In a dual air brake system, if one air system is very low on pressure:

Question

In a dual air brake system, either the front or rear brakes will not be fully operable if one of the air systems gets too low on pressure. If the air pressure in either tank gets too low while you are driving, you should exit the road and park as soon as possible.

Accepted Answer

Either the front or rear brakes will not be fully operable.

Answer

None of the brakes will work at all.

Answer

There is usually no noticeable effect.