Heavy Duty Truck Systems – Chapters 25–30 & 33 Combined – Lecture Summaries & Practice
Questions Compilation
When does an ATC light illuminate? - ANS ✔✔whenever a spinout condition occurs
What type of tractor ABS is required to support most antirollover and directional stability
control electronics? - ANS ✔✔6S/6M
Which of the following provides the most critical input signal to the ABS module? - ANS
✔✔wheel speed sensor
Which of the following is the control component in an ABS modulator valve? - ANS ✔✔solenoid
or motor
Which of the following ABS channel configurations is required in a truck equipped with stability
control electronics (SCE)? - ANS ✔✔6S/6M
What is the maximum modulation speed of a typical air brake ABS? - ANS ✔✔7 times per
second
Technician A says that in a true EBS, the brake pedal does no more than produce an electrical
signal to the EBS control module. Technician B says that current FMVSS 121 legislation requires
that when EBS is used on North American highways, it is in addition to pneumatic controls. Who
is correct? - ANS ✔✔both A and B
Which of the following is the main output device on a truck ABS? - ANS ✔✔modulator assembly
Which of the following is true of the ABS tractor warning light? - ANS ✔✔It illuminates when
the ignition key is turned on.
,Which of the following is likely to occur if an ABS ceases to function? - ANS ✔✔ABS shuts down
and a driver warning light comes on.
Technician A says that air brake ABS can be modulated at much higher speeds than hydraulic
ABS because of the compressibility of air. Technician B says that a truck air brake ABS control
module can think (clock speed) at a frequency of 200 times per second. Who is correct? - ANS
✔✔Technician B only
Which of the following statements best describes how ABS prevents brake lockup? - ANS
✔✔ABS monitors wheel speed and reduces service pressure when lockup is imminent.
Before testing a dual-drive axle truck equipped with ATC on a chassis dynamometer, what
should be done? - ANS ✔✔ATC must be disabled.
An ABS light displays fault codes that are not interpreted in the OEM service literature. Which of
the following is the likely problem? - ANS ✔✔defective ECM
Why do some ABS ECUs contain two microprocessor units? - ANS ✔✔one microprocessor acts
as a fail-safe backup to the other
Which of the following best describes the type of sensor used to signal wheel speed data to an
ABS module? - ANS ✔✔pulse generator
Which of the following air brake system components functions as a lever? - ANS ✔✔the slack
adjuster
Which of the following components sets the system cut-in and cut-out pressures? - ANS ✔✔the
governor
, What is the function of a system safety pop-off valve? - ANS ✔✔It relieves pressure from the
supply tank in the event of governor cut-out failure.
The function of the foot valve or dual-circuit application valve is to: - ANS ✔✔meter air to the
service brake circuit
The potential energy of an air brake system is: - ANS ✔✔compressed air
Which of the following components is a requirement on every air tank? - ANS ✔✔a draincock
What is the minimum total storage volume of air dedicated to brake system requirements of an
air brake-equipped trailer? - ANS ✔✔eight times total chamber volume
The function of an air brake chamber is to: - ANS ✔✔convert the energy of compressed air into
mechanical force
An air brake equipped truck is traveling on a highway at 60 mph and the driver makes a service
brake application. Which of the following should be true in all of the spring brake chambers on
the vehicle? - ANS ✔✔Both the service and hold-off chambers are charged with air.
Technician A says that automatic slack adjusters can improve brake balance and reduce
downtime and maintenance costs. Technician B says that automatic slack adjusters should not
be adjusted after installation. Who is correct? - ANS ✔✔Technician A only
When an inversion valve becomes functional during a brake failure, what force is used to brake
the vehicle? - ANS ✔✔spring pressure
Which of the following determines the amount of leverage gained by a slack adjuster? - ANS
✔✔the slack adjuster length
Questions Compilation
When does an ATC light illuminate? - ANS ✔✔whenever a spinout condition occurs
What type of tractor ABS is required to support most antirollover and directional stability
control electronics? - ANS ✔✔6S/6M
Which of the following provides the most critical input signal to the ABS module? - ANS
✔✔wheel speed sensor
Which of the following is the control component in an ABS modulator valve? - ANS ✔✔solenoid
or motor
Which of the following ABS channel configurations is required in a truck equipped with stability
control electronics (SCE)? - ANS ✔✔6S/6M
What is the maximum modulation speed of a typical air brake ABS? - ANS ✔✔7 times per
second
Technician A says that in a true EBS, the brake pedal does no more than produce an electrical
signal to the EBS control module. Technician B says that current FMVSS 121 legislation requires
that when EBS is used on North American highways, it is in addition to pneumatic controls. Who
is correct? - ANS ✔✔both A and B
Which of the following is the main output device on a truck ABS? - ANS ✔✔modulator assembly
Which of the following is true of the ABS tractor warning light? - ANS ✔✔It illuminates when
the ignition key is turned on.
,Which of the following is likely to occur if an ABS ceases to function? - ANS ✔✔ABS shuts down
and a driver warning light comes on.
Technician A says that air brake ABS can be modulated at much higher speeds than hydraulic
ABS because of the compressibility of air. Technician B says that a truck air brake ABS control
module can think (clock speed) at a frequency of 200 times per second. Who is correct? - ANS
✔✔Technician B only
Which of the following statements best describes how ABS prevents brake lockup? - ANS
✔✔ABS monitors wheel speed and reduces service pressure when lockup is imminent.
Before testing a dual-drive axle truck equipped with ATC on a chassis dynamometer, what
should be done? - ANS ✔✔ATC must be disabled.
An ABS light displays fault codes that are not interpreted in the OEM service literature. Which of
the following is the likely problem? - ANS ✔✔defective ECM
Why do some ABS ECUs contain two microprocessor units? - ANS ✔✔one microprocessor acts
as a fail-safe backup to the other
Which of the following best describes the type of sensor used to signal wheel speed data to an
ABS module? - ANS ✔✔pulse generator
Which of the following air brake system components functions as a lever? - ANS ✔✔the slack
adjuster
Which of the following components sets the system cut-in and cut-out pressures? - ANS ✔✔the
governor
, What is the function of a system safety pop-off valve? - ANS ✔✔It relieves pressure from the
supply tank in the event of governor cut-out failure.
The function of the foot valve or dual-circuit application valve is to: - ANS ✔✔meter air to the
service brake circuit
The potential energy of an air brake system is: - ANS ✔✔compressed air
Which of the following components is a requirement on every air tank? - ANS ✔✔a draincock
What is the minimum total storage volume of air dedicated to brake system requirements of an
air brake-equipped trailer? - ANS ✔✔eight times total chamber volume
The function of an air brake chamber is to: - ANS ✔✔convert the energy of compressed air into
mechanical force
An air brake equipped truck is traveling on a highway at 60 mph and the driver makes a service
brake application. Which of the following should be true in all of the spring brake chambers on
the vehicle? - ANS ✔✔Both the service and hold-off chambers are charged with air.
Technician A says that automatic slack adjusters can improve brake balance and reduce
downtime and maintenance costs. Technician B says that automatic slack adjusters should not
be adjusted after installation. Who is correct? - ANS ✔✔Technician A only
When an inversion valve becomes functional during a brake failure, what force is used to brake
the vehicle? - ANS ✔✔spring pressure
Which of the following determines the amount of leverage gained by a slack adjuster? - ANS
✔✔the slack adjuster length
