190402d Air Antilock Brake Systems
What does R. S. C. stand for?
Roll stability control.
What general precautions when you work on, test or disable an A. B. S. must be followed?
Always wear personal protection equipment as required. Use suitable stands to support the vehicle. Release system air pressure before loosening or removing any air system component. Release system hydraulic brake pressure before loosening or removing any component. Apply the parking brakes and chock the wheels. Lock out the vehicle as per shop policy.
What kind of signal does the wheel speed sensor send?
An electric pulse between zero and four hundred hertz.
What are some negative conditions that can affect braking quality and subsequent vehicle handling?
An unevenly loaded vehicle. Front-to-rear or side-to-side uneven tire inflation. Differences in tire tread conditions. Mixing different brands of tires. Unevenly adjusted brakes. Defective brakes at one or more wheels. Sagging or otherwise damaged suspension components. Variable road conditions at one or more tires. Excessive speed. An overloaded vehicle. Wheel alignment problems.
What does A. B. S. stand for?
Antilock brake system.
What two truck systems work with R. S. C. to help reduce reaction time when needed?
Antilock brake system. Electronic engine management.
When the offroad switch is activated, the E. C. U. recognizes the change of operation and the speed programmed to activate the modulators is adjusted to allow a slight lockup of the wheels. How does this help stopping?
As the wheels lock up in these conditions, material builds up in front of the wheel, acting as a wedge. This wedge assists in slowing and stopping the vehicle.
What does A. T. C. stand for?
Automatic traction control.
In the normal braking event what are the solenoids doing in an A. B. S. modulator valve?
Both solenoids are de-energized or inactive.
In the exhaust event what are the solenoids doing in an A. B. S. modulator valve?
Both solenoids are energized or active.
What does a four-channel A. B. S. system refer to?
Channels refer to the number of circuits that are modulated; that is, to the number of modulators on the unit.
When you work on any vehicle with electronics on it, you must use the what general precautions?
Disconnect the batteries and/or E. C. U. before welding. Do not disconnect any electrical component with the system powered. Use only high impedance meters for voltage testing. Never probe conductor insulation. Keep excessive heat away from electronic components.
What does E. B. S. stand for?
Electronic brake system.
What does E. S. C. stand for?
Electronic stability control.
The order in which the ECU instructs the modulator valve to control air pressure is what?
Exhaust. Hold. Reapply.
Which component allows for differential braking of the steer axle to help prevent spinout or jackknife conditions?
Front axle control valve.
What three additional components does the E. S. C. use?
Front axle control valve. Steering angle sensor. Brake demand pressure sensor.
What are the two primary functions of roll stability control?
Help control vehicle stability. Limit rollover conditions.
What is the A. T. C. indicator/warning lamp used for?
Indicate to the operator that the system is active. Indicate that dyno-mode is activated. Indicate that the driver has activated the deep snow/mud switch.
Where are electronic control modules mounted on truck/tractors, buses and trailers?
Inside the truck cab or bus baggage compartment, mounted to the frame or cross member or attached directly to the trailer air reservoir.
During a braking situation, what is the flow in the A. T. C. valve?
It allows the brake pressure to pass out the delivery port.
To achieve threshold braking on an air A. B. S. system, the E. C. U. can cycle the appropriate modulator valves how fast?
It can cycle through these conditions several times a second.
A human can only perform brake pumping one to three times per second, but antilock system electronics can perform how fast?
It can make corrections up to one hundred times per second.
What are other names for the tone ring?
It is also called tooth wheel. Tooth ring. Or exciter ring.
Where is the A. T. C. valve located?
It is located between the brake (treadle) valve and the service brake relay at the rear drive axles.
Where is the R. S. C. valve located?
It is located in the secondary air system between the treadle valve and the tractor protection valve.
What kind of engine control does the A. T. C. system need to reduce torque to the drive wheels?
It must be electronically controlled.
If a wheel spin occurs at a higher speed (typically above forty kilometers per hour), the A. T. C. system uses?
It uses torque reduction only. Differential braking at these speeds would lead to excessive driveline shock loading and foundation brake temperature.
What three things does the A. B. S. help when operating?
Maintains control. Reduces stopping distances. Saves on tire flat spotting.
Does the modulator valve send and receive signals to and from the ECU?
No, the modulator does not send signals to the E. C. U.
During a normal braking situation, what is the antilock E. C. U. doing?
Only monitoring wheel speeds.
A tandem axle truck, tractor or bus has air ride suspension and a 4S/4M system. Which axle would typically have wheel speed sensors?
Rear drive axle.
What are the responses the R. S. C. system can use to slow the vehicle?
Reduce engine torque. Engage engine/driveline retarders. Apply brake pressure to the drive axle brakes. Modulate brake pressure to the trailer brakes.
What is the difference between roll stability control and electronic stability control?
Roll stability control does not offer direction control of the vehicle.
What additional component is added to a vehicle equipped with E. S. C?
Steering angle sensor.
Engine, exhaust and driveline retarders have sufficient braking capabilities to produce a wheel lockup condition how does this affect the A. B. S. System?
The A. B. S. system, to be effective, must be able to turn them off.
What must be done on a dynamometer test when a vehicle is equipped with A. T. C?
The A. T. C. must be disabled.
What does the E. C. U. monitor in order to respond to excessive speed on a curve?
The E. C. U. measures the lateral or side-to-side movements of the vehicle.
Where is the E. S. C. located?
The E. S. C. module is usually located under the cab in the centre of the frame rail.
As of March 1, 1998, where does the trailer antilock E. C. U. receives its power?
The auxiliary pin of the trailer cord.
In the holding braking event what are the solenoids doing in an A. B. S. modulator valve?
The exhaust solenoid is de-energized. The supply solenoid remains energized.
Typically, on a tandem axle assembly with spring suspension which axle off-load first?
The front axle off-loads first.
Where is the air A. B. S. modulator valve located in the front of a vehicle?
The modulator is between the quick release (or ratio valve) and the air brake chamber.
Where is the air A. B. S. modulator valve located in the rear of a vehicle?
The modulator is between the relay valve and the air brake chamber.
Typically, on a tandem axle assembly with air suspension which axle off-load first?
The rear axle off-loads first.
On initial start-up, the A. B. S. warning lamp lights up and stays on to indicate to the operator that?
The system could be functioning properly, but must be driven above five to ten kilometers per hour to confirm. There is an existing fault code.
A yaw sensor and an accelerometer are located inside the E. S. C. module what do they monitor?
The yaw sensor measures rotational forces in order to detect jackknifing or spinout. The accelerometer measures lateral acceleration during cornering in order to sense whether a rollover condition is occurring.
When off-road is activated by the operator, this A. T. C. feature allows the wheels, which are monitored and controlled by the ABS system, to spin slightly faster than normally acceptable or programmed in the ECU because?
This allows the wheels to throw off mud and debris to clean the treads and improve traction.
How do you adjust the wheel speed sensor?
To adjust the running clearance of the sensor and tone ring, push the sensor firmly into the holder until the face of the sensor contacts the tone ring. Once the wheel rotates one revolution, the movement of the tone ring causes the sensor to slide back slightly in the spring retainer, thereby setting the running clearance.
What are the two primary functions of an A. B. S. system?
To help the operator maintain control throughout the braking application under less than ideal conditions. To improve the chances of reducing overall stopping distances.
What does V. D. C. stand for?
Vehicle dynamic control.
What does V. S. C. stand for?
Vehicle stability control.
The wheel speed sensor has a AC signal it has two components what are they?
Voltage, which is measured in amplitude. Frequency, which is measured in hertz.
What is the the tone ring typically part of or attached to?
Wheel hub.
