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Maryland CDL Combination study materials
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Maryland CDL Combination practice questions

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Question 1Combination vehicle inspection and coupling/uncoupling

Before backing a tractor under a trailer to couple, how should the trailer apron height compare with the fifth wheel plate?

  1. The trailer apron should be slightly higher than the fifth wheel so the plate rides under the trailer
  2. The trailer apron height does not matter as long as the trailer brakes are set
  3. The trailer apron should be exactly level with the top of the fifth wheel
  4. The trailer apron should be low enough that the tractor raises the trailer slightly as the fifth wheel slides underneath Correct answer.

Explanation

Set the trailer low enough for the tractor to lift it slightly as the fifth wheel slides under the trailer apron. The fifth wheel must capture the projecting kingpin, not ride over it. A trailer that is too high may not couple correctly; one that is too low can be struck and damaged by the tractor.

Question 2Combination vehicle inspection and coupling/uncoupling

After the fifth wheel jaws close on the kingpin, what is the correct next step before you release the trailer brakes?

  1. Connect the electrical cord first
  2. Do the tug test by pulling gently against the locked trailer brakes Correct answer.
  3. Lower the landing gear fully to the ground
  4. Pull the tractor forward slowly to test the latch

Explanation

The tug test confirms the jaws have locked on the kingpin: with the trailer brakes set, you pull gently against them and feel the tractor resist. Only after the coupling is verified should you connect lines and raise the landing gear.

Question 3Combination vehicle inspection and coupling/uncoupling

Which item is part of the pre-trip inspection specific to a combination vehicle rather than a single-unit truck?

  1. The fifth wheel and its mounting bolts Correct answer.
  2. The steering wheel free play
  3. The passenger seat belts
  4. The windshield wiper blades

Explanation

Combination vehicles add coupling hardware that single units lack: the fifth wheel, its mounting bolts, the kingpin, the locking jaws, and the air and electrical connections between units. Wiper blades, steering free play, and seat belts are checked on any vehicle.

Question 4Combination vehicle inspection and coupling/uncoupling

When uncoupling a tractor-trailer, in what order should you release the coupling?

  1. Disconnect the lines, release the fifth wheel jaws, then lower the landing gear
  2. Release the fifth wheel jaws, then lower the landing gear, then disconnect the lines
  3. Lower the landing gear, disconnect the air and electrical lines, then release the fifth wheel jaws Correct answer.
  4. Set the trailer brakes, release the fifth wheel jaws, then disconnect the lines

Explanation

The trailer must be supported on its landing gear before the tractor is released, and the air lines must be disconnected before the tractor pulls away so they are not torn. The fifth wheel is released last, just before pulling the tractor clear.

Question 5Combination vehicle inspection and coupling/uncoupling

When should you set the trailer parking brakes during the coupling procedure?

  1. After the landing gear is raised
  2. Before backing the tractor under the trailer Correct answer.
  3. Only after the air lines are connected
  4. After the tractor is fully backed under and locked

Explanation

Setting the trailer brakes before backing keeps the trailer from rolling when the tractor contacts it. The brakes also make the tug test possible, since the tractor pulls against them to confirm the jaws are locked.

Question 6Combination vehicle inspection and coupling/uncoupling

What does the air line color coding indicate on a tractor-trailer combination?

  1. Both lines are interchangeable and color is cosmetic
  2. Blue is service air and red is emergency air
  3. Red is emergency (supply) air and blue is service air Correct answer.
  4. Green is service air and black is emergency air

Explanation

The red line is the emergency or supply line that charges the trailer system, and the blue line is the service line that carries application pressure. Correct color matching prevents cross-connection and brake failure.

Question 7Combination vehicle inspection and coupling/uncoupling

Why must the landing gear be raised completely after coupling?

  1. To prevent it from striking the ground or railroad crossings while moving Correct answer.
  2. To allow the fifth wheel to rotate freely
  3. To reduce wind resistance at highway speed
  4. To keep the trailer level while parked

Explanation

Landing gear left down can catch on pavement, railroad crossings, or dock edges and cause serious damage or a crash. Once the tractor supports the trailer, the gear must be fully retracted and the crank handle secured.

Question 8Combination vehicle inspection and coupling/uncoupling

During a pre-trip inspection of the coupling, which condition of the fifth wheel mounting requires the vehicle to be placed out of service?

  1. A missing or loose mounting bolt Correct answer.
  2. Light surface rust on the plate
  3. Grease on the top of the plate
  4. Minor paint wear around the jaws

Explanation

The fifth wheel carries the trailer load through its mounting bolts, so a missing or loose bolt compromises the connection and must be corrected before operation. Surface rust, grease, and paint wear are normal and not defects.

Question 9Combination vehicle inspection and coupling/uncoupling

You back under a trailer, hear the jaws close, and the tug test holds. What additional visual check confirms a proper coupling?

  1. The landing gear is still touching the ground
  2. The trailer apron rests above the plate with a gap visible
  3. The air lines are crossed
  4. The fifth wheel plate is flush under the trailer with the jaws closed around the kingpin Correct answer.

Explanation

Looking under the trailer, the fifth wheel should be flat against the trailer apron with no gap, and the locking jaws should be visibly closed around the kingpin. A gap or open jaws means the coupling is incomplete even if the tug test felt solid.

Question 10Combination vehicle inspection and coupling/uncoupling

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

  1. To hold the air lines in place during travel
  2. To secure the landing gear crank
  3. To keep the locking jaws from opening accidentally Correct answer.
  4. To lock the trailer brakes when parked

Explanation

The safety latch is a secondary device that prevents the locking jaws from releasing the kingpin in service. If it is missing or broken, the fifth wheel may open unexpectedly and separate the trailer.

Question 11Combination vehicle inspection and coupling/uncoupling

A driver connects the air lines but the trailer brakes will not release and the low air warning sounds. What is the most likely cause?

  1. The fifth wheel is not greased
  2. The landing gear is still down
  3. The trailer is overloaded
  4. The service line is connected to the emergency gladhand Correct answer.

Explanation

Cross-connecting the service and emergency lines prevents the trailer system from charging properly, so the spring brakes stay applied. Correct color matching (red emergency, blue service) is the fix.

Question 12Combination vehicle inspection and coupling/uncoupling

When performing the tug test, what should you do with the trailer brakes?

  1. Leave them in whatever position they were in
  2. Pump them repeatedly during the pull
  3. Set them so the trailer resists the tractor Correct answer.
  4. Release them so the trailer can roll

Explanation

The trailer brakes must be set so the trailer cannot roll while you pull gently forward. The tractor should feel resistance and stop; if the tractor moves freely, the coupling is not secure.

Question 13Combination vehicle inspection and coupling/uncoupling

What is the correct procedure for checking that the trailer spring brakes apply when the air supply is lost?

  1. Disconnect the electrical cord and watch the lights
  2. Shut off the engine and listen for leaks only
  3. Step on the service brake and hold it
  4. Pull the tractor protection valve to the emergency position and watch for the trailer brakes to set Correct answer.

Explanation

Pulling the tractor protection valve to emergency simulates a loss of air supply, and the trailer spring brakes should apply automatically. This confirms the emergency braking function works before you drive.

Question 14Combination vehicle inspection and coupling/uncoupling

How much gap should exist between the tractor frame and the trailer apron after a proper coupling?

  1. A gap of one foot indicates a good seal
  2. There should be no gap; the plate should be tight against the apron Correct answer.
  3. Gap size is irrelevant to coupling quality
  4. A gap of several inches is normal

Explanation

No gap should be visible between the fifth wheel plate and the trailer apron; a gap means the trailer is not seated on the plate and the coupling is unsafe. This is one of the key visual checks after backing under.

Question 15Combination vehicle inspection and coupling/uncoupling

When should the electrical cord be connected during coupling?

  1. Before backing under the trailer
  2. After the trailer is parked for the night
  3. After the coupling is verified and before the landing gear is raised Correct answer.
  4. Only after the tractor is moving

Explanation

The electrical cord is connected after the mechanical coupling is confirmed, along with the air lines, so the trailer lights and ABS work before you move. Connecting it before backing risks damage during the coupling maneuver.

Question 16Combination vehicle inspection and coupling/uncoupling

Which condition of the kingpin requires the trailer to be taken out of service?

  1. Normal surface discoloration
  2. A cracked or worn kingpin Correct answer.
  3. A light coating of grease
  4. Paint wear on the kingpin head

Explanation

A cracked or excessively worn kingpin can fail under load and allow the trailer to separate from the tractor. Grease, paint wear, and discoloration are normal and not grounds for removal from service.

Question 17Combination vehicle inspection and coupling/uncoupling

During uncoupling, why should you pull the tractor forward slightly after releasing the fifth wheel jaws?

  1. To charge the air system
  2. To test the trailer brakes
  3. To let the trailer settle onto the landing gear and clear the tractor frame Correct answer.
  4. To align the kingpin for the next coupling

Explanation

Pulling forward slowly after releasing the jaws lets the trailer settle onto its landing gear and moves the tractor clear of the kingpin. Pulling away abruptly can damage the trailer or the tractor frame.

Question 18Combination vehicle inspection and coupling/uncoupling

What should you check about the landing gear before coupling to a parked trailer?

  1. That it is fully raised
  2. That the crank handle is removed
  3. That it is greased and free of rust
  4. That it is firmly on the ground and the trailer is stable Correct answer.

Explanation

Before backing under, the landing gear must be down and firmly supporting the trailer so it does not shift or drop during coupling. A trailer resting on unstable or partially raised gear is a hazard.

Question 19Combination vehicle inspection and coupling/uncoupling

A driver hears the fifth wheel jaws close but the safety latch will not engage. What is the correct action?

  1. Tie the latch with wire and proceed
  2. Do not move the vehicle until the latch is repaired or engaged Correct answer.
  3. Drive slowly and check it at the next stop
  4. Ignore it because the jaws are already closed

Explanation

The safety latch is the secondary lock that keeps the jaws from opening; if it will not engage, the coupling is not secure and the vehicle must not be moved. The defect must be corrected before operation.

Question 20Combination vehicle inspection and coupling/uncoupling

When backing under a trailer at night, what is the best way to confirm alignment with the kingpin?

  1. Back quickly to reduce exposure time
  2. Use a guide or get out and check alignment before backing Correct answer.
  3. Rely on the mirrors alone
  4. Sound the horn continuously

Explanation

At night, poor visibility makes it hard to judge alignment, so using a guide or stopping to check before backing reduces the risk of missing the kingpin. Backing blind or fast increases the chance of damage or injury.

Question 21Combination vehicle inspection and coupling/uncoupling

What is the consequence of coupling to a trailer whose kingpin is too high relative to the fifth wheel?

  1. The air lines will not connect
  2. The trailer brakes will not release
  3. The fifth wheel may pass under the trailer without latching, and the tractor can strike the trailer Correct answer.
  4. The landing gear will not retract

Explanation

If the trailer sits too high, the fifth wheel can slide beneath the trailer without the jaws engaging the kingpin, and the tractor may strike the trailer nose. The trailer must be lowered so the plate rides up and the jaws close.

Question 22Combination vehicle inspection and coupling/uncoupling

After coupling and connecting the lines, you release the tractor parking brake but the combination will not roll. Which combination of causes is most consistent with this symptom?

  1. The landing gear crank is missing
  2. Trailer spring brakes still applied because the emergency line is not charged Correct answer.
  3. The electrical cord is connected
  4. The fifth wheel is over-greased

Explanation

If the emergency line is not properly connected or charged, the trailer spring brakes remain applied and hold the combination. Checking line connections and air pressure is the correct diagnostic step.

Question 23Combination vehicle inspection and coupling/uncoupling

During a pre-trip inspection, you find the fifth wheel plate is not sitting flat on the tractor frame and shows a gap at the mounting. What does this indicate?

  1. That the plate needs more grease
  2. Normal flex in the mounting
  3. That the trailer is overloaded
  4. A loose or improper mounting that must be corrected before operation Correct answer.

Explanation

A gap or uneven seating at the fifth wheel mounting indicates loose or improper mounting, which can allow the fifth wheel to shift or fail under load. The vehicle must not be operated until the mounting is corrected.

Question 24Combination vehicle inspection and coupling/uncoupling

A driver uncouples on a slope and the trailer rolls slightly after the jaws release. What step was most likely missed?

  1. The trailer parking brakes were not set before releasing the jaws Correct answer.
  2. The electrical cord was connected
  3. The fifth wheel was greased
  4. The landing gear was raised too far

Explanation

Setting the trailer parking brakes before releasing the fifth wheel jaws prevents the trailer from rolling on a slope. If the brakes were not set, the trailer can move as soon as the tractor releases it.

Question 25Combination vehicle inspection and coupling/uncoupling

Which set of checks best confirms a complete and safe coupling before departure?

  1. Tug test only
  2. Air line connection only
  3. Visual check only
  4. Tug test, visual check of jaws and gap, air line connection, and electrical connection Correct answer.

Explanation

A complete coupling check combines the tug test, a visual confirmation that the jaws are closed with no gap, and proper connection of both air lines and the electrical cord. Any one check alone can miss a defect.

Question 26Combination vehicle inspection and coupling/uncoupling

On a combination vehicle, what is the primary purpose of the trailer supply (emergency) line?

  1. It supplies air only to the trailer service brakes when the foot valve is pressed
  2. It charges the trailer's spring brake reservoirs and signals a loss of air so the trailer brakes apply Correct answer.
  3. It carries the electrical signal that operates the trailer stop lamps
  4. It vents air from the trailer tires to regulate tire pressure

Explanation

The supply line is the emergency line: it charges the trailer air tanks and, when pressure drops or the line separates, causes the trailer spring brakes to set. The service line is the separate line that delivers air to apply the trailer brakes during normal braking.

Question 27Combination vehicle inspection and coupling/uncoupling

Which coupling component transfers the trailer's weight to the tractor frame while allowing the combination to pivot?

  1. The fifth wheel Correct answer.
  2. The glad hands
  3. The electrical cord
  4. The trailer spring brakes

Explanation

The fifth wheel is the horseshoe-shaped plate mounted on the tractor frame that supports the trailer's weight through the kingpin and lets the combination pivot in turns. Glad hands join air lines and do not carry weight.

Question 28Combination vehicle inspection and coupling/uncoupling

How should the trailer supply line and service line be routed after coupling?

  1. Supported so they cannot drag, kink, or rub against the tractor frame or trailer Correct answer.
  2. Left hanging free so they can swing clear during turns
  3. Looped tightly around the trailer apron to keep them short
  4. Crossed so each line reaches the opposite side of the trailer

Explanation

Air lines must be supported and routed so they do not drag on the ground, kink, or chafe against sharp edges, which can cause a leak or a breakaway. A tight loop or a free swing invites wear and separation.

Question 29Combination vehicle inspection and coupling/uncoupling

Before backing under a parked trailer, what should you do with the trailer's spring brakes?

  1. Apply them only after the kingpin is engaged
  2. Leave them applied so the trailer stays put during coupling Correct answer.
  3. Release them so the trailer can roll into alignment
  4. Chock the wheels instead and leave the brakes released

Explanation

The trailer spring brakes should be set (applied) so the trailer cannot roll while you back under it. The brakes are released only after the kingpin is locked and the air lines are connected.

Question 30Combination vehicle inspection and coupling/uncoupling

During uncoupling, what should you do with the trailer spring brakes before pulling the tractor out from under the trailer?

  1. Release them so the trailer can settle onto the landing gear
  2. Set them so the trailer cannot roll once the tractor is removed Correct answer.
  3. Disconnect the supply line first to apply them automatically
  4. Pump them several times to bleed residual air

Explanation

The trailer spring brakes must be set before the tractor is pulled out, so the trailer stays parked on its landing gear. Disconnecting the supply line will eventually set them, but the driver should deliberately set them as part of the uncoupling sequence.

Question 31Combination vehicle inspection and coupling/uncoupling

What is the purpose of the trailer hand valve (trolley valve) on a combination vehicle?

  1. To release the trailer spring brakes during coupling
  2. To set the tractor parking brake automatically
  3. To apply only the tractor brakes for a parking check
  4. To test the trailer brakes independently of the tractor brakes Correct answer.

Explanation

The hand valve lets the driver apply the trailer service brakes alone, which is useful for checking that trailer brakes work. It does not park the vehicle and does not release spring brakes.

Question 32Combination vehicle inspection and coupling/uncoupling

When you connect the electrical cord to the trailer, what should you check about the plug?

  1. That the pins are coated with grease before insertion
  2. That the cord is wrapped around the air lines for support
  3. That the receptacle cap is left open to drain moisture
  4. That the plug is fully seated and the cord has enough slack for turns Correct answer.

Explanation

The plug must seat fully in the receptacle so the trailer lights work reliably, and the cord needs enough slack to avoid pulling apart in turns. The cap should be closed to keep out water and dirt.

Question 33Combination vehicle inspection and coupling/uncoupling

What does the red trailer ABS warning lamp on the trailer tell you?

  1. That the trailer spring brakes are applied
  2. That a trailer ABS fault has been detected and should be checked Correct answer.
  3. That the trailer air tanks are fully charged
  4. That the trailer ABS is functioning normally and the lamp will stay lit

Explanation

A trailer ABS lamp that stays on indicates an ABS fault in the trailer system, which should be diagnosed before the vehicle is operated. A brief lamp check at start-up is normal; a continuous light is not.

Question 34Combination vehicle inspection and coupling/uncoupling

After coupling and connecting the lines, how do you confirm the trailer service brakes respond to the foot valve?

  1. Release the tractor parking brake and listen for air escaping
  2. Open a glad hand and check for a rush of air
  3. Press the foot brake and have someone watch the trailer brakes apply, or feel the combination resist rolling Correct answer.
  4. Set the trailer spring brakes and pull against them in low gear

Explanation

Applying the foot valve should apply the trailer service brakes, which can be confirmed by an observer or by the combination resisting movement. This verifies the service line is connected and the brakes work.

Question 35Combination vehicle inspection and coupling/uncoupling

You are coupling on a slight grade. What is the safest way to keep the trailer from rolling while you back under it?

  1. Rely on the trailer spring brakes and chock the trailer wheels Correct answer.
  2. Leave the trailer brakes released and use the tractor's brakes only
  3. Place the transmission in neutral and let the trailer settle
  4. Set the tractor parking brake and leave the trailer free

Explanation

On a grade, the trailer spring brakes should be set and the wheels chocked as a backup so the trailer cannot roll during coupling. The tractor's brakes alone do not secure the trailer.

Question 36Combination vehicle inspection and coupling/uncoupling

During a pre-trip inspection, you notice the trailer air lines are routed so they cross each other between the tractor and trailer. What is the concern?

  1. Crossed lines improve air flow and are preferred
  2. Crossed lines have no effect on the air system
  3. The lines will chafe and may leak or separate, so they should be rerouted Correct answer.
  4. Crossed lines are required to keep the glad hands sealed

Explanation

Crossed or improperly routed lines rub against each other and nearby surfaces, which can wear through the hose and cause a leak or breakaway. Lines should be routed so they do not cross or chafe.

Question 37Combination vehicle inspection and coupling/uncoupling

After uncoupling, where should the trailer air lines and electrical cord be placed?

  1. Draped over the trailer apron so they are off the ground
  2. Coiled tightly around the landing gear
  3. Left on the ground behind the trailer
  4. Secured to the trailer or tractor so they do not drag or get damaged Correct answer.

Explanation

Lines and cords should be secured in their holders or otherwise supported so they do not drag, get run over, or collect dirt. Leaving them on the ground risks damage and contamination.

Question 38Combination vehicle inspection and coupling/uncoupling

You are inspecting the fifth wheel before coupling and find the mounting bolts are loose. What should you do?

  1. Ignore it if the fifth wheel plate looks flat
  2. Couple anyway and check the bolts after the trip
  3. Tighten the bolts by hand and proceed
  4. Report the defect and do not use the vehicle until it is repaired Correct answer.

Explanation

Loose fifth wheel mounting bolts mean the coupling may not be secure, so the vehicle must be placed out of service until repaired. Hand tightening is not an adequate repair for a safety-critical mounting.

Question 39Combination vehicle inspection and coupling/uncoupling

During a walk-around inspection of a coupled combination, which check best verifies the trailer is properly secured to the tractor?

  1. The air lines are connected and the lights work
  2. The landing gear is fully raised
  3. The fifth wheel jaws are closed around the kingpin with the safety latch engaged Correct answer.
  4. The trailer apron is close to the tractor frame

Explanation

The jaws must be closed around the kingpin and the safety latch engaged to confirm a secure coupling. Lights and raised landing gear are necessary but do not prove the kingpin is locked.

Question 40Combination vehicle inspection and coupling/uncoupling

When uncoupling, why should you lower the landing gear until it firmly contacts the ground before releasing the fifth wheel?

  1. So the air lines can be disconnected safely
  2. So the kingpin can be inspected from below
  3. So the trailer is supported and does not drop when the tractor is pulled out Correct answer.
  4. So the trailer brakes release automatically

Explanation

The landing gear must carry the trailer's weight before the fifth wheel is released; otherwise the trailer drops and can damage the gear, the tractor, or injure someone. It does not affect brake release or line disconnection.

Question 41Combination vehicle inspection and coupling/uncoupling

You are about to couple to a trailer and notice the trailer is not sitting level, with one side noticeably lower. What is the most appropriate action?

  1. Back under faster to force the trailer level
  2. Raise the low side with a jack and couple
  3. Check the landing gear and trailer suspension, and correct the problem before coupling Correct answer.
  4. Couple normally; the fifth wheel will level the trailer

Explanation

An unlevel trailer may indicate landing gear or suspension damage, and coupling to it can cause the kingpin to misalign or the trailer to shift. The problem should be found and corrected before coupling.

Question 42Combination vehicle inspection and coupling/uncoupling

After connecting the air lines, you hear a steady hiss near a glad hand. What should you do?

  1. Increase engine speed to build pressure past the leak
  2. Inspect the glad hand seals and coupler, and correct the leak before driving Correct answer.
  3. Disconnect the service line and drive on the supply line only
  4. Continue; a small hiss is normal at the glad hand

Explanation

A steady hiss means an air leak at the glad hand connection, which can cause brake pressure loss. The seals and couplers should be inspected and the leak corrected before the vehicle is operated.

Question 43Combination vehicle inspection and coupling/uncoupling

What is the correct order for the final steps of coupling after the kingpin is locked and the tractor is secured?

  1. Check lights and brakes, raise landing gear, then connect air lines and cord
  2. Connect the cord only, raise the landing gear, then check brakes
  3. Connect air lines and cord, raise landing gear, then check lights and brakes Correct answer.
  4. Raise landing gear, connect air lines and electrical cord, then check lights and brakes

Explanation

After the kingpin is locked, the air lines and electrical cord are connected, the landing gear is raised, and then the lights and brakes are checked. This order ensures the trailer is supplied with air and power before the final checks.

Question 44Combination vehicle inspection and coupling/uncoupling

During a pre-trip inspection, you find the trailer's electrical cord has worn insulation exposing bare wire. What is the correct action?

  1. Tag it as a defect and have the cord replaced before operation Correct answer.
  2. Wrap it with tape and dispatch the vehicle
  3. Tuck the bare section behind the air lines
  4. Ignore it if the lights still work

Explanation

Exposed wire can short, causing a loss of trailer lights or a fire hazard, so the cord must be replaced before the vehicle is used. Tape is not a permanent repair and hiding the damage does not fix it.

Question 45Combination vehicle inspection and coupling/uncoupling

You are inspecting the coupling and find the fifth wheel plate is cracked near the mounting area. What does this require?

  1. The crack is acceptable if it is shorter than an inch
  2. The vehicle must be placed out of service until the fifth wheel is repaired or replaced Correct answer.
  3. The crack can be monitored and the vehicle used if the jaws lock
  4. The crack can be filled with weld by the driver before the trip

Explanation

A crack in the fifth wheel plate compromises its strength and can lead to coupling failure, so the vehicle must be placed out of service. Only qualified repair can return it to service.

Question 46Combination vehicle inspection and coupling/uncoupling

When backing under a trailer, at what point should you stop and get out to check alignment before the kingpin contacts the fifth wheel?

  1. Before the kingpin reaches the fifth wheel, so you can confirm height and centering Correct answer.
  2. Only if you hear a unusual noise
  3. After the trailer has been raised off the landing gear
  4. Only after the jaws have closed

Explanation

Stopping before the kingpin reaches the fifth wheel lets you confirm the trailer height and centering so the kingpin does not strike the plate or miss the jaws. Waiting until the jaws close is too late to prevent damage.

Question 47Combination vehicle inspection and coupling/uncoupling

A driver couples, performs a tug test, and the combination holds, but the trailer sits noticeably higher at the front than at the rear. What is the most likely explanation?

  1. The trailer spring brakes are still applied
  2. The trailer ABS lamp is illuminated
  3. The electrical cord is connected incorrectly
  4. The landing gear was not fully raised or the trailer is resting on it Correct answer.

Explanation

A trailer that sits high at the front after coupling is often still resting on its landing gear, meaning the gear was not fully raised or the trailer was coupled at the wrong height. The gear must be checked and raised completely.

Question 48Combination vehicle inspection and coupling/uncoupling

During uncoupling on level ground, you release the fifth wheel jaws but the tractor will not pull free. What is the most likely cause?

  1. The trailer supply line is still connected and holding the tractor Correct answer.
  2. The electrical cord is still plugged in
  3. The landing gear is too low
  4. The trailer spring brakes are released

Explanation

If the trailer supply line is still connected, air pressure and the line itself can keep the tractor from pulling free and may damage the line. All lines and the cord should be disconnected before pulling out.

Question 49Combination vehicle inspection and coupling/uncoupling

You are inspecting a coupled combination and find the trailer apron is resting on the tractor frame rather than on the fifth wheel. What does this indicate?

  1. The trailer is sitting too low or the fifth wheel is misadjusted, so the coupling is not correct Correct answer.
  2. The trailer spring brakes are set too tightly
  3. The coupling is correct and the apron is designed to carry load
  4. The electrical cord is too short

Explanation

The trailer apron should clear the tractor frame, with the load carried through the fifth wheel and kingpin. If the apron rests on the frame, the trailer height or fifth wheel adjustment is wrong and the coupling must be corrected.

Question 50Combination vehicle inspection and coupling/uncoupling

A driver must couple to a trailer whose kingpin is visibly worn with a reduced diameter. What is the correct action?

  1. Couple normally and monitor for looseness
  2. Couple and rely on the safety latch to hold it
  3. Place the trailer out of service until the kingpin is replaced Correct answer.
  4. Use extra grease to take up the clearance

Explanation

A worn kingpin can allow the jaws to slip or the trailer to separate, so the trailer must be placed out of service until the kingpin is replaced. Grease or the safety latch cannot compensate for lost material.