How should you test your vehicle's low air pressure warning signal?
- Repeatedly press and release the brake pedal to lower the air pressure to 414 kPa (60 psi). ✓
- Pump the brakes while your ignition is off.
- Manually let the air out of your brakes and see if the signal comes on.
- Repeatedly press and release the brake pedal to lower the air pressure to 207 kPa (30 psi).
Answer: A. Repeatedly press and release the brake pedal to lower the air pressure to 414 kPa (60 psi).
To test the low air pressure warning signal, repeatedly press and release the brake pedal to bring the air pressure down to about 414 kPa (60 psi) and watch for the warning to come on.
Why this is the answer
The handbook says the low-air warning device must activate when pressure drops below 60 p.s.i. (414 kPa), and the pre-trip inspection steps tell you to pump the pressure down and check that the warning activates at or above that level. Working the brake pedal is what bleeds the pressure down, so that is how you reach the point where the warning should trigger. Pausing as you go lets you see whether the device comes on at the right pressure.
Why the other answers are wrong
- B. Pump the brakes while your ignition is off. — The passages describe pumping the pressure down with the brakes as part of the running pre-trip check, not doing it with the ignition off, so the warning device would not be tested as described.
- C. Manually let the air out of your brakes and see if the signal comes on. — The handbook method is to pump the pressure down using the brake pedal and watch for the device to activate, not to bleed air out of the system by hand.
- D. Repeatedly press and release the brake pedal to lower the air pressure to 207 kPa (30 psi). — Taking the pressure all the way down to 207 kPa (30 psi) goes well past the 414 kPa (60 psi) point where the warning is supposed to activate, so you would miss the check.
Remember it
Think of 60 psi as the trigger line: pump the pedal down to that number and the warning should already be showing.