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Published 01-14-2021 Control # 707-01
CARRIER
TMS9000-2 SERVICE MANUAL
rotation signals are sent to an Electronic Control Unit (ECU)
which sends signals to the ABS modulator valves if it detects
that a wheel has locked up or is about to lock up. The
modulator valves control the pressure in the brake assembly
air chambers.
Wheel rotation is determined by an electronic sensor (1),
(Figure 8-60) mounted in the brake spider. A signal is
generated by the sensor as high spots on a tooth wheel (2),
(Figure 8-60) pass by the sensor. The tooth wheel is either
mounted on or is part of the wheel hub.
ABS Indicator
The ABS control unit contains a self-testing program that is
engaged each time the ignition is turned on. The operator
can verify the testing by listening for the ABS modulator
valves actuating twice in series. To increase the sound, hold
down the foot brake pedal when the ignition is turned on.
NOTE:
The ECU will not perform the configuration test
when the speed sensors detect that the vehicle is
in motion.
If the indicator (1), (Figure 8-61) stays on, there is a problem
with the ABS. If the ABS indicator lights during driving, the
ABS self test has detected a fault in the system. The vehicle
can still be driven with a problem in the ABS. However, the
ABS will not be operating and standard air braking is in
effect.
ABS/ATC
ECU
Legend
Air Components
ABS/ATC
Components
Sensor Ring
Speed Sensor
ABS
Modulator
Valve
Relay
Valve
ABS
Modulator
Valve
ATC Valve
ABS
Modulator
Valve
Relay
Valve
Spring Brake
Relay Valve
FIGURE 8-59
FIGURE 8-60
1
2
Fo
r
Reference
Only