10-04-2017, 07:54 PM
Technician Guidelines for Antilock Braking Systems
[attachment=380]
AN INTRODUCTION TO ANTILOCK BRAKING
This section reviews several basic antilock braking system
(ABS) concepts. When you complete this section, you should be
able to answer the following questions:
What is an ABS?
Why are antilock braking systems (ABSs) standard on
most new commercial vehicles?
How does an ABS work?
What are the major features and benefits of ABSs?
How should I drive an ABS-equipped vehicle during a
road test?
What is an ABS?
Antilock braking systems (ABSs) are electronic systems that
monitor and control wheel slip during vehicle braking. ABSs
can improve vehicle control during braking, and reduce
stopping distances on slippery (split or low coefficient of
friction) road surfaces by limiting wheel slip and minimizing
lockup. Rolling wheels have much more traction than locked
wheels. Reducing wheel slip improves vehicle stability and
control during braking, since stability increases as wheel slip
decreases.
ABS COMPONENT DESCRIPTIONS & OPERATION
This section describes the design and operation of ABS
components.
When you complete this section, you should understand the
purpose and function of all major ABS parts including: the ECU,
the modulator valve, the wheel speed sensor, ABS malfunction/
indicator lamp, ABS diagnostic components, and traction
control.
Modern antilock braking systems all feature the following
major components (See Fig. 1 on page 9 for typical system):
Electronic Control Unit (ECU)
Modulator Valves
Wheel Speed Sensors (pickup and exciter)
ABS Malfunction Indicator Lamps
Diagnostics
ABS Malfunction Indicator Lamps
Vehicles required to have an ABS must have ABS
malfunction indicator lamps. These lamps must be yellow and
light up when the ABS has a malfunction that affects the
generation or transmission of response or control signals in
the ABS.
ABS malfunction indicator lamps are not required to light up
for every type of malfunction. However, they are required to
light up for short periods of time for a bulb check whenever the
ABS starts to receive electrical power. The warning lamps for
trailers and dollies are not required to light up for a bulb check
unless the vehicle is stopped.
All trailers/dollies built on or after March 1, 1998 must
feature an external ABS malfunction indicator lamp as part of
the ABS. All new trailers must be capable of activating an in-cab
trailer warning lamp beginning in March 2001. The
requirement for an external trailer/dolly indicator lamp expires
in March 2009.
[attachment=380]
AN INTRODUCTION TO ANTILOCK BRAKING
This section reviews several basic antilock braking system
(ABS) concepts. When you complete this section, you should be
able to answer the following questions:
What is an ABS?
Why are antilock braking systems (ABSs) standard on
most new commercial vehicles?
How does an ABS work?
What are the major features and benefits of ABSs?
How should I drive an ABS-equipped vehicle during a
road test?
What is an ABS?
Antilock braking systems (ABSs) are electronic systems that
monitor and control wheel slip during vehicle braking. ABSs
can improve vehicle control during braking, and reduce
stopping distances on slippery (split or low coefficient of
friction) road surfaces by limiting wheel slip and minimizing
lockup. Rolling wheels have much more traction than locked
wheels. Reducing wheel slip improves vehicle stability and
control during braking, since stability increases as wheel slip
decreases.
ABS COMPONENT DESCRIPTIONS & OPERATION
This section describes the design and operation of ABS
components.
When you complete this section, you should understand the
purpose and function of all major ABS parts including: the ECU,
the modulator valve, the wheel speed sensor, ABS malfunction/
indicator lamp, ABS diagnostic components, and traction
control.
Modern antilock braking systems all feature the following
major components (See Fig. 1 on page 9 for typical system):
Electronic Control Unit (ECU)
Modulator Valves
Wheel Speed Sensors (pickup and exciter)
ABS Malfunction Indicator Lamps
Diagnostics
ABS Malfunction Indicator Lamps
Vehicles required to have an ABS must have ABS
malfunction indicator lamps. These lamps must be yellow and
light up when the ABS has a malfunction that affects the
generation or transmission of response or control signals in
the ABS.
ABS malfunction indicator lamps are not required to light up
for every type of malfunction. However, they are required to
light up for short periods of time for a bulb check whenever the
ABS starts to receive electrical power. The warning lamps for
trailers and dollies are not required to light up for a bulb check
unless the vehicle is stopped.
All trailers/dollies built on or after March 1, 1998 must
feature an external ABS malfunction indicator lamp as part of
the ABS. All new trailers must be capable of activating an in-cab
trailer warning lamp beginning in March 2001. The
requirement for an external trailer/dolly indicator lamp expires
in March 2009.