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LA CDL Combination practice questions

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Question 1Combination vehicle inspection and coupling/uncoupling

Before backing a tractor-trailer under a trailer to couple, the tractor should be positioned so that the trailer is centered in the mirrors and the trailer apron is roughly how far from the rear of the tractor?

  1. About 10 to 15 feet away
  2. About 12 to 18 inches away Correct answer.
  3. About 50 feet away
  4. Directly touching the fifth wheel

Explanation

A proper starting position places the trailer apron roughly a foot to a foot and a half in front of the tractor so the approach is short and the trailer stays centered in the mirrors. Starting too far away invites misalignment, and starting too close leaves no room to build a straight approach.

Question 2Combination vehicle inspection and coupling/uncoupling

When inspecting the fifth wheel before coupling, which condition should cause you to stop and correct the problem before backing under the trailer?

  1. The fifth wheel is tilted down toward the rear of the tractor Correct answer.
  2. The locking jaws are closed around the kingpin with no gap
  3. The jaws are open and greased
  4. The mounting bolts are tight and the plate is secure

Explanation

An unloaded fifth wheel must be tilted up toward the rear so the trailer apron slides under it and the kingpin can enter the jaws. If the plate is tilted down, the apron will strike it and the coupling cannot complete properly.

Question 3Combination vehicle inspection and coupling/uncoupling

After coupling, you do a pull test. What does a proper pull test consist of?

  1. Release the parking brake and drive forward at highway speed
  2. Raise the landing gear and lower the trailer apron
  3. Release both tractor and trailer brakes and roll backward
  4. Set the trailer brakes, put the tractor in a low gear, and gently pull forward Correct answer.

Explanation

The pull test confirms the kingpin is locked in the jaws: with the trailer brakes set and the tractor in a low gear, a gentle forward pull should meet firm resistance without the trailer moving. If the tractor moves freely, the coupling is not secure.

Question 4Combination vehicle inspection and coupling/uncoupling

You have backed under the trailer and the kingpin is locked. What is the correct sequence for the remaining coupling steps?

  1. Pull test, raise landing gear, connect air lines, then release the tractor parking brake
  2. Secure the trailer, connect air lines, pull test, then raise landing gear Correct answer.
  3. Connect air lines, secure the trailer, raise landing gear, then pull test
  4. Raise landing gear, connect air lines, secure the trailer, then pull test

Explanation

After the kingpin locks, you secure the tractor against rolling, connect the air lines and check that trailer brakes release and set, complete the pull test, and only then raise the landing gear. Raising the gear before a successful pull test risks dropping the trailer.

Question 5Combination vehicle inspection and coupling/uncoupling

While raising the landing gear after a successful coupling, you notice the crank turns with almost no resistance and the trailer does not seem to lift. What is the most likely explanation?

  1. The air lines are connected backward
  2. The landing gear is fully raised and the crank is freewheeling
  3. The kingpin is not locked in the jaws
  4. The trailer is still resting on the fifth wheel and the gear is not supporting weight Correct answer.

Explanation

Once the trailer weight rests on the fifth wheel, the landing gear carries no load, so the crank turns easily. That easy turning is normal after coupling; it is not a sign of a fault by itself.

Question 6Combination vehicle inspection and coupling/uncoupling

When connecting the air lines between tractor and trailer, which color line supplies air to the trailer's emergency (supply) system and must be connected so the trailer brakes release?

  1. Blue
  2. Green
  3. Yellow
  4. Red Correct answer.

Explanation

The red line is the emergency or supply line that charges the trailer system; when it is connected and charged, the trailer brakes release. The blue line is the service line that delivers brake application pressure.

Question 7Combination vehicle inspection and coupling/uncoupling

After connecting the air lines and charging the system, you perform a trailer brake check. What should happen when you apply the trailer hand valve or push the tractor brake pedal?

  1. The trailer brakes should apply and the tractor should resist forward movement Correct answer.
  2. Only the tractor brakes should apply
  3. The trailer brakes should stay released while the tractor moves
  4. The trailer brakes should apply only after the parking brake is released

Explanation

A correct brake check confirms the trailer brakes respond to the control: they should apply and hold the trailer, and the tractor should feel resistance if you try to move. If the trailer does not brake, the lines are crossed or not fully connected.

Question 8Combination vehicle inspection and coupling/uncoupling

During the walk-around inspection of a combination vehicle, you check the coupling by looking at the fifth wheel from the side. What confirms a proper connection?

  1. The locking jaws are visible closed around the kingpin with no gap Correct answer.
  2. The trailer apron is resting on top of the fifth wheel plate
  3. The landing gear is still on the ground
  4. The air lines hang loose below the fifth wheel

Explanation

Looking under the trailer, you should see the jaws closed around the kingpin with no gap, and the release handle should be in the locked position. A visible gap or an open handle means the coupling is not secure.

Question 9Combination vehicle inspection and coupling/uncoupling

You are preparing to uncouple. Which step should be completed to support the trailer before you release the fifth wheel locking jaws?

  1. Disconnect the air lines and electrical cord
  2. Release the tractor parking brake
  3. Lower the landing gear until it touches the ground and bears the trailer weight Correct answer.
  4. Pull the tractor forward slightly

Explanation

The landing gear must be lowered and firm on the ground before the jaws are released so the trailer is supported when the tractor pulls away. Disconnecting the lines also occurs before unlocking, but it does not physically support the trailer.

Question 10Combination vehicle inspection and coupling/uncoupling

When uncoupling, why should you pull the tractor forward slowly and only a short distance after releasing the jaws?

  1. To clear the kingpin without dragging the trailer or damaging the apron Correct answer.
  2. To recharge the trailer air tanks
  3. To keep the trailer from rolling forward
  4. To set the trailer spring brakes

Explanation

A short, slow pull clears the kingpin from the jaws and lets the trailer settle onto its landing gear without dragging or bending the apron. Pulling too fast or too far can damage the trailer or the tractor.

Question 11Combination vehicle inspection and coupling/uncoupling

You are uncoupling on a slight slope. What is the safest practice for the trailer before you release the fifth wheel?

  1. Lower the landing gear only after pulling away
  2. Chock the trailer wheels and set the trailer parking brakes Correct answer.
  3. Rely on the tractor parking brake alone
  4. Leave the trailer brakes released so it can settle

Explanation

On any slope, the trailer must be held by its own parking brakes and chocks before the tractor is removed. Otherwise the trailer can roll once the tractor no longer holds it.

Question 12Combination vehicle inspection and coupling/uncoupling

Which item on the tractor should you inspect for cracks or looseness because a failure there can let the fifth wheel separate from the tractor?

  1. The exhaust stack brackets
  2. The air dryer cartridge
  3. The mud flaps
  4. The fifth wheel mounting bolts and frame Correct answer.

Explanation

The fifth wheel is bolted to the tractor frame, and cracked or loose mounting bolts can allow the plate to shift or separate under load. This is a critical coupling inspection item.

Question 13Combination vehicle inspection and coupling/uncoupling

While inspecting the kingpin area, you find the kingpin is bent. What is the correct action?

  1. Use a smaller fifth wheel plate to fit the bend
  2. Grease the kingpin heavily to compensate
  3. Couple as normal and monitor it during the trip
  4. Do not couple; report the defect and have the trailer repaired Correct answer.

Explanation

A bent kingpin cannot seat properly in the jaws and may not lock, so the trailer must be taken out of service until repaired. Coupling to a defective kingpin risks separation on the road.

Question 14Combination vehicle inspection and coupling/uncoupling

When checking the gap between the tractor and trailer after coupling, you find a large gap at the top of the fifth wheel. What does this most likely indicate?

  1. The landing gear is too high
  2. The trailer is not fully seated on the fifth wheel Correct answer.
  3. The coupling is correct and the gap is normal
  4. The air lines are reversed

Explanation

A visible gap between the trailer apron and the fifth wheel plate means the trailer is riding high and not fully seated, often because the jaws did not close or the plate was tilted the wrong way. The coupling must be redone before driving.

Question 15Combination vehicle inspection and coupling/uncoupling

You are inspecting the air lines and find a cut in the red line's outer jacket that exposes the reinforcement but does not reach the inner tube. What is the appropriate action?

  1. Ignore it because the inner tube is intact
  2. Shorten the line by cutting off the damaged section
  3. Report and replace the line as a defect Correct answer.
  4. Tape the cut and continue the trip

Explanation

Any cut that exposes the reinforcement weakens the line and can lead to a burst under pressure, so it must be reported and the line replaced. Field repairs like taping or trimming do not restore the line's integrity.

Question 16Combination vehicle inspection and coupling/uncoupling

During the pre-trip inspection of a combination vehicle, you check the electrical cord. Which condition indicates the cord needs attention?

  1. The cord has slack and is secured with a spring hanger
  2. The cord is fully seated in the receptacle with the locking tab engaged
  3. The cord is clean and dry
  4. The cord has exposed wires and the insulation is cracked Correct answer.

Explanation

Cracked insulation or exposed wires on the electrical cord can cause short circuits and loss of trailer lights, so the cord must be repaired or replaced. A properly seated, secured, clean cord is the correct condition.

Question 17Combination vehicle inspection and coupling/uncoupling

You are coupling to a trailer and notice the trailer's spring brakes are released and the wheels are not chocked. What should you do before backing under?

  1. Have someone hold the trailer
  2. Back under quickly before the trailer moves
  3. Connect the air lines first to charge the system
  4. Set the trailer parking brakes and chock the wheels Correct answer.

Explanation

A trailer that is not held by its brakes or chocks can roll during coupling, so it must be secured first. Once the trailer is stable, you can complete the coupling safely.

Question 18Combination vehicle inspection and coupling/uncoupling

When inspecting the fifth wheel, you notice the jaws are closed but the release handle is pulled out. What does this mean?

  1. The kingpin is greased
  2. The trailer brakes are set
  3. The jaws are not locked and the coupling is unsafe Correct answer.
  4. The coupling is locked and ready to drive

Explanation

The release handle must be pushed in for the jaws to stay locked; a pulled-out handle means the lock is not engaged and the trailer can separate. The coupling must be corrected before driving.

Question 19Combination vehicle inspection and coupling/uncoupling

What is the purpose of the trailer apron (the plate under the trailer nose)?

  1. To guide the kingpin into the fifth wheel jaws and protect the trailer nose Correct answer.
  2. To connect the electrical cord
  3. To support the trailer when uncoupled
  4. To hold the trailer brakes in the released position

Explanation

The apron is the flat surface that rides on the fifth wheel plate and guides the kingpin into the jaws as you back under. It also protects the trailer nose from damage during coupling.

Question 20Combination vehicle inspection and coupling/uncoupling

After uncoupling, you notice the trailer nose is resting too low and the landing gear is not touching the ground. What is the most likely cause?

  1. The fifth wheel was greased
  2. The trailer brakes were set
  3. The landing gear was not lowered before releasing the jaws Correct answer.
  4. The air lines were disconnected

Explanation

If the landing gear is not on the ground when the tractor pulls away, the trailer nose drops onto the frame or ground. The gear must be lowered and firm before the jaws are released.

Question 21Combination vehicle inspection and coupling/uncoupling

During a pre-trip inspection, you check the slack adjusters on the trailer. What should you look for?

  1. That the slack adjuster is painted the same color as the tractor
  2. That the adjuster is disconnected from the brake chamber
  3. That the push rod is fully extended at rest
  4. That the push rod travel is within the allowed limit and the adjuster is not damaged Correct answer.

Explanation

Slack adjusters transfer force from the brake chamber to the brake, and excessive push rod travel or damage means the brakes may not apply fully. The inspection checks travel limits and condition.

Question 22Combination vehicle inspection and coupling/uncoupling

You are doing the walk-around and notice the trailer's air line gladhands are not sealed and air is escaping at the connection. What should you do?

  1. Check that the gladhand seals are in place and the couplers are fully engaged Correct answer.
  2. Disconnect the line and drive without it
  3. Increase engine RPM to overcome the leak
  4. Continue because a small leak is normal

Explanation

Air escaping at the gladhand means the seal is missing, damaged, or the couplers are not fully engaged, and the system will not hold pressure. The connection must be corrected before driving.

Question 23Combination vehicle inspection and coupling/uncoupling

What is the correct order for the pre-trip inspection of a combination vehicle?

  1. Start at the fifth wheel and work outward in both directions
  2. Start at the rear of the trailer and work forward
  3. Start at the front of the tractor and work back to the rear of the trailer Correct answer.
  4. Start at the trailer and work forward to the tractor

Explanation

A systematic walk-around begins at the front of the tractor and proceeds to the rear of the trailer so no item is skipped. A consistent order makes it easier to catch defects and repeat the inspection the same way each time.

Question 24Combination vehicle inspection and coupling/uncoupling

You are inspecting the trailer frame and find a crack in a crossmember. What is the correct action?

  1. Weld it yourself before the trip
  2. Note it and continue because crossmembers are not structural
  3. Report the defect and do not use the trailer until repaired Correct answer.
  4. Load the trailer lightly to reduce stress

Explanation

A cracked crossmember weakens the trailer frame and can lead to structural failure under load, so it must be reported and repaired before use. Field welding by the driver is not an acceptable repair.

Question 25Combination vehicle inspection and coupling/uncoupling

When coupling at night, what is the best practice for aligning the tractor with the trailer?

  1. Use the trailer lights alone to judge alignment
  2. Rely on the backup alarm to judge distance
  3. Back quickly to reduce the time exposed to traffic
  4. Use the mirrors and a spotter or adequate lighting to keep the trailer centered Correct answer.

Explanation

At night, good lighting and a spotter or careful mirror use are needed to keep the trailer centered and judge distance. Rushing or relying on sound does not give reliable alignment.

Question 26Combination vehicle inspection and coupling/uncoupling

Before backing under a trailer to couple, what is the proper height for the trailer nose?

  1. High enough that the trailer apron clears the fifth wheel and the kingpin sits just above the jaws Correct answer.
  2. Low enough that the trailer apron touches the top of the fifth wheel for alignment
  3. As low as the landing gear allows so the tractor can lift the trailer
  4. Level with the tractor frame so the kingpin slides in horizontally

Explanation

The trailer should be raised so the apron clears the fifth wheel and the kingpin rides just above the jaws, allowing the fifth wheel to scoop under and lock. If the trailer is too low the tractor may strike the nose; if too high the kingpin can pass over the fifth wheel.

Question 27Combination vehicle inspection and coupling/uncoupling

When you back the tractor under a trailer during coupling, how should you move the tractor?

  1. Back with the trailer brakes released so the trailer rolls backward
  2. Back slowly with the tractor aligned straight to the trailer Correct answer.
  3. Back steadily and fast so the kingpin snaps into the jaws
  4. Back at an angle so the fifth wheel guides the kingpin in

Explanation

Backing slowly and straight lets the fifth wheel enter the trailer apron squarely and the kingpin engage the jaws without damage. Fast or angled backing can bend the kingpin, crack the apron, or push the trailer out of position.

Question 28Combination vehicle inspection and coupling/uncoupling

After the fifth wheel jaws close on the kingpin, what is the correct next step before you finish coupling?

  1. Pull the release handle out to confirm the jaws are free
  2. Release the tractor parking brake and drive forward to test the coupling
  3. Connect the electrical cord before any air lines
  4. Do a pull test with the trailer brakes locked Correct answer.

Explanation

A pull test confirms the jaws are locked: with the trailer brakes set, pull gently against them and the tractor should not move. This verifies the coupling before you rely on it on the road.

Question 29Combination vehicle inspection and coupling/uncoupling

Which color air line supplies air to the trailer's emergency (supply) system?

  1. Black
  2. Red Correct answer.
  3. Green
  4. Blue

Explanation

The red line is the emergency or supply line, and the blue line is the service line. The green and black lines do not exist on a standard tractor-trailer air system.

Question 30Combination vehicle inspection and coupling/uncoupling

When coupling, the trailer's spring brakes should be in what condition?

  1. Set only after the air lines are connected
  2. Set so the trailer cannot roll during coupling Correct answer.
  3. Released so the trailer can roll into alignment
  4. Released only after the kingpin is engaged

Explanation

The trailer spring brakes must be set, and the wheels chocked if possible, so the trailer stays put while the tractor backs under it. A trailer that rolls during coupling can cause injury or damage.

Question 31Combination vehicle inspection and coupling/uncoupling

What does the trailer apron do during coupling?

  1. It supports the trailer when the landing gear is raised
  2. It holds the kingpin in place once the jaws close
  3. It seals the air lines at the gladhands
  4. It guides the fifth wheel under the trailer and protects the nose from damage Correct answer.

Explanation

The apron is the plate under the trailer nose that the fifth wheel slides against, guiding the coupling and spreading the load. It also helps prevent the tractor from striking and damaging the trailer nose.

Question 32Combination vehicle inspection and coupling/uncoupling

During the walk-around inspection, what should you check on the fifth wheel?

  1. That the fifth wheel is greased only on the top surface
  2. That the jaws are open and the handle is pulled out
  3. That the fifth wheel is tilted down toward the rear
  4. That the jaws are closed and the release handle is pushed in Correct answer.

Explanation

With the trailer coupled, the jaws should be closed around the kingpin and the release handle pushed fully in. An open jaw or a handle pulled out means the coupling is not secure.

Question 33Combination vehicle inspection and coupling/uncoupling

Why should the landing gear be fully raised before you drive away after coupling?

  1. It reduces the weight on the fifth wheel
  2. It prevents the landing gear from striking the ground or road debris Correct answer.
  3. It helps the trailer brakes apply more evenly
  4. It keeps the trailer level on the road

Explanation

Landing gear left down can catch on the ground, railroad tracks, or debris and be damaged or cause a loss of control. It must be cranked fully up before moving.

Question 34Combination vehicle inspection and coupling/uncoupling

You are coupling to a trailer and the kingpin sits too high to enter the jaws. What is the correct action?

  1. Back harder so the fifth wheel forces the trailer up
  2. Pull forward and approach at an angle to catch the kingpin
  3. Lower the landing gear until the trailer nose drops onto the fifth wheel
  4. Raise the trailer with the landing gear until the kingpin is just above the jaws Correct answer.

Explanation

If the kingpin is too high it will ride over the fifth wheel instead of locking, so the trailer must be lowered or raised as needed until the kingpin sits just above the jaws. Forcing the tractor can damage the fifth wheel, apron, or kingpin.

Question 35Combination vehicle inspection and coupling/uncoupling

During a pull test, the tractor moves backward slightly and then stops while the trailer brakes are set. What does this indicate?

  1. The trailer brakes are not holding and need adjustment
  2. The coupling is secure and the trailer is holding the tractor Correct answer.
  3. The fifth wheel jaws are open and the kingpin slipped out
  4. The tractor parking brake is dragging

Explanation

A small amount of movement before the rig stops is normal slack being taken up, and the trailer brakes then hold the tractor. This confirms the jaws are locked and the trailer brakes are working.

Question 36Combination vehicle inspection and coupling/uncoupling

After connecting the air lines, you hear a steady hiss at a gladhand. What should you do?

  1. Continue the inspection and note it at the next stop
  2. Disconnect the red line and drive with the blue line only
  3. Check the gladhand seals and couplers, then reconnect until the leak stops Correct answer.
  4. Increase engine rpm to overcome the leak

Explanation

A steady hiss at a gladhand usually means a bad seal, a loose coupler, or a misaligned connection. The lines must be reseated or the seals replaced until the leak stops before the vehicle is driven.

Question 37Combination vehicle inspection and coupling/uncoupling

You are inspecting the electrical cord and find the plug is loose in the socket. What is the correct action?

  1. Tape the plug in place and continue
  2. Coat the plug with grease to hold it
  3. Push the plug in firmly and confirm it locks, replacing it if it will not Correct answer.
  4. Leave it loose because the cord is only for clearance lights

Explanation

A loose plug can vibrate out and cause loss of lights or antilock brake power. It must seat and lock securely, and a plug that will not stay should be replaced.

Question 38Combination vehicle inspection and coupling/uncoupling

When uncoupling, which step comes first?

  1. Pull the tractor forward slightly
  2. Disconnect the air lines and electrical cord
  3. Release the fifth wheel locking jaws
  4. Lower the landing gear to the ground Correct answer.

Explanation

Lowering the landing gear first supports the trailer before any connection is released. Only after the trailer is supported should you disconnect the lines and then release the jaws.

Question 39Combination vehicle inspection and coupling/uncoupling

After you release the fifth wheel jaws during uncoupling, how should you move the tractor?

  1. Pull forward slowly a short distance, then stop and check Correct answer.
  2. Turn sharply to swing the tractor clear
  3. Pull forward quickly to clear the trailer
  4. Back up to clear the kingpin

Explanation

Pulling forward slowly and only a short distance lets you confirm the trailer is stable on its landing gear before moving further. A fast or sharp move can damage the trailer or cause it to tip.

Question 40Combination vehicle inspection and coupling/uncoupling

You are coupling and notice the trailer is not quite aligned with the tractor. What is the safest approach?

  1. Have someone push the trailer nose into line while you back
  2. Back faster so the kingpin centers itself
  3. Pull forward, realign the tractor squarely with the trailer, and back again Correct answer.
  4. Back at an angle and let the fifth wheel straighten the trailer

Explanation

The tractor should be pulled forward and realigned so the approach is straight and square. Backing at an angle or forcing alignment can bend the kingpin, crack the apron, or damage the fifth wheel.

Question 41Combination vehicle inspection and coupling/uncoupling

During the pre-trip inspection, what should you check on the trailer's air lines?

  1. That they are properly connected, not cut or chafed, and not leaking Correct answer.
  2. That they are routed over the top of the trailer frame
  3. That they are disconnected so air can flow freely
  4. That they are the same length and color

Explanation

Air lines must be properly connected with good seals, free of cuts and chafing, and not leaking. Damaged or leaking lines can cause brake failure or a trailer brake lockup.

Question 42Combination vehicle inspection and coupling/uncoupling

You are inspecting the trailer and find the landing gear crank handle is missing. What is the correct action?

  1. Report it and have the handle replaced before the trailer is used Correct answer.
  2. Lower the landing gear and leave it down
  3. Ignore it because the landing gear is raised
  4. Use a pair of pliers to crank the gear when needed

Explanation

A missing crank handle means the landing gear cannot be lowered safely when the trailer is uncoupled. It must be replaced before the trailer is used so the trailer can be supported properly.

Question 43Combination vehicle inspection and coupling/uncoupling

When inspecting the tractor's fifth wheel mounting, what should you look for?

  1. The height of the tractor frame above the tires
  2. The color of the release handle
  3. Grease only on the jaws
  4. Loose or missing mounting bolts and cracks in the frame or bracket Correct answer.

Explanation

The fifth wheel is held to the tractor frame by mounting bolts and brackets, and loose or missing bolts or cracks can let the fifth wheel separate from the tractor. This is a critical safety check.

Question 44Combination vehicle inspection and coupling/uncoupling

After coupling and connecting the lines, you charge the trailer air system. What should you do next?

  1. Perform a trailer brake check to confirm the brakes apply and release Correct answer.
  2. Disconnect the red line to test the emergency system
  3. Lower the landing gear to the ground
  4. Drive away immediately to save time

Explanation

After the system is charged, a trailer brake check confirms the service and emergency brakes apply and release correctly. Driving away without this check risks a trailer with faulty brakes.

Question 45Combination vehicle inspection and coupling/uncoupling

You are uncoupling on level ground and the trailer is loaded. What should you do before releasing the fifth wheel jaws?

  1. Lower the landing gear until it firmly contacts the ground Correct answer.
  2. Chock the tractor wheels only
  3. Raise the landing gear fully
  4. Disconnect the electrical cord last

Explanation

The landing gear must be lowered until it firmly contacts the ground so it carries the trailer's weight before the jaws are released. Otherwise the trailer nose will drop when the tractor pulls away.

Question 46Combination vehicle inspection and coupling/uncoupling

During a walk-around, you notice the trailer's spring brake chambers are not building air pressure. What is the most likely consequence?

  1. The fifth wheel jaws will not lock
  2. The trailer lights will not work
  3. The trailer spring brakes will stay applied and the wheels will not roll Correct answer.
  4. The trailer service brakes will apply too strongly

Explanation

Spring brakes are held applied by springs and released by air pressure. Without air pressure to the trailer, the spring brakes stay applied and the trailer wheels will not roll.

Question 47Combination vehicle inspection and coupling/uncoupling

You are coupling at night and cannot clearly see the kingpin and jaws. What is the best practice?

  1. Have someone stand behind the trailer and shout when close
  2. Use a flashlight to check the coupling and the gap after backing under Correct answer.
  3. Back quickly so less time is spent in the dark
  4. Rely on the sound of the jaws closing

Explanation

At night you need a flashlight to confirm the jaws are closed, the handle is in, and the gap between the tractor and trailer is correct. Sound alone does not confirm a secure coupling.

Question 48Combination vehicle inspection and coupling/uncoupling

After coupling, you see a gap between the top of the fifth wheel and the trailer apron. What does this most likely mean?

  1. The electrical cord is disconnected
  2. The kingpin is not fully seated in the jaws or the trailer is too high Correct answer.
  3. The coupling is normal and the gap is expected
  4. The trailer brakes are set

Explanation

A gap at the top of the fifth wheel suggests the kingpin is not fully seated or the trailer is riding too high. This should be corrected before driving because the coupling may not be secure.

Question 49Combination vehicle inspection and coupling/uncoupling

You are inspecting a combination vehicle and find a cut in the red air line's outer jacket that exposes the reinforcement but does not leak. What is the correct action?

  1. Wrap it with tape and continue the trip
  2. Replace the line before the vehicle is used Correct answer.
  3. Switch the red and blue lines to balance the wear
  4. Ignore it because the line is not leaking

Explanation

A cut that exposes the reinforcement weakens the line and can fail under pressure or vibration, even if it is not leaking now. The line should be replaced before the vehicle is used.

Question 50Combination vehicle inspection and coupling/uncoupling

During uncoupling, you release the jaws and the trailer nose starts to drop. What is the most likely cause?

  1. The landing gear was not lowered to the ground Correct answer.
  2. The trailer brakes were set
  3. The fifth wheel was greased
  4. The electrical cord was still connected

Explanation

If the landing gear was not down and in contact with the ground, nothing supports the trailer once the jaws release, so the nose drops. The landing gear must carry the weight before uncoupling.