28
Brakes & Wheels
Figure 7-9, Anti-Lock Brake System
ECU
ABS
MODULATION
VALVES
ABS
MODULATION
VALVES
TOOTH WHEEL SENSOR
TOOTH WHEEL
SENSOR
PNEUMATIC
ELECTRIC
20-500-33
ANTI-LOCK BRAKING SySTEM OPERATION
The Anti-Lock Braking System (ABS) is an electronic system that monitors and controls wheel speed
during braking. See Figure 7-
9
. This illustration below shows a schematic view, not location. The ABS
ECU (electronic control unit) is frame mounted, usually located behind the rear suspension. If a wheel
starts to lock up during braking, the ABS will reduce air pressure to that wheel’s brake to keep all wheels
turning at the same speed to maintain the vehicle in a straight line. When the wheel speed enters the
stable region again, the pressure is automatically increased.
There is an ABS warning lamp located on the light bar that will light if the system is malfunctioning. If
the brakes are not operating properly and the ABS warning lamp is not lit, the problem is probably in the
brake system, not the ABS.
ABS Components
Tooth Wheel
A tooth wheel, located on each wheel hub, rotates with the wheel and provides the means of measuring
the speed of the wheel.
Sensor
A sensor observes the tooth wheel rotation and generates electronic pulses that indicate wheel speed.
The front wheel sensors are mounted on the steering knuckles. The rear wheel sensors are mounted in a
block attached to the axle housing.
Summary of Contents for LOW FLOOR
Page 18: ...Specifications 18...
Page 58: ...Preventive Maintenance 58...
Page 110: ...Engine 110...
Page 138: ...Transmission Driveline Rear Axle 138...
Page 182: ...Suspension 182...
Page 260: ...Air System 260...
Page 420: ...Electrical System 420 Deutsch DT Series Connectors...
Page 421: ...Electrical System 421...
Page 422: ...Electrical System 422 Deutsch HD 10 Series Connectors...
Page 423: ...Electrical System 423...
Page 424: ...Electrical System 424 Deutsch HD 30 Series Connectors...
Page 425: ...Electrical System 425...
Page 442: ...Heating Air Conditioning 442...
Page 492: ...Body and Interior 492 Figure 11 33 USSC Seat Assembly...
Page 493: ...Body and Interior 493 Figure 11 34 USSC Seat Suspension Assembly...
Page 495: ...Body and Interior 495 Figure 11 37 Seat Air Connections...