Endorsement Practice Questions And

CDL Combination Vehicle (Class A) Endorsement Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the main purpose of the air brakes on a combination vehicle?
• Increase fuel efficiency
• Reduce engine wear
• Provide stopping power for heavy loads
• Maintain vehicle speed

Rationale: Air brakes are designed to stop large, heavy vehicles

safely.

• When coupling a trailer, what is the first step?
• Hook up the electrical lines
• Position the tractor properly and check the trailer height
• Connect the air lines 1 / 4

• Check the tires

Rationale: Proper positioning ensures safe and secure coupling.

• What can happen if the trailer is not properly coupled?
• Faster acceleration
• Trailer can separate from the tractor
• Better fuel efficiency
• Easier steering

Rationale: Improper coupling can lead to dangerous trailer

separation.

• How often should the trailer brakes be tested?
• Once a week
• Before each trip
• Every 1,000 miles
• After loading cargo

Rationale: Pre-trip inspections help ensure brakes function safely.

• What is "trailer swing" or "off-tracking"?
• When a trailer sways in the wind
• When the trailer tires follow a shorter path than the tractor tires

in a turn

• Trailer bouncing on rough roads
• Trailer tire wear

Rationale: Off-tracking occurs due to the length of the trailer relative

to the tractor. 2 / 4

• When inspecting a fifth wheel, what should you check?
• Tire pressure
• Brake wear
• Mounting and locking mechanism
• Engine oil

Rationale: The fifth wheel must be properly locked to secure the

trailer.

• What is the purpose of glad hands on air lines?
• Measure tire pressure
• Connect the tractor and trailer air brake systems
• Signal turns
• Lubricate brakes

Rationale: Glad hands allow air to flow between tractor and trailer

brakes.

• How do you know the trailer is properly coupled to the tractor?
• The trailer tilts
• The fifth wheel release handle moves easily
• The kingpin is locked and the trailer cannot be pulled out
• Air lines are disconnected

Rationale: A properly coupled trailer is securely locked and cannot

separate.

• What is the maximum allowed air pressure in most truck systems?
• 50 psi 3 / 4

• 80 psi
• 90 psi
• 100–120 psi

Rationale: Most air brake systems operate safely between 100–120

psi.

• What is the purpose of a tractor protection valve?
• Protect the engine
• Prevent air loss from the tractor if the trailer breaks away
• Lubricate the trailer
• Control speed

Rationale: The tractor protection valve closes automatically to

protect the tractor’s air supply.

11. When backing a combination vehicle, the trailer tends to:

• Move in the same direction as the steering
• Move in the opposite direction of the steering
• Stay straight
• Swing randomly

Rationale: Trailers pivot on the kingpin, so the rear moves opposite

the steering.

• What is the proper way to brake in a combination vehicle on

slippery roads?

• Brake hard immediately
• Use light, controlled braking to avoid jackknifing
• / 4