ABS - Antilock Braking System

[seminar class]

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ANTI-LOCK BRAKES
ABS, (Anti-Lock brake system)
 ABS allows the driver to maintain steering control of the vehicle while in hard braking situations .
ANTI-LOCK BRAKES
 Computerized ABS is designed to keep the wheels from locking as the brakes are applied.
 A locked wheel provides very little or no directional control.
 The following slides show the common ABS components.
 Some components are part of both the conventional and ABS system.
 When operating a vehicle with ABS never pump the brakes.
 Doing so will make the ABS system ineffective.
Always apply firm pressure.
 Drivers may experience a pulsation in the brake pedal, or pedal kick back during an ABS stop. This is normal and not to be confused with a conventional brake pedal pulsation
 Major components of the anti-lock brake system consist of a
• Brake control module,
• Solenoid valve assembly,
• Speed sensor's
• Wiring, and the amber ABS brake warning light.
Brake Control Module:
 The brake control module is a compute that receives information from the speed sensor and compares it to the speed of other wheels.
 When one wheel is approaching lock-up pressure can be vented allowing the wheel nearing lock-up to speed up.
 If a wheel is to fast pressure can be increased to slow down the wheel.
 If both wheel are approximately the same speed the brake control module can enter a pressure hold mode of operation.
Solenoid Valve Assembly:
Is a pair of valves that can:
A. Increase pressure
B. Hold pressure steady
C. Decrease pressure
 ABS system can maintain extremely high static pressure and must be disabled before attempting repairs.
 Normally pumping brake 20-30 times will release pressure.
 ABS brake system are
• Integrated
• Nonintegrated
 An integrated system has the master cylinder and control valve assembly made together.
 A nonintegrated has the master cylinder and control valve assembly made separate.
 ABS operates using the same hydraulic principal as conventional brakes.
 ABS system only operates when wheel lock-up is emanate.
 A bussing noise and bakes pedal vibration is normal during ABS operation.
 To determine if wheel lock-up is about to occur vehicles a wheel speed sensor.
 There 3 ABS configurations
• 1. channel normally RWAL (rear wheel anti-lock)
• In a one channel RWAL system the rear wheels are controlled together
• ANTI-LOCK BRAKES
 ABS brakes are either
• 1. Channel
• 3 Channel
• 4 Channel
 1 channel ABS system controls the rear wheel together.
 A 1 channel system only has 1 speed sensor and control valve assembly.
 A three (3) channel ABS system control the rear wheel together and the front independently.
 Three channel ABS system have 3 speed sensor and one (1) control module
 Wheel Slippage, is the wheel speed in relation to vehicle speed.
 If vehicle speed is faster than the wheel speed slippage is negative. And the wheel may become lock-up
 If vehicle speed is slower than wheel speed. Wheel slippage is positive.
 Positive wheel slippage occurs when a wheel is spinning.
 NOTE: Late model vehicles use the same ABS components with traction control. Traction control prevent a vehicle from spinning out of control.
 The best braking action occurs at between 10-20%.
 If vehicle speed and wheel speed is the same wheel slippage is 0%
 A lock-up wheel will have a wheel slippage of 100%
 In a diagonally split system brake system the left front and right rear brakes are controlled together.
 Diagonally split systems offer an added safety value.
 When diagnosing an ABS concern always
• 1. Talk with customer/ owner, to deterring if the ABS at fault or a basic brake system concern
• 2. Always check the basic brake system 1st.
• 3. Check for proper tire size
• 4. Check for damage sensor and reluctor rings.
• 5. Check brake light operation
• 6. Check for diagnostic trouble codes
ABS QUIZ
 1. Technician A says, That ABS works only in a panic situation. Technician B says ABS works when wheel lock-up is determine. Who is correct?
• A. Technician A only B. Technician B only
• C. Neither A nor B D. Both A and B
 2. Technician A says a lock-up wheel provides no directional control. Technician B says a lock-up wheel provides a shorter stopping distance. Who is correct?
 A. Technician A only B. Technician B only
 C. Both A and B D. Neither A nor B
 3. What component is used to determine vehicle speed?
• A. Throttle position sensor
• B. Mass air flow meter
• C. Oxygen sensor
• D. Wheel speed sensor
 4. Technician A says when operating a vehicle with ABS brakes you should pump the brake. Technician B says to hold firm when applying brakes. Who is correct?
 A. Technician A only B. Technician B only
 C. Both A and B D. Neither A nor B
 ABS QUIZ
 5. What type brake fluid should never be used with an ABS system?
• A. DOT 3
• B. DOT 4
• C. DOT 5
• D. All the above can be used