Welcome to your Class A CDL Permit Prep: Combination Vehicles practice quiz.

You should check the back of the fifth wheel to confirm that the jaws have locked around the kingpin.

False

True

None

Where are the shut-off valves located on a combination vehicle?

Inside the trailer air supply control unit on the dashboard

Next to the tractor’s fuel tank near the air compressor

On the landing gear near the frame rail

At the rear of the last trailer in the brake lines

None

What is a correct way to test the trailer's emergency brakes?

Pull out the trailer air supply control and gently pull against the brakes in a low gear

Use the trailer hand valve to apply the brakes while parked

Press the brake pedal and hold it for 60 seconds while monitoring air loss

Apply the parking brake, release the trailer air supply, and turn off the engine

None

What is one way to check that air is flowing to all trailers in a combination vehicle?

Open the emergency line shut-off valve at the rear of the last trailer and listen for air escaping

Pump the foot brake and check for even brake application across all axles

Disconnect the service line and measure the air pressure drop

Release the parking brake and watch for trailer movement

None

What can happen if the trailer is positioned too high when you attempt to couple it to the tractor?

The tractor may back under the trailer without locking the kingpin into the fifth wheel

The air lines may connect improperly and cause a leak

The trailer landing gear could collapse from misalignment

The trailer brakes may automatically release during coupling

None

When pulling a set of trailers, which shut-off valves should be open or closed for proper air flow?

Open at the rear of the first trailer and at the middle of second; closed at the end of the last trailer

Open at the back of every trailer regardless of position

Closed at all trailer connections to prevent air loss

Only the first trailer’s valves should be open; all others should be closed

None

When making a sudden turn while pulling double trailers, which part of the vehicle is most likely to roll over first?

The front trailer axle, because it turns the sharpest

The rear trailer, because it is lighter and more unstable

The tractor, due to its high center of gravity

The lead trailer, because it carries most of the weight

None

Why should you avoid using the trailer hand valve while driving?

Because it puts excess pressure on the front axle brakes

Because it increases fuel consumption at highway speeds

Because it can cause the trailer to skid or jackknife

Because it disables the emergency braking system

None

Why is it necessary to use wheel chocks when parking a trailer that does not have spring brakes?

Because it prevents damage to the trailer’s suspension system

Because the service line automatically engages the brakes when parked

Because air pressure may leak out, causing the brakes to release

Because trailers without spring brakes cannot be steered when disconnected

None

What is the function of the trailer air supply control in a combination vehicle?

It supplies air to the trailer and controls the emergency brakes

It adjusts the suspension height of the trailer during loading

It synchronizes braking pressure between the tractor and trailer

It monitors air pressure in the service line only

None

How can you tell if a trailer is equipped with an antilock braking system (ABS)?

Check the air pressure gauge for a blinking warning light

There is no way to tell without checking underneath the trailer

Feel for brake pulsation when stopping at low speed

Look for a yellow ABS indicator light on the left side of the trailer, near the rear

None

Why is it dangerous to use the trailer hand brake to try to correct a jackknifing trailer?

Because it disconnects the ABS system and causes wheel lock-up

Because it can overheat the tractor brakes and reduce stopping power

Because it may delay braking and cause the load to shift

Because it keeps the trailer wheels locked and makes the skid worse

None

What does the term “off-tracking” refer to when driving a combination vehicle?

When the rear trailer moves ahead of the tractor while turning

When the brakes wear unevenly between tractor and trailer

When the trailer swings out in the opposite direction during a turn

When the trailer follows a tighter path than the tractor during a turn

None

After a proper coupling, how much space should there be between the upper and lower fifth wheel plates?

About one inch of space to allow for trailer movement

Enough space to insert a gloved hand for inspection

A two-inch gap is normal under heavy loads

There should be no visible gap—the plates should be in full contact

None

What is the purpose of the service air line in a combination vehicle?

It supplies air to the trailer suspension and lighting system

It activates the trailer brakes only when the parking brake is applied

It carries air that controls the application of the trailer’s brakes during normal braking

It keeps the trailer’s air tanks pressurized at all times

None

Which of the following trailers is least likely to get stuck on a raised railroad-highway crossing?

Car carrier

Livestock trailer

Flatbed trailer

Lowboy trailer

None

When backing a trailer, you should position the vehicle to back in a curved path toward the driver’s side whenever possible.

False

True

None

How do you test the trailer service brakes to ensure they are working properly?

Press the foot brake while parked and check for trailer movement

Check the air tanks to see if pressure builds during braking

Gently apply the trailer hand valve while moving forward at a slow speed

Pull out the trailer air supply control and release the parking brake

None

What are two key actions a driver can take to help prevent rollover in a combination vehicle?

Take turns slowly and keep the cargo as close to the ground as possible

Drive slowly around turns and keep the cargo centered

Use engine braking on curves and shift to a higher gear

Keep the load low and always use the trailer brakes first

None

Before driving, you should raise the landing gear just enough so it lifts off the ground.

True

False

None

Time's up

Ready to go further? You can take this practice quiz as many times as you need — it’s here to help you feel confident and prepared for your real DMV permit test.

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