What does the low air pressure warning device warn you about?
- The service tank system pressure has fallen too low. ✓
- There is too much moisture in the braking system.
- The governor cut-in pressure is set too low.
- It will soon rain or snow.
Answer: A. The service tank system pressure has fallen too low.
The low air pressure warning device warns you that the service tank system pressure has fallen too low.
Why this is the answer
The truck handbook says this warning operates when pressure drops below the minimum needed for proper brake operation, and it tells you to stop in the safest place and correct the air loss before continuing. A starting check also says the air-pressure gauge must show enough pressure and the audible warning must have stopped before you move. Together, these passages point to a low-pressure warning rather than a moisture, governor setting, or weather signal.
Why the other answers are wrong
- B. There is too much moisture in the braking system. — The passages do not mention moisture in the braking system as the trigger for this warning; they deal with air pressure being too low.
- C. The governor cut-in pressure is set too low. — The passages do not say the warning reports a governor cut-in pressure setting; it reports pressure below what proper brake operation needs.
- D. It will soon rain or snow. — Rain or snow is not connected to the warning in the passages; the warning is about brake air pressure.
Remember it
Treat the low air warning like a stop sign: if it comes on, stop safely and fix the air loss before rolling again.
Official handbook: Official MTO Truck Handbook, Use of brakes