Michigan CDL - Air Brakes Questions And Answers | Latest 2026
1. A low air pres- When tank pressure falls below 60 psi.
sure warning signal
should activate: In an air brake system, a low air pressure warning signal must come on if air
pressure in the tanks falls below 60 psi. This warning signal may come in the
form of a light, a buzzer, or a wig wag.
2. Why should you reg- Because compressed air contains some water and the water collects in the
ularly drain the air tanks.
tanks?
Compressed air usually contains a certain amount of moisture and compres-
sor oil, which can build up in the air storage tanks and damage the brake
system. The tanks should be drained to clean out these accumulations. On a
tank with a manual drain valve, draining should be performed at the end of
each day of driving.
3. Vehicles equipped Yellow
with Anti-Lock Brak-
ing Systems (ABS) Vehicles with ABS have yellow malfunction lamps to alert drivers when the
have malfunc- braking systems are not working. Be sure you know where the malfunction
tion lamps to indicate lamp on your vehicle is before beginning a trip.
when the ABS is not
working.
4. A dual air brake sys- Consists of two separate air brake systems that share a single set of controls.
tem:
A dual air brake system is made up of two separate air brake systems. The
systems share a single set of brake controls, but each has its own air tanks,
hoses, and lines. One system typically operates the regular brakes on the rear
axle or axles while the other system operates the regular brakes on the front
axle.
5. 150
, Michigan CDL - Air Brakes Questions And Answers | Latest 2026
A safety valve is set to The safety valve protects air tanks and the rest of an air brake system from
open at pounds accumulating too much air pressure. The safety valve is usually set to open at
per square inch (psi). 150 psi.
6. Air pressure should Three minutes.
build up in a single
air system within: In single air systems, air pressure should build from approximately 50 to 90
psi within three minutes.
7. Some air brake sys- To reduce the risk of ice forming in air brake valves.
tems use alcohol:
Some air brake systems contain an alcohol evaporator. This device introduces
alcohol into the braking system to inhibit the formation of ice.
8. Spring brakes come When too much air pressure is lost.
on:
Spring brakes come on automatically when air pressure drops to an unsafe
psi level. Instead of waiting for the spring brakes to automatically activate, you
should safely exit the road as soon as you notice the low pressure warning
signal and bring your vehicle to a stop while you are still able to control the
brakes.
9. On trucks and buses, On the instrument panel
where are ABS mal-
function lamps locat- Tractors, trucks, and buses with Anti-Lock Braking Systems (ABS) have yellow
ed? malfunction lamps located on their instrument panels. Trailers have yellow
ABS malfunction lamps on their left side, either on the front or rear corner.
10. Before driving a ve- 100 psi
hicle with a dual air
brake system, you Before driving a vehicle with a dual air brake system, you should wait for the
must wait for the air air compressor to build up at least 100 psi in both the primary and secondary
compressor to build systems.
a minimum of in
1. A low air pres- When tank pressure falls below 60 psi.
sure warning signal
should activate: In an air brake system, a low air pressure warning signal must come on if air
pressure in the tanks falls below 60 psi. This warning signal may come in the
form of a light, a buzzer, or a wig wag.
2. Why should you reg- Because compressed air contains some water and the water collects in the
ularly drain the air tanks.
tanks?
Compressed air usually contains a certain amount of moisture and compres-
sor oil, which can build up in the air storage tanks and damage the brake
system. The tanks should be drained to clean out these accumulations. On a
tank with a manual drain valve, draining should be performed at the end of
each day of driving.
3. Vehicles equipped Yellow
with Anti-Lock Brak-
ing Systems (ABS) Vehicles with ABS have yellow malfunction lamps to alert drivers when the
have malfunc- braking systems are not working. Be sure you know where the malfunction
tion lamps to indicate lamp on your vehicle is before beginning a trip.
when the ABS is not
working.
4. A dual air brake sys- Consists of two separate air brake systems that share a single set of controls.
tem:
A dual air brake system is made up of two separate air brake systems. The
systems share a single set of brake controls, but each has its own air tanks,
hoses, and lines. One system typically operates the regular brakes on the rear
axle or axles while the other system operates the regular brakes on the front
axle.
5. 150
, Michigan CDL - Air Brakes Questions And Answers | Latest 2026
A safety valve is set to The safety valve protects air tanks and the rest of an air brake system from
open at pounds accumulating too much air pressure. The safety valve is usually set to open at
per square inch (psi). 150 psi.
6. Air pressure should Three minutes.
build up in a single
air system within: In single air systems, air pressure should build from approximately 50 to 90
psi within three minutes.
7. Some air brake sys- To reduce the risk of ice forming in air brake valves.
tems use alcohol:
Some air brake systems contain an alcohol evaporator. This device introduces
alcohol into the braking system to inhibit the formation of ice.
8. Spring brakes come When too much air pressure is lost.
on:
Spring brakes come on automatically when air pressure drops to an unsafe
psi level. Instead of waiting for the spring brakes to automatically activate, you
should safely exit the road as soon as you notice the low pressure warning
signal and bring your vehicle to a stop while you are still able to control the
brakes.
9. On trucks and buses, On the instrument panel
where are ABS mal-
function lamps locat- Tractors, trucks, and buses with Anti-Lock Braking Systems (ABS) have yellow
ed? malfunction lamps located on their instrument panels. Trailers have yellow
ABS malfunction lamps on their left side, either on the front or rear corner.
10. Before driving a ve- 100 psi
hicle with a dual air
brake system, you Before driving a vehicle with a dual air brake system, you should wait for the
must wait for the air air compressor to build up at least 100 psi in both the primary and secondary
compressor to build systems.
a minimum of in
