On a vehicle equipped with spring parking brakes, what happens if you try to release the parking brake without enough air pressure built up?

Pick an answer

1. The parking brake releases normally regardless of air pressure
2. The parking brake will not release, or will not stay released, until enough air pressure is available to hold the springs back
3. The vehicle will roll forward slightly, then the brake resets on its own
4. The service brakes take over automatically and work at full strength instead, since they don't depend on air pressure like the parking brake does

Correct!

Not quite. The correct answer is highlighted.