Instructions

Combination

All applicants who are applying for a Class A CDL should be prepared to take the Combination test. This test covers information found in Section 6 of the Commercial Driver License.. Read More

All applicants who are applying for a Class A CDL should be prepared to take the Combination test. This test covers information found in Section 6 of the Commercial Driver License Manual. Section 6 provides the information needed to safely operate tractor-trailers, doubles, triples, and straight trucks with trailers. The test is made up of 20 multiple-choice questions, and applicants will need to correctly answer a minimum of 16 questions to pass. The Combination test is not a replacement for the Double/Triple endorsement test.

Number of Question 20

Passing Score 16

15. The emergency air line supplies air to the:

Relay valves.

Trailer air tanks.

Signal line.

The emergency air line (also known as the supply line) has two functions. The first is to supply air to the trailer air tanks, and the second is to control the emergency brakes on combination vehicles.

16. If unsure if a trailer has an Anti-Lock Braking System (ABS), you can:

Look under the trailer for wheel speed sensors coming from the back of the brakes.

Remove a tire and look for the ABS sensor on the axle.

Assume it does have ABS.

If you do not know whether or not a trailer is equipped with ABS, look under the vehicle for the electronic control unit and wheel speed sensor wires coming from the back of the brakes.

17. What is a bobtail tractor?

A tractor without a trailer

A tractor attached to two trailers

A tractor with a tank

Tractors without semi-trailers are referred to as bobtail tractors. Operating a bobtail tractor requires drivers to exercise caution.

18. What is the Johnson bar?

A hand valve that works the trailer brakes

A valve that indicates the fuel level

A valve that limits the amount of cargo

The trailer hand valve, also called the trolley valve or Johnson bar, is used to work the trailer brakes. It should be used only to test the brakes. Using it while a vehicle is in motion could cause a skid.

19. When coupling:

You can assume all vehicles are the same.

Be sure that you are coupling correctly.

Cracks in the mounting are acceptable.

Incorrect coupling and uncoupling of combination vehicles can have extremely dangerous consequences.

20. If you press the tractor air supply control and your trailer's spring brakes do not release, you should:

Inspect the air line connections.

Activate the Anti-Lock Braking System.

Turn the engine off and on again.

It is important that all of a vehicle's equipment is in proper working condition before beginning a trip. If a trailer's spring brakes do not release when you push in the tractor air supply control, you should make sure the air line connections are properly attached and sealed.

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