Troubleshooting guide

36
www.bendix.com 1-800-AIR-BRAKE (1-800-247-2725)
ABS Components continued ...
• Dash-mounted tractor ABS Indicator Lamp
• Service brake relay valve
• Dash-mounted trailer ABS Indicator Lamp (used on
all towing vehicles manufactured after March 1,
2001)
• Optional blink code activation switch
• Optional ABS off-road switch. (Off-road feature is
not typically available on all models)
Some “Premium” Bendix ABS systems utilize additional
components, such as traction control valves, a dash-
mounted ATC status/indicator lamp, serial
communication to the engine control module, a stop
lamp switch input, and optional ATC off-road switch.
With advanced ABS, the roll stability and ESP features
require additional components including vehicle sensors
to detect vehicle motion (lateral and yaw-rate sensors,
and pressure sensors for load estimation) and driver
intention (by monitoring the turning of the steering
wheel).
All Bendix ECUs feature digital electronics with self
test and diagnostic circuitry that continuously monitors
operation of the entire antilock system including wiring
continuity. A history of all diagnostic trouble codes
are stored in the controller's memory and are not
cleared by loss of power to the unit.
ECU controllers are typically available in frame-
mounted and cab-mounted models.
Truck and Tractor ABS Operation
As described in the introduction to this section, Bendix
ABS uses wheel speed sensors, modulator valves, and
an ECU. By monitoring individual wheel turning motion
during braking, the ECU is able to optimize slip between
the tire and the road surface by pumping the brakes on
individual wheels (or pairs of wheels), independently.
Steer Axle Control
Although both wheels of the steer axle have their own
wheel speed sensor and pressure modulator valve, the
ECU blends the applied braking force between the two
steering axle brakes. A Bendix patented brake
application control, called Modified Individual Regulation
(MIR), has been designed to help reduce steering wheel
pull during an ABS event on road surfaces with poor
traction (or areas of poor traction, e.g. asphalt road
surfaces with patches of ice).
Vehicle Configurations
Depending on the number of drive axles, various
numbers of sensors and modulators may be used for
an ABS system. For example, a 4 sensor/4 modulator
(4S/4M) system would typically be used for a single drive
axle vehicle. System configurations are available for
4S/4M, 6S/6M, and 6S/5M (with the additional axle, a
non-driven rear axle, having two sensors, but only one
pressure modulator valve). In the case of a 6S/5M
arrangement, the PMV controls both wheels on the
additional axle. The additional axle wheels would
receive equal brake pressure, based on the wheel that
is currently experiencing the most wheel slip.
Bendix
®
EC-30
™
ABS/
ATC
Controller
Bendix
®
EC-60
™
ABS/ATC Controllers
(left: Frame mount, and right: Cab Mount.)
Advanced Bendix
®
ABS uses yaw and
steering wheel
sensors to monitor
the vehicle motion.
See pages 39 and 40.
Speed Sensor
Mounting
Block
100 Tooth (typical)
Speed Sensor
Exciter Ring
(“tone” ring)
WS-24
™
Speed
Sensor (90 Deg.)
Hub
Assembly
S-Cam Brake
ABS Components Continued; Truck and Tractor ABS Operation