Automotive Technology
 Chapter
Objectives
• Explain how antilock brake systems work
to bring a vehicle to a controlled stop.
• Describe the differences between an
integrated and a nonintegrated ABS.
• Briefly describe the major components of a
two-wheel antilock brake system.
• 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.
• Explain the best procedure for finding
ABS faults.
• List the precautions that should be
followed whenever working on an ABS.
First introduced on 1954 Lincoln
 1978 Mercedes made first ABS that
worked well
 Can’t defy the law of nature or
physics
 Reduces distance to stop
 Most effective on dry concrete


Antilock Brakes





Normal driving will not notice difference
Anti-lock Event
Unrestricted tire rotation is 0% slip
Tire locked up is 100% slip
When we have 100% slip, the tire loses
traction and vehicle motion changes into
heat energy. (not very effective!)
Maximum Braking Force
Between 10 and 20 Percent Slip
WET CONCRETE


Locked wheels
prevent directional
control
Wheel lock up can
be prevented by
limiting brake
pressure to a point
just short of lockup.
• Pressure Modulation
• Pedal Feel

Diagonally Split System
• Controls Two Hydraulic circuits (2 channel)

Front/Rear Split System
• Controls Three Hydraulic circuit (3 channel)

Full Four Wheel System
• Controls Four Hydraulic Circuits (4 channel)
(page 203) Usually intergrated with traction
control
Page 228C
Normal operation when in conventional
mode (if warning light, disables ABS)
 Heavy braking causes hydraulic pressure
modulation (Pedal Feel)
 Integrated System (Combined parts)227C
 Non-Integrated System (Separate Parts)
 ABS operates independently of base
system

ABS Operation/Modes Description - Page 226C - 227C
ELECTRONIC CONTROL
UNIT







Inputs and Outputs
(228C)
Some ABS ECU’s
have dual boards
Controls HCU
Full Diagnostics
Controls Warning
Lights
Can control each
wheel brake
independently. (four
channel) Most are
three channel
Mechanical Noises
HYDRAULIC CONTROL UNIT
(HCU)
Teves
Mk IV
Page
261C
Hydraulic Control Unit
(Integral)
Hydraulic Control Unit
(Non-Integral)
ACCUMULATOR
Stores high
pressure brake
fluid from Pump
Supplies high
pressure fluid in
ABS mode
2800 to 3400 PSI
Must bleed before
replacement or
service
257C
PUMP AND MOTOR
Motor is 12V Electric (235C)
 Works independently of the base
brake system
 Pressurizes brake fluid up to 2800
psi.
 Turns on when ever pressure drops
below a predetermined level
 Some are replaceable seperately

WHEEL SPEED SENSORS



Detects rotation of
wheel
Permanent magnet
type
3 Parts
• Permanent magnet
• Coil
• Yoke

Induces AC voltage
varied frequency
229C to 231C
RELUCTOR (Tone Ring)
ELECTRICAL
COMPONENTS

Pg 235C
HCU SOLENOID RELAY
• Used on some systems
HCU MOTOR RELAY
 MAIN POWER RELAY
 PRESSURE SWITCHES (430L)

• Generally will turn on Anti-lock Warning
light
PUMP MOTOR RELAY
B+
Cruise Control
TCC
Switch Operation
Or
Power Relay
Brake Lights
CHMSL
ABS
SELF DIAGNOSTICS



Each time Ignition
is turned on ABS
does a self
diagnostic check.
Some systems do
check while car is
moving.
Indicator Lamp
Operation

ABS
Components
• Hydraulic
Components
– Accumulator
– Valve Block
– Booster pump
– Booster/master cylinder assembly
Accumulator

Other Hydraulic Components
– Fluid accumulators
– Hydraulic control unit
– Main valve
– Modulator unit
– Solenoid valve
– Valve block assembly
– Wheel circuit valves

Electrical/Electronic Components
–
–
–
–
–
–
–
–
–
–
–
ABS control module
Brake pedal sensor
Data link connector (DLC)
Diagnostic trouble code (DTC)
Indicator lights
Lateral acceleration sensor
Pressure switch
Pressure differential switch
Relays
Wheel speed sensor
Toothed ring
• Four-Wheel Systems (Integral)
ABS System – No Braking
• Four-Wheel Systems (Integral)
ABS System – ABS in Operation
•
•
•
•
•
•
•
•
GM ABS-VI
Add on System
Electromagnetic
Fast acting
solenoid valves
Screw Plungers
4 Channel
Can cycle 7 times
per second
5 Separate
Diagnostic modes
• General Motors'
Electromagnetic
Antilock Brake
Systems
• Automatic
Traction
Control
• Integration
with Traction
Control

Automatic Stability Control

Automatic Stability Control

Automatic Stability Control

Antilock Brake System Service
• Safety Precautions
• Relieving Accumulator Pressure

Diagnosis and Testing
•
•
•
•
•
•
Pre-Diagnostic Inspection
Visual Inspection
Test Drive
Self-Diagnosis
Testers and Scanning Tools
Testing Components with ABS Scan Tools
• Testing Components with a Lab Scope
• Testing Components with a Lab Scope
• Component Replacement
– Wheel speed sensor service
– Brake system bleeding