Presentation is loading. Please wait.

Presentation is loading. Please wait.

 Anti-lock brake systems (ABS)  Traction and stability control systems  ABS service  Traction and stability control system service  Final system.

Similar presentations


Presentation on theme: " Anti-lock brake systems (ABS)  Traction and stability control systems  ABS service  Traction and stability control system service  Final system."— Presentation transcript:

1

2  Anti-lock brake systems (ABS)  Traction and stability control systems  ABS service  Traction and stability control system service  Final system check

3 An ABS uses wheel speed sensors, a computer (ECM), and a modulator unit to prevent skidding during hard braking

4 Anti-Lock Brake System

5 ABS Operation  For good drivers to get maximum braking and control, extreme tire slip must be avoided  On slick pavement 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

6 With and Without ABS

7 Without ABS  Without ABS cars tend to slide to the right because of higher tire adhesion on the road

8 With ABS With ABS cars tend to travel further during hard braking

9 Basic ABS Components

10 ABS Components

11 ABS Control Module Uses wheel speed sensor inputs to control the electro-hydraulic modulator

12 Wheel Speed Sensor Wheel sensors produce an ac signal that corresponds to wheel and tire speed Sensor Rotor moving teeth on the sensor rotor induces current in the wheel sensor coil

13 Wheel Speed Sensor/ Sensor Rotor  Wheel sensors produce an ac signal that corresponds to wheel and tire speed  The signal increases in frequency as the tire rotates faster  As the tire rotates, moving teeth on the sensor rotor induce current in the sensor coil

14 Sensor Signal Frequency

15  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

16 Electro-Hydraulic Modulator

17  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

18 ABS Circuit Warning Light

19 ABS Warning Light  Mounted in the dash  Alerts the driver to an ABS malfunction  Turns on during engine cranking and ABS self-check at startup to verify operation

20 ABS Accumulator The accumulator in the ABS system stores high pressure fluid and Caution should be used when servicing!

21 During Hard Braking  When the ABS system is in operation you will feel a pulsing in the brake pedal; this is caused by the solenoid valves cycling pressure on and off. Some ABS systems can cycle up to 15 times per second.

22 ABS Warning Light  Mounted in the dash  Alerts the driver to an ABS malfunction  Turns on during engine cranking and ABS self-check at startup to verify operation

23 A:ABS control module B: booster pump & motor C: wheel speed sensor D: sensor rotor E: rotor

24 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

25 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

26 ABS Hydraulics Here, the brakes are applied, and pressure is being dumped from one wheel to prevent lockup

27 ABS Modes of Operation  Three modes of ABS operation are used:  isolation mode  dump mode  reapply mode

28 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 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 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 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 ABS Operation (Normal Braking)  Master cylinder pressure flows normally to the brake assembly  No pump or solenoid operation occurs  The ABS system is not functioning during normal driving  The ABS system only becomes active during tire slippage

33 Testing a Wheel Sensor Above: Using a hand-held scope and measuring the wheel sensor signal

34

35 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

36 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

37 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

38 Understeer  When a vehicle has a tendency to turn less sharply than is intended  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

39 Understeer

40 Oversteer  When a vehicle has a tendency to turn more sharply than is intended  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

41 Oversteer

42 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 drive  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

43 Stability Control System Inputs

44  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

45 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

46 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

47 Scanning ABS Typical scan tool connections

48 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

49 Scanning ABS This tester can be placed on the seat to check operating values during a road test

50 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

51 Pinpoint Test Chart

52 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

53 Speed Sensor Service If applicable, use a non-metal feeler gauge to check the air gap

54 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

55 Oscilloscope Connection

56 Sensor Waveform

57 Sensor Replacement Replace any clips that retain the wiring

58 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

59 ABS Modulator Check  Raise the vehicle on a lift or jack stands  Release the parking brake and rotate each wheel by hand

60 ABS Modulator Check Connect a jumper wire or make scan tool selections to apply or release the wheel brake assemblies as needed

61 ABS Modulator Check With the brake applied, rotate each wheel, verifying the ability to apply or vent pressure at each brake assembly

62 Modulator Replacement

63 Transfer the necessary parts from the old unit to the new one

64 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

65 ABS Bleeding Special procedures may be required; follow the manufacturer’s instructions

66 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

67 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

68  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

69 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

70  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


Download ppt " Anti-lock brake systems (ABS)  Traction and stability control systems  ABS service  Traction and stability control system service  Final system."

Similar presentations


Ads by Google