Service manual

Group 59 Anti-Lock Brake System (Bendix) Design and Function
Traction Control System (TCS)
The ABS on a vehicle may also be configured for trac-
tion control. The Traction Control System (TCS) uses the
same wheel sensors as the ABS to determine if one set
of drive wheels is spinning much more rapidly than those
on the other side. If the TCS determines that a wheel is
spinning and the vehicle speed is below 40 km/h (25
mph), it opens the relay valve to apply some braking
force to stop the wheels from spinning.
If the vehicle speed is above 40 km/h (25 mph), the sys-
tem sends a signal to the Engine Electronic Control Unit
(EECU) to reduce the engine rpm to be consistent with
vehicle speed. This action helps reduce the amount of
wheel spin and gives the driver greater vehicle control.
The TCS option includes an additional switch. In the
normal (down) position, the TCS operates normally to in-
crease traction to the spinning wheels. When placed in
the off (up) position, the TCS does not apply braking
force to the spinning wheels.
There is a yellow TCS warning light on the instrument
cluster. The light has several functions. If the TCS switch
is in the off position, the TCS light will come on to re-
mind the driver that TCS is off. If TCS is not installed,
the light will blink once per second while drive wheel
spin is detected. If TCS is installed, the light will come
on while the TCS system is controlling wheel spin. The
lamp will also come on and stay on if a fault is detected
in the TCS circuits.
W3001336
TCS switch
ABS Self Tests
The Bendix ABS has a variety of self monitoring fea-
tures. When the ignition switch is ON, the ABS warning
light in the instrument cluster energizes to tell the opera-
tor that the system is powered and that it is conducting
self tests. There are two tests performed by the system
at this point.
The first test energizes and de-energizes the modulator
isolation solenoids to ensure the circuits and valves are
functional. In the second test, the operation of the ex-
haust portion of the modulator valves is tested, also by
energizing and de-energizing them.
One additional self-test is performed by the ABS. This
test occurs once the vehicle begins moving. As the vehi-
cle starts to speed up from a standstill, the ABS monitors
the output from each of the wheel speed sensors and
verifies that they are reading correctly, and within the
correct range compared with the other wheels. If the test
is satisfactory, the ABS warning light goes out when the
vehicle speed reaches approximately 11 km/h (7 mph). If
the test is not satisfactory, the warning light will remain lit.
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