Ontario Z Air Brake Endorsement Practice Test 2026: Practice test 3

Practice test 3 of 3 for the Ontario Z Air Brake Endorsement Practice Test: 20 more questions with answers and explanations.

Commercial vehicle
Ontario
70 questions
Checked October 10, 2026

Question 1 of 20
Which situation is most likely to cause severe brake fade?
- Using the engine brake on a short hill with an empty trailer
- A long downhill run with a heavy load at too high a speed
- Parking overnight in very cold weather with the spring brakes on
- Driving slowly on a flat road in town with many stops
Show answer
Answer: B. A long downhill run with a heavy load at too high a speed
Long descents, overloading and too much speed can overheat the brakes so badly that you cannot stop.
Question 2 of 20
What helps reduce brake heat on long downgrades?
- Shifting to neutral
- Pumping the brake pedal quickly
- Using an engine brake or retarder
- Turning off the air compressor
Show answer
Answer: C. Using an engine brake or retarder
Engine brakes and retarders slow the vehicle without heating the service brakes.
Question 3 of 20
In a dual air brake system, what happens if one circuit fails?
- All the brakes release at once and cannot be applied
- The trailer uncouples automatically from the tractor
- The other circuit should still be able to stop the vehicle
- The engine shuts off and the vehicle coasts to a stop
Show answer
Answer: C. The other circuit should still be able to stop the vehicle
Dual systems split air into primary and secondary circuits so one can still stop the vehicle if the other fails.
Question 4 of 20
In a dual air system, where does air go after the supply (wet) tank?
- Into the fuel tank to help push the fuel
- Straight to the exhaust, then out of the vehicle
- Into the primary and secondary (dry) tanks
- Back into the compressor to be pumped again
Show answer
Answer: C. Into the primary and secondary (dry) tanks
Air from the supply tank is split into the primary and secondary dual-service tanks.
Question 5 of 20
What does the air dryer do?
- Dries the tires after driving through rain
- Removes moisture before air enters the supply tank
- Measures the air pressure in each tank
- Heats the brake drums so they work in winter
Show answer
Answer: B. Removes moisture before air enters the supply tank
The air dryer removes moisture before the air reaches the supply tank.
Question 6 of 20
What is an alcohol evaporator for?
- To add alcohol vapour to the air and reduce freezing in the system
- To test the driver's breath for alcohol before starting
- To cool the engine on long, steep hills
- To clean the windshield in freezing weather
Show answer
Answer: A. To add alcohol vapour to the air and reduce freezing in the system
An alcohol evaporator puts alcohol vapour into the air to help stop moisture freezing in the lines and valves.
Question 7 of 20
Why is the supply tank called the wet tank?
- It collects most of the moisture and oil from the compressed air
- It is mounted under the fuel tank and gets wet in rain
- It is filled with water on purpose to cool the air
- It holds the windshield washer fluid for the cab
Show answer
Answer: A. It collects most of the moisture and oil from the compressed air
The supply tank receives air first and collects most of the moisture and oil.
Question 8 of 20
What does the one-way check valve do?
- Stops air from flowing back out of a tank
- Lets air flow both ways freely
- Releases air when pressure is high
- Applies the parking brake
Show answer
Answer: A. Stops air from flowing back out of a tank
A one-way check valve lets air into a tank but prevents it from flowing back out.
Question 9 of 20
What is the job of the tractor protection valve?
- To keep the tractor's air if the trailer is disconnected or breaks away
- To control the trailer's lights and turn signals
- To measure the trailer's weight before you drive
- To protect the tractor's paint from stones thrown by the trailer
Show answer
Answer: A. To keep the tractor's air if the trailer is disconnected or breaks away
The tractor protection valve prevents air loss from the towing vehicle when no trailer is attached or the trailer lines fail.
Question 10 of 20
What does the trailer supply valve control knob usually look like?
- A yellow, diamond-shaped knob
- A red, eight-sided push-pull knob
- A blue, round knob
- A green toggle switch
Show answer
Answer: B. A red, eight-sided push-pull knob
The trailer supply valve has a red, eight-sided push-pull knob.
Question 11 of 20
Gladhands connect the air lines between tractor and trailer. Which colour is the supply (emergency) line?
- Red
- Black
- Blue
- Green
Show answer
Answer: A. Red
Red gladhands are for the supply (emergency) line and blue are for the service line.
Question 12 of 20
What do the brake chambers do?
- Remove water and oil from the compressed air
- Turn air pressure into force on the push rod
- Store extra air for the horn and the seats
- Cool the brakes by blowing air on the drums
Show answer
Answer: B. Turn air pressure into force on the push rod
Air enters the chamber and pushes a diaphragm, which moves the push rod.
Question 13 of 20
What is a slack adjuster?
- A lever that links the push rod to the brake camshaft
- A spring inside the chamber that holds the parking brake
- A gauge on the dashboard that shows brake wear
- A valve that lets out extra air when pressure is too high
Show answer
Answer: A. A lever that links the push rod to the brake camshaft
The slack adjuster connects the push rod to the camshaft and increases the braking force.
Question 14 of 20
What are foundation brakes?
- The brake parts at each wheel, such as drums and shoes
- The concrete pads that trucks park on at terminals
- The brakes on the trailer's landing gear legs
- The engine brake that slows the vehicle on hills
Show answer
Answer: A. The brake parts at each wheel, such as drums and shoes
Foundation brakes are the wheel-mounted parts, such as drums or rotors and shoes or pads, worked by the air system.
Question 15 of 20
What applies the spring brakes?
- The driver's foot on the pedal
- A large spring, which air pressure holds back
- Air pressure pushing on the diaphragm
- Hydraulic fluid
Show answer
Answer: B. A large spring, which air pressure holds back
Spring brakes are applied by a strong spring and released by air pressure, so they apply when air is lost.
Question 16 of 20
What are the service brakes used for?
- Parking overnight only
- Emergency stops only
- Holding the trailer while coupling only
- Normal stopping, applied with the brake pedal
Show answer
Answer: D. Normal stopping, applied with the brake pedal
Service brakes are the brakes you use for normal stops, applied with the pedal.
Question 17 of 20
What does it mean if a spring brake chamber is caged?
- It has been filled with oil to stop it from rusting
- It is locked so no one can steal the brake parts
- It has a metal cover to keep out snow and road salt
- Its spring is held back by a caging bolt, so it will not apply
Show answer
Answer: D. Its spring is held back by a caging bolt, so it will not apply
A technician can cage the spring with a bolt, for example to move a vehicle in an emergency. The protruding bolt shows it is caged.
Question 18 of 20
Why should you never try to take apart a spring brake chamber?
- The spring is under very high tension and can injure you
- Opening it voids the trailer's registration
- It is full of hot oil that can burn your hands
- It contains a sensor that records brake use
Show answer
Answer: A. The spring is under very high tension and can injure you
The spring in the chamber is under very high tension. Never try to service or repair it.
Question 19 of 20
What is a DD3 chamber?
- A spring brake chamber with a caging bolt, used only on trailers
- A bus and coach brake chamber with three air connections and no large spring
- A diesel fuel filter used on buses and motor coaches
- A double-diaphragm gauge that shows two pressures at once
Show answer
Answer: B. A bus and coach brake chamber with three air connections and no large spring
DD3 chambers are used on buses and coaches. They have three air connections and no large power spring.
Question 20 of 20
You find an air brake defect during your inspection. What does Ontario law say about driving the vehicle?
- It is illegal to drive a defective vehicle, and you must report the defect
- You may drive it if the load is light or the trailer is empty
- You may drive it if you drive carefully and below 50 km/h
- You may drive it for up to 7 days before getting it fixed
Show answer
Answer: A. It is illegal to drive a defective vehicle, and you must report the defect
Drivers must report defects, and it is illegal to drive a defective vehicle.

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