Troubleshooting guide

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Driver
Right Steer Axle
Left Steer Axle
Right Additional
Axle
Left Additional
Axle
Right Drive
Axle
Left Drive
Axle
Normal Braking
During normal braking, air brake pressure is delivered
through the ABS PMV and into the brake chamber. If
the ECU does not detect excessive wheel slip, it will not
activate ABS control, and the vehicle stops with normal
braking.
Retarder Brake System Control
On surfaces with low traction, application of the retarder
can lead to high levels of wheel slip at the drive axle
wheels, which can adversely affect vehicle stability. To
avoid this, some Bendix ECU controllers are designed to
switch off the retarder as soon as a lock-up is detected at
one (or more) of the drive axle wheels. In these cases,
when the ECU is placed in the ABS off-road mode, it will
switch off the retarder only when ABS is active on a steer
axle wheel and a drive axle wheel.
Optional ABS Off-Road Mode
When used on some off-road surfaces, (for example,
loose gravel), ABS provides superior vehicle steerability
and stability, however there is the potential for stopping
distances to be longer than without ABS. This is because
locked-up wheels on gravel, etc. tend to plow up the road
surface in front of the tires.
Bendix Premium ECUs have an optional ABS off-road
control mode that more effectively accommodates these
soft road conditions and shortens stopping distances
while maintaining optimal vehicle steerability and
stability. Care must be taken, however, not to use the
ABS off-road mode on normal, paved road surfaces
(since vehicle stability and steerability may be reduced),
so the ABS Indicator Lamp fl ashes to show the driver that
the ABS off-road mode is being used.
All-Wheel Drive (AWD) Vehicles
AWD vehicles with an engaged interaxle differential
(steer axle to rear axle)/AWD transfer case may have
negative effects on ABS performance. Optimum ABS
performance is achieved when the lockable differentials
are disengaged, allowing individual wheel control.
Premium ECUs can be programmed specifi cally for
this confi guration to control the differential lock/unlock
solenoid in the AWD transfer case. When programmed
to do so, the ECU will disengage the locked interaxle/
AWD transfer case during an ABS event and reengage it
once the ABS event has ended.
ATC Operation
ATC Functional Overview
Just as ABS improves vehicle stability during braking,
ABS systems with ATC improve vehicle stability and
traction during vehicle acceleration. The ATC function
uses the same wheel speed information and modulator
control as the ABS function. The ECU detects excessive
drive wheel speed, compares the speed of the front, non-
driven wheels, and reacts to help bring the wheel spin
under control. The ECU can be confi gured to use engine
torque limiting and/or differential braking to control wheel
spin. For optimal ATC performance, both methods are
recommended.
Differential Braking
Differential braking is automatically activated when drive
wheel(s) on one side of the vehicle are spinning, which
typically occurs on asphalt road surfaces with patches
of ice. The traction system will then lightly apply the
brake to the drive wheel(s) that are spinning. The vehicle
differential will then drive the wheels on the other side
of the vehicle. Differential braking is available at vehicle
speeds up to 25 MPH.
Truck and Tractor ABS Operation; ATC
Vehicle Axle Naming Convention