Bendix Commercial Vehicle Systems EC-80 ABS ATC SD - Manual (Page 7)

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The ECU will illuminate the ATC indicator lamp whenever
ATC is disabled due to a Diagnostic Trouble Code.
Trailer ABS Indicator Lamp Operation
Certain models of the ECU will control the Trailer ABS
indicator lamp when a PLC signal (SAE J2497) from a
trailer ABS ECU is detected.
Pressure Modulator Valve Chuff Test
Bendix ® EC‑80 ™ controllers will perform a Bendix‑patented
Pressure Modulator Valve (PMV) Chuff Test. The Chuff
Test is an electrical and pneumatic PMV test that can assist
maintenance personnel in verifying proper PMV wiring and
installation.
With brake pressure applied, a properly installed PMV will
perform one sharp audible exhaust of air by activating the
hold solenoid twice and the release solenoid once. If the
PMV is wired incorrectly, it will produce two exhausts of
air, or none at all.
The Bendix
EC‑80 controller will perform a PMV chuff test
on all installed modulators in the following order:
• Steer Axle Right PMV
• Steer Axle Left PMV
• Drive Axle Right PMV
• Drive Axle Left PMV
• Additional Axle Right PMV
• Additional Axle Left PMV
The pattern will then repeat itself. See Figure 6.
The ECU will not perform the PMV Chuff Test when wheel
speed sensors show that the vehicle is in motion.
Driver
Right Steer
Left Steer
Right
Additional
Left
Additional
Right Drive
Left Drive
FIGURE 6 - VEHICLE ORIENTATION (TYPICAL)
ABS OPERATION
Bendix ® ABS uses wheel speed sensors, ABS modulator
valves, and an ECU to control either four or six wheels of
a vehicle. By monitoring individual wheel turning motion
during braking, and adjusting or pulsing the brake pressure
at each wheel, the Bendix EC‑80 controller is able to
optimize slip between the tire and the road surface. When
excessive wheel slip, or wheel lock‑up, is detected, the
Bendix EC‑80 controller will activate the pressure modulator
valves to simulate a driver pumping the brakes. However,
the Bendix EC‑80 controller is able to pump the brakes on
individual wheels (or pairs of wheels), independently, and
with greater speed and accuracy than a driver.
Steer Axle Control
Although both wheels of the steer axle have their own wheel
speed sensor and pressure modulator valve, the Bendix
EC‑80 controller blends the applied braking force between
the two steering axle brakes. This Bendix‑patented brake
application control, called Modified Individual Control (MIC),
is 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).
Single Drive Axle Control (4x2 Vehicle)
For vehicles with a single rear drive axle (4x2), the brakes
are operated independently by the Bendix EC‑80 controller,
based on the individual wheel behavior.
Dual Drive Axle Control (4S/4M Configuration)
For vehicles with dual drive axles (6x4) using a 4S/4M
configuration, one ABS modulator controls both right-side
rear wheels, and the other modulator controls both left‑
side rear wheels. Both wheels on each side receive equal
brake pressure during an ABS stop. The rear wheel speed
sensors must be installed on the axle with the lightest load.
Dual Rear Axle Control (6S/6M Configuration)
For vehicles with dual rear axles (6x4, 6x2) using a 6S/6M
configuration, the rear wheels are controlled independently.
Therefore, brake application pressure at each wheel is
adjusted according to the individual wheel behavior on
the road surface.
6x2 Vehicles with 6S/5M Configuration
6x2 vehicles can utilize a 6S/5M configuration, with the
additional axle (a non‑driven rear axle) having two sensors,
but only one pressure modulator valve. In this case, 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.