Section 12: BRAKE AND AIR SYSTEM
PA1562
27
CAUTION
Disconnect the ECU or pull the ABS fuse
before towing vehicle.
31.1 TROUBLESHOOTING AND TESTING
For troubleshooting and testing of the vehicle's
anti-lock braking system, refer to Meritor Wabco
Maintenance Manual MM-0112: “Anti-Lock
Braking System (ABS) for Trucks, Tractors and
Buses", at the end of this section. Use
dashboard Message Center Display (MCD)
Diagnostic Mode for troubleshooting and repair.
31.2 AUTOMATIC TRACTION CONTROL
(ATC) – ELECTRONIC STABILITY PROGRAM
(ESP)
In addition to the ABS function, vehicle may be
equipped with an advanced model of Bendix
EC-60 controller to provide an Automatic
Traction Control (ATC) feature. Bendix ATC
can improve vehicle traction during acceleration,
and lateral stability while accelerating through
curves. ATC utilizes Engine Torque Limiting
(ETL) where the ECU communicates with the
engine’s controller and/or Differential Braking
(DB) where individual wheel brake applications
are used to improve vehicle traction.
The EC-60 advanced model controller also
provides ABS-based stability features referred to
as ESP
®
Electronic Stability Program.
NOTE
Vehicles equipped with the ATC/ESP system
have one more modulator valve and two
additional sensors located on the tag axle
wheels (6S/5M). Basic ABS consists of 4
sensors and 4 modulator valves (4S/4M).
CAUTION
Even with ESP-equipped vehicles, the driver
remains responsible for ensuring vehicle
stability during operation.
DANGER
ESP may reduce the vehicle speed
automatically.
DANGER
ESP can make the vehicle decelerate
automatically. ESP can slow the vehicle with
or without the operator applying the brake,
and even when the throttle is being
applied.
31.3 ABS COMPONENTS
The main components of the ABS system are
listed hereafter. Refer to each component for its
specific function in the system and for proper
maintenance.
31.3.1 Electronic Control Unit (ECU)
This control unit is located in the front electrical
compartment, (refer to figure 44 for location).
According to the data transmitted by the sensors
(number of pulses/sec is proportional to the
speed of each wheel), the electronic control unit
determines which wheel is accelerating or
decelerating. It then establishes a reference
speed (average speed) from each wheel data,
and compares the speed of each wheel with this
reference speed to determine which wheel is
accelerating or decelerating.
As soon as wheel deceleration or wheel slip
threshold values are exceeded, the electronic
control unit signals a solenoid control valve to
limit the excessive brake pressure produced by
the driver in the appropriate brake chamber.
Maintenance
No specific maintenance is required. The ECU is
not serviceable. When found to be defective,
replace.
FIGURE 44: ABS ECU LOCATION 06617
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