How is the tractor-trailer connection initially tested after the kingpin locks?
Correct answer: With supports slightly raised, gently tug against locked trailer brakes
A gentle pull against the locked trailer brakes is an initial coupling check, not complete proof. Secure the vehicle and also visually check that the fifth-wheel plates meet and the jaws are locked around the kingpin shank before driving.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.4.1 Coupling Tractor-Semitrailers — Step 11 Check Connection for Security; Steps 12–13, printed 6-10 (physical PDF page 116) ↗
Where should the fifth-wheel locking jaws be after proper coupling?
Correct answer: Around the shank of the kingpin
Secure the vehicle before looking underneath. Check that the jaws have closed around the kingpin shank, not its head, and that there is no gap between the upper and lower fifth-wheel plates. Also inspect the locking lever and safety latch.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.5.1 Coupling System Areas and Figure 6.11, printed 6-15 (physical PDF page 121); secure-vehicle procedure at 6.4.1 steps 12–13, printed 6-10 / physical 116 ↗
Before driving a coupled tractor-semitrailer, how far should the landing gear be raised?
Correct answer: Fully raised with the crank secured
Partly raised gear can strike tracks or road objects and must be fully stowed.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.4.1 Coupling Tractor-Semitrailers — Step 15 Raise Front Trailer Supports, printed 6-10 (physical PDF page 116) ↗
While uncoupling a tractor-semitrailer, why stop with the fifth wheel clear but the tractor frame still under the trailer?
Correct answer: Support the trailer if its landing gear fails
Keeping the tractor frame under the trailer provides temporary support while the landing gear is checked.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.4.2 Uncoupling Tractor-Semitrailers — Step 7 Pull Tractor Partially Clear of Trailer, printed 6-11 (physical PDF page 117) ↗
On a combination equipped with a trailer hand valve, how are the trailer service brakes checked before normal operation?
Correct answer: Move slowly and test with the trailer hand valve
Check normal air pressure, release the parking brakes and move forward slowly in a safe test area. Apply the trailer hand control, if equipped, and feel the trailer brakes engage. During normal driving use the foot pedal to control service brakes at all wheels.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.5.2 Combination Vehicle Brake Check — Test Trailer Service Brakes, printed 6-16 (physical PDF page 122) ↗
You find dirt on a glad-hand coupling and its rubber seal before connecting a trailer. What should you do?
Correct answer: Clean the coupler and seal before making the connection
Clean couplers and seals before connecting them. The rubber seal prevents air from escaping, and keeping contamination out protects the air system.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.2.5 Hose Couplers (Glad Hands), printed 6-6 (physical PDF page 112) ↗
After disconnecting a trailer, where should the tractor’s air-line couplers be attached if dummy couplers are provided?
Correct answer: To the dummy couplers to keep dirt and water out
Dummy or dead-end couplers protect unused air lines from water and dirt. Use them when the hoses are not connected to a trailer.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.2.5 Hose Couplers (Glad Hands), printed 6-6 (physical PDF page 112) ↗
When you press the foot brake, what determines how much pressure the relay valves send from the trailer reservoirs to its brakes?
Correct answer: The pressure in the service line
Service-line pressure communicates the braking demand to the relay valves. The trailer’s own reservoirs supply the air sent to its brakes.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.2.6 Trailer Air Tanks, printed 6-7 (physical PDF page 113) ↗
A major trailer service-line leak may become obvious only when you apply the brakes. What can happen then?
Correct answer: Air pressure can fall rapidly and eventually apply the trailer emergency brakes
A service-line leak may not be apparent until braking pressurizes that line. The resulting air loss can rapidly lower tank pressure; at sufficiently low pressure, trailer emergency brakes can apply.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.2.8 Trailer Service, Parking and Emergency Brakes, printed 6-7 (physical PDF page 113) ↗
A tractor-trailer has ABS on the trailer but not on the tractor. Which statement is correct?
Correct answer: Trailer ABS still helps, but the tractor can still lose control under braking
Trailer ABS can reduce trailer swing, but it cannot prevent tractor wheel lock. Use only the force needed to stop safely. If steering control is lost or a tractor jackknife starts, ease off the brakes if safe until control returns. ABS does not justify a shorter following gap.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.3.2 Braking with ABS, printed 6-8 (physical PDF page 114) ↗
Does an automatic drain eliminate the handbook’s advice to check trailer air tanks for accumulated moisture?
Correct answer: No; open the drains to check for remaining moisture
The handbook says to drain each trailer air tank daily and still open drains to check tanks with automatic drains. Water and oil accumulation can interfere with correct brake operation.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.2.6 Trailer Air Tanks, printed 6-7 (physical PDF page 113) ↗
Before backing a tractor under a trailer, what must prevent the trailer from rolling?
Correct answer: Applied spring brakes or appropriate wheel chocks
Coupling forces can move an unsecured trailer. Check the area and its securement first.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.4.1 Coupling Tractor-Semitrailers — Step 2 Inspect Area and Chock Wheels, printed 6-9 (physical PDF page 115) ↗
Why should the tractor be straight in front of the trailer before coupling?
Correct answer: An angled approach can damage the landing gear
Align the units rather than use the tractor to force the trailer sideways.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.4.1 Coupling Tractor-Semitrailers — Step 3 Position Tractor, printed 6-9 (physical PDF page 115) ↗
How should air lines be arranged before you finish backing under the trailer?
Correct answer: Supported clear of crushing and snagging points
Line support must protect the connections during coupling and later movement.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.4.1 Coupling Tractor-Semitrailers — Step 7 Connect Air Lines to Trailer, printed 6-9 (physical PDF page 115) ↗
What reverse gear and speed are appropriate for the final coupling movement?
Correct answer: Lowest reverse gear at a slow, controlled speed
Avoid striking the kingpin hard while completing the connection.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.4.1 Coupling Tractor-Semitrailers — Step 10 Back Under Trailer, printed 6-10 (physical PDF page 116) ↗
Before going underneath to inspect the coupling, how should you secure the tractor?
Correct answer: Parking brakes on, transmission neutral, engine off, and key with you
Prevent someone moving the rig while you inspect underneath.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.4.1 Coupling Tractor-Semitrailers — Step 12 Secure Vehicle, printed 6-10 (physical PDF page 116) ↗
You see a gap between the trailer’s upper plate and the fifth-wheel plate after coupling. What should you do?
Correct answer: Do not drive until the coupling problem is corrected
A gap can mean the kingpin is resting above the jaws rather than being correctly locked.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.4.1 Coupling Tractor-Semitrailers — Step 13 Inspect Coupling, printed 6-10 (physical PDF page 116) ↗
Besides checking the jaws around the kingpin, which locking parts need inspection?
Correct answer: The locking lever and its safety latch
Verify the complete locking mechanism rather than relying on a tug test alone.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.4.1 Coupling Tractor-Semitrailers — Step 13 Inspect Coupling, printed 6-10 (physical PDF page 116) ↗
Once the trailer’s weight rests on the tractor, which clearances must you check?
Correct answer: Tractor frame to landing gear and tractor tires to trailer nose
Turning or suspension movement must not cause contact between the units.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.4.1 Coupling Tractor-Semitrailers — Step 15 Raise Front Trailer Supports, printed 6-10 (physical PDF page 116) ↗
Before uncoupling a loaded trailer, what must you know about the parking surface?
Correct answer: It can support the trailer and landing gear
Landing gear can sink or collapse on an unsuitable surface.
Source: Pennsylvania Commercial Driver's License Manual PUB 223 (6-26), section 6.4.2 Uncoupling Tractor-Semitrailers — Step 1 Position Rig, printed 6-11 (physical PDF page 117) ↗
