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Ontario Air Brake (Z) overview

Ontario Air Brake (Z): Air brake system tests

Pass and fail limits for the low-air warning, build-up time, governor settings, air-loss rates, tractor protection valve, trailer and spring brake tests and draining tanks.

  • 29 questions
  • Topic drill
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Air brake system tests · Question 1Score 0/0

Why might an older truck show lower governor settings than a new one?

Study reference: MTO Air Brake Handbook (online edition, Feb. 2026), Ch. 10 Inspecting Air Brake System Operation

All 29 questions in this test

Every question and its answer choices. The correct answers and explanations appear when you take the test above.

  1. Why might an older truck show lower governor settings than a new one?

    1. Cold weather lowers the settings over time
    2. Operating pressures have risen
    3. Old governors are always defective
    4. Older trucks use hydraulic governors

  2. A tractor is hauling a single semi-trailer. How much air loss per minute is allowed during the applied-brake test?

    1. 8 psi (55 kPa)
    2. 6 psi (41 kPa)
    3. 3 psi (21 kPa)
    4. 4 psi (28 kPa)

  3. During the air-loss test, how do you treat the first drop when you press the pedal?

    1. Add it to the result of the next minute
    2. Restart the test after each drop
    3. Ignore it; time after it settles
    4. Count it as part of the loss

  4. Which sign tells you the compressor has cut in?

    1. The low-air warning light comes on
    2. The yellow spring brake knob pops out
    3. Pressure starts to rise again
    4. The air dryer purges loudly

  5. For the build-up test, what engine speed is used?

    1. 600 to 900 rpm
    2. 1,200 to 1,500 rpm
    3. 300 to 500 rpm
    4. Full governed rpm

  6. The warning came on at 62 psi and went off at 68 psi as pressure rose. Is that a defect?

    1. Yes, it must go off at 55 psi
    2. Yes, it must come on at 80 psi
    3. No, on and off points can differ
    4. Yes, they must be identical

  7. What is the longest allowed build-up time from 85 to 100 psi?

    1. Five minutes
    2. Two minutes
    3. 30 seconds
    4. Ten minutes

  8. What is the recommended way to test automatic trailer spring brake application?

    1. Pull out the trailer supply valve
    2. Disconnect the line under pressure
    3. Pull the trailer hand valve
    4. Pump the pedal to zero air

  9. How should you secure the vehicle before the system operation tests?

    1. Any surface, as long as the ABS is on
    2. A downhill slope with the engine idling
    3. Trailer hand valve applied and nothing else
    4. Level ground, spring brakes on, chocks

  10. To test the low-air warning, what pressure should you start above?

    1. 145 psi (1000 kPa)
    2. 60 psi (414 kPa)
    3. 90 psi (621 kPa)
    4. 55 psi (380 kPa)

  11. During the low-air warning test, what must the ignition be?

    1. Off, with the engine stopped
    2. Off, with the battery disconnected
    3. On; the engine may run or be off
    4. On, with the engine at 1,200 rpm

  12. Testing the tractor protection valve, which valve position and line do you set up?

    1. Supply valve closed, service line disconnected
    2. Hand valve applied, gladhands joined
    3. Supply valve open, both lines connected
    4. Supply valve closed, supply line removed

  13. How can you confirm the trailer spring brakes have applied?

    1. Gently apply power to see if it holds
    2. Read the date on the trailer's annual decal
    3. Check that the trailer ABS lamp is off
    4. Look for frost forming on the gladhands

  14. How long should you drain the supply tank during the drain valve check?

    1. Until the low-air light comes on
    2. For exactly ten seconds
    3. Until pressure reaches 60 psi
    4. Until only clean air comes out

  15. How do you find the governor's cut-out pressure?

    1. Note where the warning light comes on
    2. Note where the safety valve opens
    3. Note where the gauges stop climbing
    4. Note where the spring brakes apply

  16. The low-air warning comes on at 50 psi. Does the vehicle pass?

    1. No, 55 psi is the minimum
    2. Only if it switches off again at 60 psi
    3. Yes, as long as the buzzer is loud
    4. Yes, anything above 40 psi passes

  17. Over which pressure range is build-up time measured?

    1. From 85 to 100 psi
    2. From 0 to 60 psi
    3. From 60 to 90 psi
    4. From 100 to 145 psi

  18. Before timing air build-up, what should you do if a trailer is attached?

    1. Drain the trailer tanks
    2. Open the trailer supply valve
    3. Close the trailer supply valve
    4. Apply the trailer hand valve

  19. While draining tanks, you see a lot of water from the secondary tank. What should you do?

    1. Add more alcohol to the evaporator
    2. Drain the supply tank last
    3. Nothing; it is always wet
    4. Report it; that is not normal

  20. You find oil in a tank other than the supply tank. What is the concern?

    1. Brake system contamination
    2. The compressor is running too cold
    3. The tank needs a larger drain valve
    4. Nothing; the oil lubricates the valves

  21. How do you lower air pressure for the low-air warning test?

    1. Pull out the trailer supply valve
    2. Open the supply tank drain valve
    3. Disconnect the trailer service gladhand
    4. Press and release the pedal repeatedly

  22. Which governor result makes the air brake system defective?

    1. Cut-in below 80 psi
    2. Cut-in at 100 psi
    3. Cut-out at 125 psi
    4. Cut-out 20 psi above cut-in

  23. For a tractor-trailer, whose spring brakes is it preferable to test for holding?

    1. The converter dolly's
    2. None; only service brakes are tested
    3. The towing vehicle's
    4. The rear trailer's only

  24. If you think the tractor has no anti-compounding valve, what should you do before applying the service brakes?

    1. Secure it and release spring brakes
    2. Run the engine at a high rpm
    3. Connect the trailer supply gladhand
    4. Open all of the tank drain valves

  25. In a doubles or triples combination, what air drop per minute is the upper limit?

    1. 5 psi (35 kPa)
    2. 8 psi (55 kPa)
    3. 4 psi (28 kPa)
    4. 6 psi (41 kPa)

  26. Air-loss test on a straight truck with brakes applied: what is the most pressure it may lose in one minute?

    1. 1 psi (7 kPa)
    2. 4 psi (28 kPa)
    3. 3 psi (21 kPa)
    4. 6 psi (41 kPa)

  27. During the tractor protection valve test, air blows out of the service line. What does it mean?

    1. The trailer brakes are applied
    2. The spring brakes need caging first
    3. The valve is working correctly
    4. That valve is defective

  28. How do you test that the spring brakes can hold the vehicle?

    1. Pump the pedal while they are applied
    2. Apply them while at highway speed
    3. Apply them, then pull gently in low gear
    4. Release them and coast down a hill

  29. For the air-loss test, what is the engine and pedal condition?

    1. Engine at 900 rpm, pedal half down
    2. Engine off, pedal held fully applied
    3. Engine off, pedal pumped
    4. Engine idling, pedal released

Air brake system tests: key rules to remember

Our summary of what the official handbook says on this topic, in our own words. Read it before or after the practice questions above, then check the original chapter. Read the official chapter ↗

Before testing

  • Park on level ground, apply the spring brakes and chock the wheels before starting.

Low air-pressure warning

  • Start above 90 psi (621 kPa); the engine may run or be off but the ignition must be on.
  • Press and release the brake pedal repeatedly to lower pressure and note the gauge reading when the warning activates.
  • Pass: the warning activates at or above 55 psi (380 kPa) on both primary and secondary gauges. Fail: it does not activate, or activates below 55 psi on either gauge.
  • The pressure at which the warning switches off on the way up need not match where it came on.
  • If pressure is too low at the start, the warning comes on as soon as the key is turned on.

Build-up time

  • Close the trailer supply valve if a trailer is attached and lower pressure below 80 psi (552 kPa).
  • With the engine at 600 to 900 rpm, time the rise from 85 psi to 100 psi (587–690 kPa).
  • Pass: two minutes or less. Fail: more than two minutes.

Governor settings

  • Run the engine until pressure stops climbing: that is cut-out (an air dryer purge also signals it).
  • Pump the brakes slowly and note where pressure starts to climb again: that is cut-in, often heard as a change in engine sound.
  • Fail: cut-out above 145 psi (1000 kPa) or cut-in below 80 psi (552 kPa); changes from the manufacturer's range should be reported.
  • Older vehicles may have lower governor settings; operating pressures have risen over the past 20 years.

Air-loss rate

  • Release the spring brakes, establish normal pressure, shut off the engine and hold the pedal fully applied; watch the gauges for one minute after the first drop settles.
  • Maximum loss per minute: straight truck, tractor or bus 3 psi (21 kPa); tractor and trailer 4 psi (28 kPa); tractor with two or more trailers 6 psi (41 kPa).

Tractor protection valve

  • With normal pressure, close (pull out) the trailer supply valve, disconnect the trailer service-line gladhand where you can see it and apply the service brakes.
  • Pass: no air comes out of the service line. Fail: air exhausts from it.
  • If the vehicle may lack an anti-compounding valve, secure it and release the spring brakes before applying the service brakes.

Trailer spring brakes

  • With the trailer fully charged (supply valve pushed in), pull the supply valve out; air should be heard exhausting as the trailer spring brakes apply.
  • Disconnecting the supply line also works but is not recommended while it is under pressure.
  • If unsure, gently apply engine power to confirm the trailer will not move; if the brakes do not apply, they are defective.

Spring brake holding test

  • Apply the spring brakes on the unit being tested, remove the chocks and gently apply engine power in a low gear.
  • The vehicle may rock, but it must not move significantly; preferably test the towing vehicle's spring brakes.

Drain valves

  • Drain the supply tank first until only clean air comes out, then drain the other tanks and confirm every drain valve works.
  • Some moisture from the supply tank is normal; a significant amount from the other tanks is not and must be reported.
  • Any visible oil in the supply tank should be reported or repaired; oil in any other tank risks contaminating the system and must be reported.
  • A sudden increase in moisture or oil from any tank, or a malfunctioning drain valve, must be repaired.

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