembly
Contains the valves and pistons used to modulate hydraulic pressure during ABS operation.
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9. Hydraulic Components Fluid accumulator
Stores fluid that is removed from the wheel circuits during the ABS cycle.
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10. Hydraulic Components Hydraulic control unit Hydraulic valves
Contains several components in one unit.
Hydraulic valves
Control and direct hydraulic pressure.
Solenoid valves
Main valve
Wheel circuit valves
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11. Electrical/Electronic Components
Control module
Controls ABS operation and monitors the system.
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12. Electrical/Electronic Components
Brake pedal switch
Signals the control module when the brake is applied.
Data Link Connector (DLC)
Provides access to and/or control of vehicle information.
Lateral position sensor
Is used on some systems to monitor sideways movement of the vehicle.
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13. Electrical/Electronic Components
Pressure switch
Controls pump operation and the low pressure warning lamp.
Pressure differential switch
Sends a signal to the control module when there is an undesirable difference of pressure at the wheel brake units.
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14. Electrical/Electronic Components
Wheel speed sensors
Sends wheel speed information to the ABS module.
Is usually comprised of a magnet and a coil of wire and produces an AC signal.
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15. A Typical Four-Wheel ABS System
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16. ABS Types Integral Non-Integral
Combines the master cylinder, power booster, and ABS hydraulic circuitry in one unit.
Non-Integral
Uses a conventional power booster and master cylinder.
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17. ABS System Channels One-channel system Three-channel system
Only modulates both rear brakes at the same time.
Three-channel system
Has individual circuits to each front wheel and one circuit to both rear wheels.
Four-channel system
Controls each wheel separately.
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18. ABS Operating Modes Pressure hold (retaining)
No additional pressure is allowed to reach the brake.
Pressure release (decrease)
Pressure is released so the wheel can turn.
Pressure apply (increase)
Brake pressure is reapplied to the affected brake.
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19. A Typical Traction Control System
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20. A Typical Traction Control System
The technology and hardware of antilock braking systems is used to control tire traction and vehicle stability.
Automatic traction control (ATC) system uses the ABS pump to apply the brakes when a drive wheel attempts to spin and lose traction.
The system works best when only 1 drive wheel has good traction.
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21. Typical Stability Control System
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22. Stability Control System Operation
Like traction control systems, stability controls are based on and linked to the antilock brake system.
On some vehicles the stability control system is also linked to the electronic suspension system.
Stability control systems momentarily apply the brakes at any 1 wheel to correct oversteer or understeer.
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23. Desired Effects of Stability Control
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24. Service Safety Precautions
Always use lines and hoses designed for ABS vehicles.
Never use silicone brake fluid in an ABS system (Dot 3 is usually recommended).
Always follow the proper bleeding procedure.
Never open a bleeder screw with the system pressurized.
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25. Service Safety Precautions
Never disconnect or reconnect electrical connectors with the ignition switch on.
Do not install electronic accessories near any control module.
Keep the wheel speed sensors clean and follow the recommended installation and adjustment procedures.
Never use a hammer to install speed sensor toothed rings.
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26. Diagnostic Tests Pre-diagnostic inspections and test drive
Warning light symptom troubleshooting
On-board ABS control module (trouble code) testing
Individual trouble code and component testing
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27. Visual Inspections Check fluid level.
Inspect hoses, lines, and fitting for leaks or damage.
Inspect all brake components.
Check for loose wheel bearings.
Check outer CV joint alignment.
Check tire tread depth.
Check electrical connections for corrosion and damage.
Inspect wheel sensors and wiring.
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28. Typical Wheel Speed Sensor Waveform
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29. Summary
DOT 3 is recommended for most antilock brake systems and some power brake systems.
Modern antilock brake systems provide electronic/hydraulic pumping of the brakes up to 15 times per second.
ABS systems are classified as integral and non-integral.
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30. Summary
Integrated antilock brake systems combine the master cylinder, hydraulic booster, and hydraulic circuitry in a single assembly.
On a non-integrated ABS, the master cylinder and hydraulic valve unit are separate assemblies, and a vacuum boost is used.
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31. Summary
Automatic traction control (ATC) is a system that applies the brakes or cuts back engine power when a drive wheel attempts to spin and lose traction.
Automatic stability systems correct oversteer and understeer by applying one wheel brake.
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32. Summary
A malfunction in the ABS system typically causes the electronic control module to shut off or inhibit the system.
A loss of hydraulic fluid or power booster pressure will disable the antilock brake system.
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