Air and Electrical Lines - ONLINE CDL SCHOOL

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Air and Electrical Lines

Build confidence with 10 original questions about Air and Electrical Lines. Review your answers and explanations after finishing.

Supplemental study practice. This is not a government licensing exam or ELDT certification, and does not replace hands-on training. Follow your state’s current handbook.

1 / 10

If you accidentally cross the service and emergency air lines when coupling, what is a likely result?

The trailer brakes will lock up immediately

The landing gear will not retract

The electrical system will short out

The trailer spring brakes will not release when you push the trailer air supply control

2 / 10

You are preparing to check that air flows to all trailers in a double trailer setup. What should you do at the rear of the last trailer?

Turn off the engine

Open the emergency line shut-off valve and listen for air escaping

Disconnect the service line

Release the landing gear

3 / 10

While driving, you notice the trailer emergency brakes have activated. What could cause this?

A loss of air pressure in the emergency line

The trailer hand valve being used for parking

The electrical cord being unplugged

The landing gear not being fully raised

4 / 10

During a brake check, how do you test the trailer service brakes using the hand control?

Release the service brakes and coast

Move forward slowly and apply the trailer brakes with the hand valve

Pull out the trailer air supply knob while stopped

Apply the parking brake and step on the accelerator

5 / 10

After connecting the emergency and service air lines during coupling, how should you check that air is reaching the trailer’s brake system?

Pull out the parking brake and step on the accelerator

Push in the trailer air supply knob and listen for air movement at the trailer brakes

Turn on the headlights and check for a warning light

Release the landing gear and watch for trailer movement

6 / 10

After disconnecting a trailer, what should you do with the air lines if dummy couplers are available?

Store the hoses inside the cab

Attach the hoses to the dummy couplers to keep out dirt and water

Connect the hoses together

Leave the hoses hanging loose

7 / 10

You are parking a trailer without spring brakes. What must you do before leaving the trailer unattended?

Disconnect the air lines

Release the trailer brakes

Lower the landing gear only halfway

Chock the wheels to prevent movement

8 / 10

You are inspecting a combination vehicle. Which shut-off valves should be closed?

None of the shut-off valves

The ones at the front of the first trailer

Only the ones at the back of the last trailer

All shut-off valves on every trailer

9 / 10

You are preparing to connect air lines during coupling. What is the correct way to connect the glad hands?

Press the seals together at a 90-degree angle and twist to lock

Push them straight together without twisting

Connect the blue to the red line for extra security

Insert a pin through both couplers

10 / 10

During a pre-trip inspection, you notice water in the trailer air tanks. What should you do?

Only drain the tanks once a week

Ignore it if the brakes seem to work

Drain each air tank to remove moisture

Add more air pressure to clear the water

Your score is

The average score is 0%

About the Air and Electrical Lines practice quiz

This practice quiz focuses on Air and Electrical Lines, listed under CDL Practice — Combination Vehicles. Use it to check what you understand, spot topics to revisit, and connect the material to safe, informed decisions on the road.

Before you begin

Keep your current CDL manual or course notes nearby. Read each prompt carefully and think through why an answer fits, especially when a question describes a vehicle, road, or workplace situation. Licensing rules and procedures can vary, so confirm requirements with current official materials for your state.

After you finish

Review any explanations shown with your results. Note unfamiliar terms or missed concepts, then revisit your manual or course notes before trying again. Use your score to guide study; understanding why an answer is correct matters more than the number alone.

Study note: These quizzes are independent study practice. They are not state licensing exams, official government materials, or ELDT certification, and they do not replace required training.

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