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Illinois CDL Air Brakes Practice Questions - Illinois CDL Air Brakes Knowledge Test Exam
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Question
1
of 25
QUESTION 1 / 25
What part of an air brake system compresses air and sends it toward the storage tanks?
Choose one answer below.
A
The air compressor
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B
The slack adjuster
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C
The brake drum
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D
The low-air warning device
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QUESTION 2 / 25
When tank pressure reaches about 125 psi, what should the air compressor governor normally do?
Choose one answer below.
A
Drain the wet tank
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B
Stop the compressor from pumping air
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C
Apply the spring brakes
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D
Turn on the low-air warning
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QUESTION 3 / 25
At about what pressure does the governor normally allow the compressor to start pumping again?
Choose one answer below.
A
20 psi
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B
55 psi
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C
100 psi
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D
150 psi
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QUESTION 4 / 25
What is the main purpose of the air compressor governor?
Choose one answer below.
A
To adjust brake shoe clearance
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B
To control when the compressor pumps air into the tanks
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C
To release water from the tanks automatically
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D
To reduce brake lag at the wheels
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QUESTION 5 / 25
If the compressor keeps pumping after normal cut-out pressure, what device protects the system by opening around 150 psi?
Choose one answer below.
A
The safety valve
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B
The stop light switch
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C
The foot valve
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D
The application pressure gauge
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QUESTION 6 / 25
Which condition should make a driver suspect a compressor, governor, or leak problem?
Choose one answer below.
A
The tanks build to cut-out and remain stable
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B
The compressor cycles very often or pressure builds slowly
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C
The parking brake knob stays out when parked
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D
The ABS lamp turns on briefly at startup
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QUESTION 7 / 25
Why must air tanks be drained regularly?
Choose one answer below.
A
To lower tire pressure
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B
To remove water and oil that can contaminate or freeze in the system
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C
To make spring brakes release faster
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D
To reset the ABS computer
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QUESTION 8 / 25
What is usually collected in the first air tank after the compressor, often called the supply or wet tank?
Choose one answer below.
A
Only clean dry air
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B
Water and compressor oil that should be drained
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C
Brake fluid from the master cylinder
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D
ABS fault codes
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QUESTION 9 / 25
What can happen if water in an air brake system freezes?
Choose one answer below.
A
The steering wheel locks automatically
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B
Air lines or valves may freeze, causing brake malfunction
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C
The compressor governor cut-out rises to 200 psi
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D
Brake drums become self-adjusting
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QUESTION 10 / 25
If a vehicle has automatic tank drains, what should the driver remember?
Choose one answer below.
A
Automatic drains eliminate all inspection duties
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B
Automatic drains should still be checked because they can fail
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C
Automatic drains replace the low-air warning device
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D
Automatic drains apply the parking brake
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QUESTION 11 / 25
What does an alcohol evaporator help prevent in some air brake systems?
Choose one answer below.
A
Brake lining wear
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B
Freezing of moisture in air lines and valves
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C
Excessive tire tread depth
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D
ABS wheel-speed sensor faults
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QUESTION 12 / 25
What should you do if you find a large amount of oil when draining an air tank?
Choose one answer below.
A
Ignore it because oil in tanks is always normal
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B
Have the compressor or air dryer system checked
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C
Add more alcohol to the fuel tank
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D
Disable the low-air warning device
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QUESTION 13 / 25
Before driving a vehicle with air brakes, why should you let pressure build to the normal operating range?
Choose one answer below.
A
Air pressure is needed to release spring brakes and operate service brakes reliably
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B
The engine cannot start until the tanks are full
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C
The ABS system charges the fuel injectors
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D
Brake drums must be filled with compressed air
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QUESTION 14 / 25
What warning is required when air pressure becomes dangerously low?
Choose one answer below.
A
A low air pressure warning signal the driver can see, often with a buzzer
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B
A green light showing the compressor is off
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C
A horn blast from outside the vehicle only
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D
A tire pressure lamp
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QUESTION 15 / 25
Under the CDL manual air-brake check, the low-air warning should activate before pressure drops below what value?
Choose one answer below.
A
20 psi
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B
55 psi
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C
100 psi
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D
150 psi
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QUESTION 16 / 25
What is a wig-wag in an air brake system?
Choose one answer below.
A
A type of S-cam
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B
A mechanical low-air warning arm that drops into the driver's view
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C
A trailer parking brake valve
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D
An automatic slack adjuster
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QUESTION 17 / 25
If the low-air warning comes on while you are driving, what should you do?
Choose one answer below.
A
Continue at highway speed until the next scheduled stop
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B
Stop safely as soon as possible and have the problem fixed
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C
Pump the brakes to build pressure
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D
Pull the parking brake valve immediately at speed
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QUESTION 18 / 25
During a pre-trip air brake test, how do you check the low-air warning?
Choose one answer below.
A
Build full pressure, turn electrical power on, and fan the brake pedal until the warning activates
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B
Drive at 20 mph and make a hard stop
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C
Drain only the fuel tank
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D
Pull the ABS fuse and watch the dash
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QUESTION 19 / 25
What does a low-air warning tell you about available braking?
Choose one answer below.
A
The system is at normal full pressure
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B
Air pressure is becoming too low for safe continued operation
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C
ABS has shortened the stopping distance
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D
The service brakes are adjusted perfectly
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QUESTION 20 / 25
In a dual air system, where is the low-air warning threshold measured?
Choose one answer below.
A
Only in the tire with the lowest pressure
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B
In the tank or circuit with the lowest air pressure
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C
Only in the fuel tank
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D
Only at the ABS module
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QUESTION 21 / 25
What is the maximum air loss allowed in one minute for a single vehicle with brakes released during the static leakage test?
Choose one answer below.
A
1 psi
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B
2 psi
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C
4 psi
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D
6 psi
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QUESTION 22 / 25
What is the maximum air loss allowed in one minute for a combination vehicle with brakes released?
Choose one answer below.
A
2 psi
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B
3 psi
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C
5 psi
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D
8 psi
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QUESTION 23 / 25
What is the maximum air loss allowed in one minute for a single vehicle with the brake pedal fully applied?
Choose one answer below.
A
2 psi
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B
3 psi
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C
4 psi
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D
10 psi
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QUESTION 24 / 25
What is the maximum air loss allowed in one minute for a combination vehicle with the brake pedal fully applied?
Choose one answer below.
A
2 psi
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B
3 psi
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C
4 psi
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D
6 psi
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QUESTION 25 / 25
Which setup is correct for the applied air leakage test?
Choose one answer below.
A
Engine off, brakes released, and no pedal pressure
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B
Engine off, parking brakes released, and service brake pedal fully applied
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C
Engine running at highway rpm with parking brakes applied
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D
Vehicle moving at 5 mph
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