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NJ CDL Combination study materials
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NJ CDL Combination practice questions

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Question 1Combination vehicle inspection and coupling/uncoupling

Before backing a tractor-trailer under a kingpin, the trailer landing gear should be raised so the trailer apron is at what position relative to the fifth wheel?

  1. Slightly higher than the fifth wheel so the tractor can back under without striking the apron Correct answer.
  2. Slightly lower than the fifth wheel so the trailer must be lifted onto it
  3. Level with the fifth wheel so the kingpin slides straight in
  4. Fully retracted with the trailer resting on the ground

Explanation

The trailer should be positioned so its front is slightly higher than the fifth wheel; this lets the tractor back under the trailer without the frame or apron hitting the fifth wheel or the tractor's frame. Raising the landing gear a bit above the fifth wheel height gives the clearance needed for the coupling to occur cleanly.

Question 2Combination vehicle inspection and coupling/uncoupling

You have backed under the trailer and the fifth wheel jaws have closed around the kingpin. What is the correct next action before you begin the pull test?

  1. Release the trailer parking brake and drive forward slowly
  2. Shut off the engine and check the jaws by hand
  3. Raise the landing gear fully to the travel position
  4. Set the tractor parking brake and tug gently forward against the locked trailer brakes Correct answer.

Explanation

After coupling, the standard sequence is to set the parking brake, then pull forward gently with the trailer brakes still locked to confirm the kingpin is captured. This pull test verifies the jaws are actually closed before you trust the connection. Raising the landing gear or releasing brakes comes only after the pull test succeeds.

Question 3Combination vehicle inspection and coupling/uncoupling

During a coupling inspection, which condition indicates the fifth wheel jaws have properly engaged the kingpin?

  1. The jaws are closed around the kingpin and the release handle is pushed in with the latch engaged Correct answer.
  2. The release handle is pulled out and the safety latch is open
  3. The release handle has fallen free of its slot
  4. The jaws are partially open but the kingpin is visible in the throat

Explanation

Proper engagement means the jaws are fully closed around the kingpin and the release (locking) handle is in, with its safety latch secured. The handle position and latch are the visible confirmation that the locking mechanism is seated. An open handle or open latch means the coupling is not secure.

Question 4Combination vehicle inspection and coupling/uncoupling

When should the trailer air supply (emergency) line be connected during coupling?

  1. After the electrical cord, so the trailer lights are working when air is applied Correct answer.
  2. Only after the pull test is completed
  3. Before backing under the trailer, so the brakes are charged during coupling
  4. Before the electrical cord, so the trailer brakes release first

Explanation

The electrical cord is connected first, followed by the air supply line. Connecting electricity first ensures the trailer lights function before air is supplied, and it avoids the risk of the cord being dragged or damaged. The air line charges the trailer system and releases the spring brakes once pressure builds.

Question 5Combination vehicle inspection and coupling/uncoupling

After connecting the air lines, you hear a steady hiss at the gladhand couplers. What does this most likely indicate?

  1. A leak at the coupler seals that must be corrected before driving Correct answer.
  2. Normal operation, because gladhands always leak slightly
  3. The trailer spring brakes are releasing as designed
  4. The tractor protection valve has closed correctly

Explanation

A continuous hiss at the gladhands indicates a leak at the coupler seals, which will bleed air pressure and can prevent the trailer brakes from releasing properly or cause a low-pressure warning. Leaking couplers should be reseated or repaired before the vehicle is driven. Gladhands should seal tightly with no audible leak.

Question 6Combination vehicle inspection and coupling/uncoupling

When uncoupling a trailer, why should you lower the landing gear until it touches the ground before releasing the fifth wheel?

  1. To lock the fifth wheel jaws open
  2. To charge the trailer air tanks
  3. To keep the trailer from dropping and damaging the landing gear or frame when the tractor pulls out Correct answer.
  4. To raise the trailer nose above the fifth wheel height

Explanation

Lowering the landing gear to firm ground contact supports the trailer's weight before the fifth wheel is released. If the gear is not down, the trailer nose will drop when the tractor pulls away, damaging the landing gear, frame, or kingpin area. The gear must be firmly on the ground, not hovering.

Question 7Combination vehicle inspection and coupling/uncoupling

What is the purpose of the safety latch on the fifth wheel release handle?

  1. It holds the air lines clear of the fifth wheel
  2. It prevents the release handle from moving and opening the jaws while driving Correct answer.
  3. It locks the trailer landing gear in the raised position
  4. It secures the electrical cord to the tractor

Explanation

The safety latch keeps the release handle from being bumped or vibrating open, which would let the jaws release and the trailer separate from the tractor. It is a secondary lock on the coupling mechanism. The latch must be engaged after every coupling.

Question 8Combination vehicle inspection and coupling/uncoupling

During a pre-trip inspection of a combination vehicle, you check the trailer's spring brakes by pulling the trailer air supply valve. What should happen?

  1. The tractor brakes release while the trailer stays set
  2. The trailer brakes release and the wheels turn freely
  3. The trailer brakes set and the trailer cannot be moved Correct answer.
  4. Nothing changes because the tractor protection valve blocks the signal

Explanation

Closing the trailer air supply valve (pulling the red knob) removes air pressure and causes the trailer spring brakes to apply. With the trailer brakes set, an attempted gentle pull should not move the trailer. This confirms the trailer emergency braking system works.

Question 9Combination vehicle inspection and coupling/uncoupling

You are inspecting the coupling and notice the trailer apron is resting on the tractor frame rather than on the fifth wheel. What is the correct interpretation?

  1. This is normal and indicates a secure coupling
  2. The kingpin is fully seated and the jaws are locked
  3. The landing gear is correctly supporting the trailer
  4. The trailer is riding too low and the fifth wheel is not carrying the load properly Correct answer.

Explanation

The trailer's weight should be carried by the fifth wheel plate, not by the tractor frame. If the apron rests on the frame, the trailer is too low relative to the fifth wheel, which can damage components and indicates improper coupling height. The coupling should be corrected before driving.

Question 10Combination vehicle inspection and coupling/uncoupling

When sliding the tractor's fifth wheel to adjust weight distribution, what must be done first?

  1. Release the trailer brakes and drive forward slowly
  2. Secure the trailer with its brakes and lower the landing gear to support it Correct answer.
  3. Raise the fifth wheel release handle and pull forward
  4. Disconnect the air lines from the trailer

Explanation

Before sliding the fifth wheel, the trailer must be supported independently: set the trailer brakes and lower the landing gear so the trailer does not move or drop when the fifth wheel is unlocked. Only then can the locking mechanism be released and the tractor moved to reposition the fifth wheel.

Question 11Combination vehicle inspection and coupling/uncoupling

Which item is checked on the trailer during the walk-around portion of a combination vehicle inspection?

  1. The trailer's frame, cross members, and landing gear Correct answer.
  2. The tractor's steering wheel free play
  3. The tractor's engine oil level
  4. The tractor's horn operation

Explanation

The trailer walk-around covers trailer-specific components such as the frame, cross members, landing gear, suspension, and body. Tractor engine, steering, and horn checks belong to the tractor inspection, not the trailer portion. Keeping the two areas separate helps ensure nothing is missed.

Question 12Combination vehicle inspection and coupling/uncoupling

What does the tractor protection valve do when air pressure in the tractor system drops below a safe level?

  1. It disconnects the electrical cord
  2. It releases the trailer brakes to allow a safe stop
  3. It increases pressure to the trailer to compensate
  4. It closes to keep air from escaping the tractor and applies the trailer brakes Correct answer.

Explanation

The tractor protection valve closes when tractor air pressure falls too low, preventing air loss from the tractor and causing the trailer spring brakes to apply. This keeps the combination from rolling away with no brakes. It is a key safety device tested during the pre-trip inspection.

Question 13Combination vehicle inspection and coupling/uncoupling

You are coupling to a trailer and the fifth wheel jaws will not close around the kingpin. Which cause is most likely?

  1. The air lines are connected
  2. The trailer brakes are set
  3. The kingpin is not centered in the fifth wheel throat or the jaws are open and not reset Correct answer.
  4. The trailer is too high and the kingpin passes over the fifth wheel

Explanation

If the jaws will not close, the kingpin is usually not centered in the throat, or the jaws were left open and need to be reset. Backing in slightly off-center or with the jaws in the wrong position prevents proper capture. Recheck alignment and jaw position before trying again.

Question 14Combination vehicle inspection and coupling/uncoupling

What is the correct order for the final steps of coupling a tractor to a trailer?

  1. Secure release latch, connect air lines, pull test, raise landing gear
  2. Pull test, raise landing gear, secure release latch, connect air lines Correct answer.
  3. Connect air lines, raise landing gear, pull test, secure latch
  4. Pull test, connect air lines, secure release latch, raise landing gear

Explanation

After the jaws close, secure the release latch, perform the pull test, then raise the landing gear to travel position. The air lines are connected before the pull test so the trailer brakes can be set. The sequence ensures the coupling is verified before the trailer is left unsupported.

Question 15Combination vehicle inspection and coupling/uncoupling

During uncoupling, after you have lowered the landing gear and released the fifth wheel jaws, what should you do next?

  1. Disconnect the air lines before pulling out
  2. Pull the tractor forward slowly until it clears the trailer Correct answer.
  3. Release the trailer brakes and drive away
  4. Lower the landing gear further to lift the trailer

Explanation

Once the jaws are released and the landing gear supports the trailer, pull the tractor forward slowly until it is clear of the trailer. Pulling out gently avoids damaging the kingpin or landing gear. Air lines and the electrical cord are disconnected before pulling out, and the trailer brakes remain set.

Question 16Combination vehicle inspection and coupling/uncoupling

Why must the trailer air supply line be disconnected before the tractor is pulled away during uncoupling?

  1. To release the trailer spring brakes
  2. To allow the trailer lights to stay on
  3. To prevent the lines from being torn or damaged as the tractor separates Correct answer.
  4. To reset the fifth wheel jaws

Explanation

If the air lines remain connected when the tractor pulls away, they will stretch and tear, damaging the couplers and lines. Disconnecting them first protects the equipment. The electrical cord should also be disconnected before separation.

Question 17Combination vehicle inspection and coupling/uncoupling

When checking the coupling during the pre-trip inspection, you look under the trailer and see a gap between the trailer apron and the fifth wheel. What does this suggest?

  1. The landing gear is raised correctly
  2. The kingpin is too long for the fifth wheel
  3. The coupling is secure because the jaws are closed
  4. The trailer may not be fully seated on the fifth wheel Correct answer.

Explanation

A visible gap between the trailer apron and the fifth wheel plate suggests the trailer is not fully seated, which can mean the kingpin is not properly captured or the height is wrong. The trailer should rest firmly on the fifth wheel. A gap warrants rechecking the coupling before driving.

Question 18Combination vehicle inspection and coupling/uncoupling

Which component helps prevent the fifth wheel jaws from opening through unintended movement of the release handle?

  1. The landing gear
  2. The kingpin and the fifth wheel mounting
  3. The safety latch on the release handle Correct answer.
  4. The trailer air supply line

Explanation

The safety latch on the release handle prevents the handle from moving and the jaws from opening unintentionally. It is a critical safety device checked during coupling, but it is not an independent connection that retains the trailer after structural jaw failure.

Question 19Combination vehicle inspection and coupling/uncoupling

What should you check about the trailer landing gear during the walk-around inspection?

  1. That the gear is lowered to the ground
  2. That the gear is lubricated with air tool oil
  3. That the crank is fully raised and the gear is secure in the travel position Correct answer.
  4. That the crank is removed and stored in the cab

Explanation

During the walk-around, the landing gear should be fully raised and secured in the travel position so it does not drag or strike the road. A crank left down or gear extended is a hazard. The gear is lowered only when the trailer is parked or being uncoupled.

Question 20Combination vehicle inspection and coupling/uncoupling

You are inspecting a combination vehicle and notice the trailer's electrical cord is pinched between the tractor and trailer. What is the correct action?

  1. Disconnect the cord and drive without trailer lights
  2. Ignore it because the cord is flexible
  3. Cut the cord and splice it later
  4. Reroute the cord so it is not pinched or chafed before driving Correct answer.

Explanation

A pinched or chafed electrical cord can short out and cause trailer lights to fail, which is a safety hazard. The cord should be rerouted so it hangs free and is supported, not crushed between the units. Driving without trailer lights is unsafe and illegal.

Question 21Combination vehicle inspection and coupling/uncoupling

During the pre-trip inspection, how do you test that the trailer brakes hold when the trailer air supply is released?

  1. With the trailer brakes set, try to pull forward gently and confirm the trailer does not move Correct answer.
  2. Disconnect the electrical cord and watch the lights
  3. Release the tractor parking brake and roll backward
  4. Start the engine and listen for the compressor to cycle

Explanation

With the trailer brakes applied, a gentle pull forward should not move the trailer, confirming the brakes hold. This is the practical test of the trailer emergency and service brakes. Listening to the compressor or rolling backward does not verify brake holding.

Question 22Combination vehicle inspection and coupling/uncoupling

What is the correct position of the tractor's fifth wheel height relative to the trailer when preparing to couple?

  1. The fifth wheel should be at a height that lets the trailer apron clear it as the tractor backs under Correct answer.
  2. The fifth wheel should be raised as high as possible
  3. The fifth wheel height does not matter
  4. The fifth wheel should be lowered below the trailer frame

Explanation

The fifth wheel must be positioned so the trailer apron clears it as the tractor backs under, allowing the kingpin to enter the throat and the jaws to close. If the fifth wheel is too high, it strikes the trailer; too low, and the trailer may not seat. Height adjustment is part of proper coupling preparation.

Question 23Combination vehicle inspection and coupling/uncoupling

After coupling and completing the pull test, you raise the landing gear. Why must the crank be secured in the travel position?

  1. To keep the air lines connected
  2. To keep the gear from dragging or striking the road while driving Correct answer.
  3. To hold the fifth wheel jaws closed
  4. To keep the trailer brakes applied

Explanation

The landing gear must be fully raised and the crank secured so the gear does not drag or strike the road, which could damage it or cause loss of control. A crank left down can swing out and hit objects. Securing it is part of the final coupling steps.

Question 24Combination vehicle inspection and coupling/uncoupling

You are coupling in the dark and cannot clearly see the fifth wheel jaws. What is the safest approach?

  1. Use a light to visually confirm the jaws are closed around the kingpin and the latch is engaged Correct answer.
  2. Skip the visual check and rely on the pull test alone
  3. Have someone stand behind the trailer and signal when to stop
  4. Assume the jaws closed because you heard a click

Explanation

Visual confirmation with a light is required to ensure the jaws are closed around the kingpin and the release handle and latch are secure. A click alone does not guarantee proper engagement. The pull test supplements, but does not replace, the visual check.

Question 25Combination vehicle inspection and coupling/uncoupling

Which of these is a required check of the trailer suspension during the combination vehicle walk-around?

  1. That the tires are inflated to the maximum sidewall pressure
  2. That the springs, hangers, and U-bolts are intact and not cracked or missing Correct answer.
  3. That the trailer is loaded to capacity
  4. That the mud flaps are removed

Explanation

The walk-around includes checking that leaf springs, hangers, shackles, and U-bolts are intact, with no cracks, missing parts, or shifted components. A broken suspension part can cause loss of control. Load weight and tire pressure settings are separate considerations, and mud flaps must be present, not removed.

Question 26Combination vehicle inspection and coupling/uncoupling

Before backing under a trailer to couple, what should you check about the trailer's height relative to the fifth wheel?

  1. The trailer apron should be slightly higher than the fifth wheel so the plate slides under it Correct answer.
  2. The trailer should be raised so the kingpin clears the fifth wheel plate entirely
  3. The trailer height does not matter as long as the kingpin is greased
  4. The trailer apron should be slightly lower than the fifth wheel so the plate lifts it

Explanation

The trailer must sit slightly high so the fifth wheel plate passes under the apron and the kingpin enters the jaws rather than striking the plate. If the trailer is too low, the tractor will push the trailer backward instead of coupling.

Question 27Combination vehicle inspection and coupling/uncoupling

When you perform the pull test after coupling, what are you actually confirming?

  1. That the fifth wheel jaws have locked around the kingpin Correct answer.
  2. That the electrical cord has enough slack
  3. That the landing gear has been fully raised
  4. That the trailer brakes release smoothly when air is supplied

Explanation

The pull test uses gentle forward tugging against the locked trailer brakes to prove the kingpin is captured by the jaws. If the jaws are not locked, the trailer will not move with the tractor or the coupling will separate.

Question 28Combination vehicle inspection and coupling/uncoupling

What is the purpose of the air line color coding on a combination vehicle?

  1. To indicate the line that must be disconnected first
  2. To show which line carries the higher pressure
  3. To mark which line is the older of the two
  4. To identify the service and emergency (supply) lines so they are not cross-connected Correct answer.

Explanation

The service line is typically blue and the emergency/supply line is red, which helps you connect each line to its matching gladhand. Cross-connecting them prevents proper brake operation and can leave the trailer without emergency braking.

Question 29Combination vehicle inspection and coupling/uncoupling

During the walk-around inspection, how should the trailer's gladhands be positioned when they are not connected?

  1. Seated on dummy couplers to keep out dirt and moisture Correct answer.
  2. Hanging free so they can drain
  3. Resting on the tractor frame
  4. Taped together to prevent movement

Explanation

Unused gladhands should be stored on the dummy couplers, which seal the openings and keep dirt and water out of the air system. Contamination in the lines can cause brake valves to stick or leak.

Question 30Combination vehicle inspection and coupling/uncoupling

Which of these is part of the tractor-side coupling inspection before you back under a trailer?

  1. Checking that the fifth wheel jaws are open and the plate is greased Correct answer.
  2. Checking the trailer's tire tread depth
  3. Checking the trailer's brake adjustment
  4. Checking that the trailer lights are operating

Explanation

Before coupling, the fifth wheel jaws must be open and ready to receive the kingpin, and the plate should be lubricated so the trailer pivots properly. Trailer lights, brakes, and tires are checked after coupling as part of the combination inspection.

Question 31Combination vehicle inspection and coupling/uncoupling

When you release the trailer air supply (red knob) during the coupling sequence, what should happen if the trailer is properly connected?

  1. The trailer spring brakes should set and hold the trailer Correct answer.
  2. The landing gear should retract automatically
  3. The tractor should shut off
  4. The trailer brakes should release and the trailer should roll

Explanation

Pulling the red knob cuts air to the trailer emergency line, which causes the trailer spring brakes to apply. This is the check that confirms the emergency line is connected and the trailer brakes will hold if the lines separate.

Question 32Combination vehicle inspection and coupling/uncoupling

Why should you chock the trailer wheels before uncoupling?

  1. To keep the landing gear from sinking into soft ground
  2. To keep the trailer from rolling when the tractor is pulled away Correct answer.
  3. To make the fifth wheel jaws release more easily
  4. To hold the air lines in place

Explanation

Once the tractor is removed, nothing else holds the trailer in place, so chocks prevent it from rolling on any slope. A trailer that rolls can cause serious injury or damage.

Question 33Combination vehicle inspection and coupling/uncoupling

What does the trailer hand valve (trolley valve) do on a combination vehicle?

  1. It dumps air from the tractor tanks
  2. It applies the trailer service brakes only Correct answer.
  3. It releases the trailer spring brakes
  4. It sets the tractor parking brakes

Explanation

The hand valve applies only the trailer service brakes, which is useful for testing the trailer brake connection. It is not a parking brake and does not release spring brakes.

Question 34Combination vehicle inspection and coupling/uncoupling

You are coupling and notice the trailer kingpin is worn with visible flat spots. What is the correct action?

  1. Couple anyway and note it for the next driver
  2. Report the defect and do not couple to the trailer Correct answer.
  3. Grease the kingpin heavily and couple
  4. Tap the kingpin with a hammer to reshape it

Explanation

A worn or damaged kingpin may not be securely held by the fifth wheel jaws, creating a risk of separation. The defect must be reported and the trailer taken out of service until repaired.

Question 35Combination vehicle inspection and coupling/uncoupling

After backing under the trailer and hearing the fifth wheel lock, what should you do before raising the landing gear?

  1. Pull forward slowly to check the connection, then set the parking brake Correct answer.
  2. Connect the air lines, then do the pull test
  3. Release the trailer air supply knob and check the brakes
  4. Connect the electrical cord and test the lights

Explanation

The pull test comes right after coupling and before raising the landing gear, so the trailer stays supported if the connection fails. Only after the tug confirms the lock should you proceed to connect lines and raise the gear.

Question 36Combination vehicle inspection and coupling/uncoupling

While inspecting the coupling, you notice the fifth wheel release handle is pulled out and the safety latch is not engaged. What does this indicate?

  1. The jaws may not be locked and the coupling is unsafe Correct answer.
  2. The jaws are locked and the handle is in the normal travel position
  3. The air lines are cross-connected
  4. The trailer brakes are still applied

Explanation

A release handle that is out indicates the locking mechanism may not be fully engaged, and the safety latch should always be in place to prevent accidental release. The vehicle should not be moved until the coupling is corrected.

Question 37Combination vehicle inspection and coupling/uncoupling

What is the correct procedure for disconnecting the air lines and electrical cord during uncoupling?

  1. Disconnect the electrical cord first, then the air lines
  2. Leave the lines connected until the tractor is pulled away
  3. Disconnect all lines at the same time
  4. Disconnect the air lines first, then the electrical cord Correct answer.

Explanation

The air lines should be disconnected and stored on the dummy couplers before the electrical cord, so the trailer brakes remain set while you work. Pulling the tractor away with lines attached will damage them.

Question 38Combination vehicle inspection and coupling/uncoupling

You are inspecting a combination vehicle and find the trailer's spring brake chambers have a broken clamp band. What should you do?

  1. Tie the chamber with wire and continue
  2. Reduce the trailer load and continue
  3. Report the defect and place the trailer out of service Correct answer.
  4. Continue the trip but avoid hard braking

Explanation

A broken clamp band on a spring brake chamber means the spring is not safely contained and the brake may fail. This is an out-of-service defect that must be repaired before the vehicle is used.

Question 39Combination vehicle inspection and coupling/uncoupling

During the walk-around, you find the trailer's landing gear crank handle is missing. What is the correct response?

  1. Raise the gear by hand and continue
  2. Leave the gear down and drive slowly
  3. Note the defect and have the gear repaired before operating Correct answer.
  4. Use a pipe wrench to raise the gear and continue

Explanation

Without the crank, the landing gear cannot be raised or lowered safely, and driving with the gear down damages the equipment. The defect should be repaired before the vehicle is operated.

Question 40Combination vehicle inspection and coupling/uncoupling

What does the tractor protection valve do when the trailer is uncoupled and the air lines are disconnected?

  1. It closes the fifth wheel jaws
  2. It automatically applies the trailer parking brakes
  3. It keeps the tractor air system from losing all its air through the open gladhands Correct answer.
  4. It shuts off the electrical system

Explanation

The tractor protection valve closes off the tractor air supply when the trailer lines are disconnected or pressure drops, preserving enough air for the tractor brakes. Without it, the tractor would lose air rapidly through the open couplers.

Question 41Combination vehicle inspection and coupling/uncoupling

You are coupling at night and the trailer's reflective tape is damaged and the lights are dim. What should you do?

  1. Continue only on roads with street lighting
  2. Use the tractor's headlights to illuminate the trailer
  3. Couple and drive with the hazard flashers on
  4. Repair or replace the tape and lights before operating Correct answer.

Explanation

Damaged reflective tape and dim lights reduce the trailer's visibility to other drivers, which is a safety defect. The lights and tape must be repaired before the vehicle is placed in service.

Question 42Combination vehicle inspection and coupling/uncoupling

When inspecting the coupling, how do you verify that the trailer's emergency (supply) line is connected to the correct gladhand?

  1. Check that both lines are connected to the same coupler
  2. Check that neither line is connected until after the pull test
  3. Check that the blue line is connected to the emergency gladhand
  4. Check that the red line is connected to the emergency gladhand on the trailer Correct answer.

Explanation

The emergency/supply line is red and must connect to the emergency gladhand so that supply air charges the trailer system. The blue service line connects to the service gladhand. Correct color matching prevents cross-connection.

Question 43Combination vehicle inspection and coupling/uncoupling

During the pre-trip inspection, how do you check the trailer's spring brakes for proper application?

  1. Push in the red knob and listen for air escaping
  2. Pull out the red knob and try to move the tractor against the trailer Correct answer.
  3. Release the tractor parking brake and roll forward
  4. Press the foot brake and watch the trailer wheels

Explanation

Pulling the red trailer air supply knob should set the trailer spring brakes, and attempting to move the tractor confirms they hold. This verifies the emergency line is connected and the brakes function.

Question 44Combination vehicle inspection and coupling/uncoupling

What is the correct order of steps when uncoupling a tractor from a trailer?

  1. Lower landing gear, chock wheels, release fifth wheel jaws, disconnect lines, pull away Correct answer.
  2. Chock wheels, disconnect lines, release jaws, lower landing gear, pull away
  3. Disconnect lines, release jaws, chock wheels, lower landing gear, pull away
  4. Release jaws, lower landing gear, chock wheels, disconnect lines, pull away

Explanation

The trailer must be supported before the tractor is removed, so the landing gear goes down and the wheels are chocked first. Then the jaws are released, the lines are disconnected, and the tractor is pulled away.

Question 45Combination vehicle inspection and coupling/uncoupling

You are inspecting the trailer suspension and notice a cracked leaf spring. What is the correct action?

  1. Reduce the load and continue
  2. Tie the spring with chain and continue
  3. Report the defect and do not operate the vehicle Correct answer.
  4. Continue if the crack is small

Explanation

A cracked leaf spring can fail completely and cause loss of control or axle misalignment. It is an out-of-service defect that must be repaired before the vehicle is operated.

Question 46Combination vehicle inspection and coupling/uncoupling

When checking the fifth wheel during the walk-around, what should you look for on the mounting bolts?

  1. That they are painted to match the frame
  2. That they are tight and free of rust or cracks Correct answer.
  3. That they are removed for inspection
  4. That they are loose enough to allow movement

Explanation

The fifth wheel mounting bolts must be tight with no rust, cracks, or missing fasteners, because a loose fifth wheel can shift or separate from the frame. Loose or damaged mounting hardware is a serious safety defect.

Question 47Combination vehicle inspection and coupling/uncoupling

You are coupling and the trailer's kingpin is too high for the fifth wheel jaws to engage. What is the most likely cause?

  1. The fifth wheel jaws are worn
  2. The trailer is set too high relative to the fifth wheel Correct answer.
  3. The landing gear is fully raised
  4. The air lines are cross-connected

Explanation

If the trailer sits too high, the kingpin passes above the jaws and the fifth wheel plate cannot capture it. Lowering the trailer so the apron sits slightly above the plate allows the kingpin to enter the jaws.

Question 48Combination vehicle inspection and coupling/uncoupling

During a pre-trip inspection, the trailer's spring brakes release when the red knob is pushed in, but the trailer rolls when the hand valve is applied. What does this suggest?

  1. The electrical cord is disconnected
  2. The trailer spring brakes are working correctly
  3. The tractor protection valve is stuck open
  4. The emergency line is connected but the service line is not delivering air Correct answer.

Explanation

The hand valve applies the trailer service brakes through the blue service line, so a trailer that rolls when the valve is applied suggests the service line is not delivering air. The spring brakes releasing confirms the emergency line is functioning.

Question 49Combination vehicle inspection and coupling/uncoupling

After a pull test confirms the coupling, you connect the air lines and hear a continuous leak at the gladhand. What should you do?

  1. Disconnect the service line and continue
  2. Stop and repair or reseat the connection before operating Correct answer.
  3. Continue and monitor the leak
  4. Increase engine RPM to maintain pressure

Explanation

A continuous leak at the gladhand can drain the air system and reduce braking ability, so the connection must be corrected before operating. Reseating the coupler or replacing a damaged seal resolves the problem.

Question 50Combination vehicle inspection and coupling/uncoupling

You are inspecting a combination vehicle and find the trailer's ABS lamp stays on after the ignition is cycled. What does this indicate?

  1. The electrical cord is disconnected
  2. The ABS system has a fault and should be checked before operating Correct answer.
  3. The trailer is not coupled properly
  4. The trailer brakes are fully applied

Explanation

An ABS lamp that remains on after the self-test indicates a fault in the trailer's antilock brake system, which should be diagnosed before operating. ABS faults can affect braking performance during hard stops.