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© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois.

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Presentation on theme: "© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois."— Presentation transcript:

1 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois by Russell Krick

2 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only

3 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only  Anti-lock brake systems (ABS)  Traction and stability control systems  ABS service  Traction and stability control system service  Final system check

4 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only An ABS uses wheel speed sensors, a computer (ECM), and a modulator unit to prevent skidding during hard braking

5 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Anti-Lock Brake System

6 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Operation  For maximum braking and control, extreme tire slip must be avoided  When the tire slips, its friction with the road surface drops, and stopping distance increases  ABS modulates braking effort at the controlled wheels to reduce the stopping distance and increase directional stability when braking

7 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Operation

8 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Basic ABS Components

9 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Components

10 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Wheel Speed Sensors  Produce ac signals that correspond to wheel and tire speed  These signals are fed to the anti-lock brake system control module  As the tire rotates, moving teeth on the sensor rotor induce current in the sensor coil

11 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Wheel Speed Sensor

12 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Sensor Signal Frequency  A rapid decrease in a sensor’s signal frequency indicates that a tire is starting to lose traction and lock up  The control module then sends an electrical signal to the hydraulic modulator to pulsate hydraulic pressure to the affected wheel cylinder, modulating braking effort

13 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Sensor Signal Frequency

14 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Control Module Uses wheel speed sensor inputs to control the electro-hydraulic modulator

15 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only  Regulates the fluid pressure applied to each wheel brake assembly during ABS operation  Controlled by the ABS control module  Pressure modulation refers to the rapid cycling of pressure to the brake assemblies, preventing wheel lockup  occurs 15 to 20 times per second Electro-Hydraulic Modulator

16 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Electro-Hydraulic Modulator

17 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Modulator Components  Fluid reservoir  holds an extra supply of brake fluid  Solenoid valve block  coil-operated valves that control brake fluid flow to the wheel brake cylinders  Accumulator  chamber for storing fluid under high pressure

18 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Modulator Components  Hydraulic pump and motor  motor-driven pump that provides brake fluid pressure for the system  Pressure switch  monitors system pressure and controls the operation of the motor-driven pump  Master cylinder-booster assembly  conventional master cylinder with power assist for normal braking

19 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Hydraulics Here, the brakes are applied, and pressure is being dumped from one wheel to prevent lockup

20 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Circuits

21 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Modes of Operation  Three modes of ABS operation are used:  isolation mode  dump mode  reapply mode

22 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Isolation Mode  The control module detects that a tire is starting to slip  The module energizes a modulator solenoid to isolate that hydraulic circuit from the other brake lines  The fluid is trapped in the wheel brake at the currently applied pressure

23 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Dump Mode  The control module detects that the tire is continuing to slip and slow down  The module energizes a solenoid to release the fluid pressure from the wheel brake assembly to reduce braking effort  The tire speed will tend to increase

24 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Dump Mode

25 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Reapply Mode  The control module detects that the tire speed has increased, so more braking is required  The module de-energizes the dump solenoid and isolation solenoid to allow fluid pressure to build in the brake circuit again, restoring braking effort

26 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Reapply Mode

27 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Warning Light  Mounted in the dash  Used to alert the driver to an ABS malfunction  Turns on during engine cranking and ABS self-check at startup to verify operation

28 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Integrated ABS  Combines the power booster, master cylinder, and modulator units into one assembly  More common on early systems  More expensive and difficult to repair

29 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Nonintegrated ABS  Major units are separated  Uses a conventional master cylinder and booster  The electro-hydraulic modulator is a separate unit  More common on recent ABS units

30 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Channels  Separate hydraulic circuits that feed one or more wheel cylinders or calipers  One-channel ABS  operates only the rear wheel brakes together  Two-channel ABS  two separate hydraulic circuits are controlled by the modulator  rear-wheel ABS with separate control for each wheel brake

31 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Channel  Three-channel ABS  three separate hydraulic circuits are controlled by the modulator  one channel for each front wheel brake  one channel for both rear wheel brakes  Four-channel ABS  four separate hydraulic circuits are controlled by the modulator  provides a separate hydraulic circuit for each wheel brake

32 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Operation (Normal Braking)  Master cylinder pressure flows normally to the brake assembly  No pump or solenoid operation occurs

33 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Operation (Normal Braking)

34 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Operation (Pressure Reduction)  The ABS starts working to avoid a skid  Solenoids close the inlet valve and open the outlet valve  Pressure is released to the reservoir  The caliper pressure is reduced, allowing that wheel to turn

35 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Operation (Pressure Reduction)

36 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Operation (Pressure Increase)  The ABS increases caliper pressure to increase stopping action  Solenoids open the inlet valve and close the outlet valve  High-pressure fluid is sent to the back pressure chamber, and the piston slides to increase pressure to the brake caliper

37 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Operation (Pressure Increase)

38 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Operation (Failure Mode)  The ABS control unit monitors the pressure in the high-pressure passage  When the pressure drops, the control unit turns on the ABS warning light  The sleeve moves and hydraulically locks the back pressure chamber  The master cylinder is connected to the caliper for normal braking

39 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Operation (Failure Mode)

40 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only

41 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Traction Control Systems  Designed to prevent the vehicle’s wheels from spinning and losing traction under hard acceleration  Most systems work with the anti-lock brake system to cycle hydraulic pressure to the wheel spinning the fastest

42 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Traction Control Systems  The control module is capable of applying only one wheel brake at a time  Some systems also reduce the engine’s power output to reduce slipping  The indicator light is illuminated anytime the traction control system is activated  warns the driver that the tires are losing traction

43 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Stability Control Systems  Advanced systems that reduce tire spin upon acceleration and prevent tire skid when cornering too quickly  Use more input signals from various sensors to provide greater control under severe cornering, braking, and acceleration conditions

44 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Understeer  If understeer is detected, the control module will apply braking force to the rear wheel on the opposite side of the vehicle  this brings the front of the vehicle back under control for making the turn

45 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Understeer

46 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Oversteer  If oversteer is detected, the control module will apply braking force to the outside front wheel  this prevents the rear of the vehicle from sliding sideways in a turn

47 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Oversteer

48 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Stability Control System Inputs  Wheel speed sensors  detect individual wheel speeds  Steering angle sensor  measures how sharply the steering wheel is rotated  Lateral acceleration sensor  measures how much side force is generated by a turn

49 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Stability Control System Inputs  Yaw sensor  measures the direction of the thrust generated by vehicle movement  Throttle position sensor  measures the demand for power  Brake pressure sensor  measures the amount of brake system hydraulic pressure generated by the driver

50 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Stability Control System Inputs

51 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only  To service anti-lock brake systems properly, you should be familiar with how a normally operating system feels during operation  You should also be familiar with the exact type of ABS being repaired  Designs and procedures vary  Follow the service manual procedures

52 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Inspection  Inspect for the following conditions:  ABS indicator light on  low or contaminated brake fluid  brake fluid leaks  brake pad lining and rotor wear  tires that will not rotate freely  loose or worn wheel bearings  different tire size or poor tire condition  wheel speed sensor damage

53 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Scanning ABS  Perform a diagnostic circuit check by starting the car and watching the ABS warning light  the lamp should illuminate and then go out after the system self-check is complete  If the ABS light stays on, use a scan tool to check for diagnostic trouble codes

54 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Scanning ABS Typical scan tool connections

55 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Scanning ABS  Connect a scan tool to the data link connector or separate ABS diagnostic connector  Check for a code history and review all trouble codes  When available, perform manual or automatic tests, which will verify system operation  pump, lamp, and solenoid operation

56 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Scanning ABS This tester can be placed on the seat to check operating values during a road test

57 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Pinpoint Tests  Use pinpoint tests to determine the exact source of a problem  Use a multimeter or oscilloscope to check circuit components  Compare the voltage and resistance values to the service manual specifications

58 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Pinpoint Test Chart

59 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Speed Sensor Service  Make sure the sensor is mounted properly  Check that all wire connectors are tight  Check for chipped or broken trigger wheel teeth

60 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Speed Sensor Service If applicable, use a non-metal feeler gauge to check the air gap

61 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Speed Sensor Service  Unplug the sensor connector from the wiring harness  Connect a hand-held scope across the sensor leads  Rotate the tire by hand while watching the sensor waveform

62 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Oscilloscope Connection

63 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Sensor Waveform

64 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Sensor Replacement Replace any clips that retain the wiring

65 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Modulator Check  Some manufacturers support output tests that can verify solenoid and pump operation  These tests may allow the technician to make scan tool selections or jump specified diagnostic connector terminals to activate ABS outputs

66 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Modulator Check  Raise the vehicle on a lift or jack stands  Release the parking brake and rotate each wheel by hand

67 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Modulator Check Connect a jumper wire or make scan tool selections to apply or release the wheel brake assemblies as needed

68 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Modulator Check With the brake applied, rotate each wheel, verifying the ability to apply or vent pressure at each brake assembly

69 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Modulator Replacement

70 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Modulator Replacement Transfer the necessary parts from the old unit to the new one

71 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Bleeding  Nonintegral system  when servicing a master cylinder, bench bleed the unit before installation  install the unit and re-bleed it at the lines  Integral system  the master cylinder requires very specific bleeding procedures  Bleeding may require a scan tool to energize the solenoids and pump motor

72 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Bleeding Special procedures may be required; follow the manufacturer’s instructions

73 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Test-Drive  Use extreme caution  If scan data must be monitored, have a second technician ride along to monitor the data  Where necessary, wet a small strip of pavement about a foot wide and 20 feet long

74 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only ABS Test-Drive  Position the car so the right or left tires ride on wet pavement  Use this area to trigger an anti-lock event while braking  This will allow you to verify ABS operation and to make sure the ABS indicator light stays off

75 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only  The procedures are similar to ABS service  Perform a careful system inspection  Using a scan tool, check for diagnostic trouble codes and check scan data  Use pinpoint tests to isolate any problem  After service, verify the repair

76 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Test-Driving the Vehicle  Similar to an ABS test-drive  Use extreme caution  A wet pavement or a gravel surface lowers friction, allowing you to produce wheel slip on acceleration  Have a second technician ride along to monitor the scan data

77 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only  Before releasing the vehicle, perform some final checks:  clear the diagnostic trouble codes  check the brake fluid level  carefully test-drive the vehicle  simulate a panic stop  make sure the ABS indicator light stays off


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