Troubleshooting And Testing; Abs Components; Bendix Ec-80 Controller; Sensors - PREVOST H3-41 Maintenance Manual

lock controlled operation during ABS system
failure.
The ABS system consists of two diagonally
related circuits, only the half of the system which
has sustained damage or other fault is switched
off (i.e. wheels return to normal non-ABS
braking). The other diagonal half remains under
full ABS control.
NOTE
ABS is active on service brake, transmission
retarder, engine brake, but is inactive on
emergency/parking brake.
NOTE
The ABS system is inoperative at speeds
under 4 mph (6 km/h). Illumination of ABS
telltale indicator at these speeds is normal.
CAUTION
Disconnect the ECU or pull the ABS fuse
before towing vehicle.
22.1

TROUBLESHOOTING AND TESTING

For detailed information, troubleshooting and
testing refer to Bendix booklet "Bendix Service
Data EC80 ESP Controller (SD-13-4986)" found
on the Technical Publications USB flash drive
and web site.
22.2

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.
22.3

BENDIX EC-80 CONTROLLER

This control unit, also known as ABS module, is
located in the front electrical and service
compartment. 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
SECTION 12: BRAKE AND AIR SYSTEM
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 49: ABS ECU LOCATION
CAUTION
In order to protect the ABS electronic control
unit from voltage surges, always disconnect
before performing any welding procedure on
vehicle.
22.4

SENSORS

The sensors are mounted on the front and drive
axle wheel hubs (Figure 35). The inductive
sensors consist essentially of a permanent
magnet with a round pole pin and a coil. The
rotation of the toothed wheel alters the magnetic
flux picked up by the coil, producing an
alternating voltage, the frequency of which is
proportional to wheel speed. When wheel speed
decreases, magnetic flux decreases proportion-
ately. Consequently, the electronic control unit
will command the solenoid control valve to
decrease the pressure at the corresponding
brake chamber.
PA1621 Maintenance Manual All Series | Revised June 2020 45