Commercial driver’s license (CDL) knowledge tests · California DMV
Inspecting a Combination Vehicle
Questions and answers
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Which procedure do you use to inspect a combination vehicle?
The 7-step inspection procedure from Section 2, plus the additional combination checks
The 7-step procedure applies, and a combination vehicle has more things to inspect than a single vehicle.
Section 6 · 6.5 – Inspecting a Combination ↗ -
During the walk around, where must the locking jaws of the fifth-wheel be?
Around the shank of the kingpin, not the head
The jaws must be closed around the shank of the kingpin.
Section 6 · Coupling System Areas ↗ -
Which of these is a defect in the lower fifth-wheel?
Visible space between the upper and lower fifth-wheel
There must be no visible space between the upper and lower fifth-wheel.
Section 6 · Coupling System Areas ↗ -
What do you check about the release arm of the fifth-wheel?
It is properly seated and the safety latch or lock is engaged
The release arm must be seated with the safety latch or lock engaged.
Section 6 · Coupling System Areas ↗ -
What do you check on the upper fifth-wheel?
The glide plate is securely mounted to the trailer frame and the kingpin is not damaged
The upper fifth-wheel check covers the glide plate mounting and the kingpin.
Section 6 · Coupling System Areas ↗ -
How should the air lines to the trailer be secured?
With enough slack for turns
Air lines must be properly connected to the glad hands, free of leaks, and secured with enough slack for turns.
Section 6 · Coupling System Areas ↗ -
What do you check about the electrical cord to the trailer?
It is firmly plugged in and secured
The electrical cord must be firmly plugged in and secured.
Section 6 · Coupling System Areas ↗ -
What must be true of the locking pins on a sliding fifth-wheel?
All locking pins are present and locked in place
Every locking pin must be present and locked.
Section 6 · Coupling System Areas ↗ -
How far forward may a sliding fifth-wheel be set?
Not so far that the tractor frame hits the landing gear or the cab hits the trailer in turns
A fifth-wheel set too far forward lets the tractor frame strike the landing gear or the cab strike the trailer during turns.
Section 6 · Coupling System Areas ↗ -
The sliding fifth-wheel is air powered. What do you check?
That there are no air leaks
An air powered slide must have no air leaks.
Section 6 · Coupling System Areas ↗ -
In what position must the landing gear be during the walk around inspection?
Fully raised
The landing gear must be fully raised, with no missing parts and not bent or damaged.
Section 6 · Landing Gear ↗ -
What do you check about the landing gear crank handle?
It is in place and secured
The crank handle must be in place and secured.
Section 6 · Landing Gear ↗ -
The landing gear is power operated. What do you check?
That there are no air or hydraulic leaks
Power operated landing gear must have no air or hydraulic leaks.
Section 6 · Landing Gear ↗ -
To check that air flows to all the trailers, which control do you push in first?
The red “trailer air supply” knob
After normal air pressure is reached, pushing in the red knob supplies air to the emergency (supply) lines.
Section 6 · 6.5.2 – Combination Vehicle Brake Check ↗ -
In the air flow check, what do you use to provide air to the service line?
The trailer handbrake
The trailer handbrake puts air in the service line for the check.
Section 6 · 6.5.2 – Combination Vehicle Brake Check ↗ -
In the air flow check, which valve do you open first at the rear of the rig?
The emergency line shut-off valve at the rear of the last trailer
Opening the emergency line valve at the rear of the last trailer should let you hear air escaping.
Section 6 · 6.5.2 – Combination Vehicle Brake Check ↗ -
You open the emergency line shut-off valve at the rear of the last trailer and hear air escaping. What does that show?
The entire system is charged
Escaping air at the back of the last trailer shows that air has reached the whole system.
Section 6 · 6.5.2 – Combination Vehicle Brake Check ↗ -
You do not hear air escaping from both lines at the rear of the last trailer. What do you check?
That the shut-off valves on the trailers and dollies are in the open position
You must have air all the way to the back for all the brakes to work.
Section 6 · 6.5.2 – Combination Vehicle Brake Check ↗ -
How do you test the tractor protection valve?
Charge the trailer air system, shut the engine off, and step on and off the brake pedal several times
Pumping the pedal lowers tank pressure until the trailer air supply control pops out.
Section 6 · 6.5.2 – Combination Vehicle Brake Check ↗ -
In the tractor protection valve test, when should the trailer air supply control pop out?
When air pressure falls into the manufacturer’s range, usually 20 to 45 psi
The control should pop out, or go from normal to emergency, usually within 20 to 45 psi.
Section 6 · 6.5.2 – Combination Vehicle Brake Check ↗ -
What could happen if the tractor protection valve does not work right?
An air hose or trailer brake leak could drain all the air from the tractor
Losing all the tractor’s air would bring on the emergency brakes, with possible loss of control.
Section 6 · 6.5.2 – Combination Vehicle Brake Check ↗ -
How do you test the trailer emergency brakes?
Charge the trailer system, check that the trailer rolls freely, stop, pull out the trailer air supply control, and pull gently on the trailer
With the air supply control pulled out, a gentle pull with the tractor shows that the trailer emergency brakes are on.
Section 6 · 6.5.2 – Combination Vehicle Brake Check ↗ -
How do you test the trailer service brakes?
Release the parking brakes, move forward slowly, and apply the trailer brakes with the hand control
You should feel the brakes come on, which shows the trailer brakes are connected and working.
Section 6 · 6.5.2 – Combination Vehicle Brake Check ↗ -
The trailer brakes are tested with the hand valve. How are they controlled in normal operation?
With the foot pedal, which applies air to the service brakes at all wheels
The hand valve is for testing. Normal braking is done with the foot pedal.
Section 6 · 6.5.2 – Combination Vehicle Brake Check ↗
Questions and answers by topic
- Licenses, endorsements and tests105
- Disqualifications and state rules110
- Vehicle inspection80
- Basic control and shifting gears47
- Seeing and communicating46
- Controlling your speed62
- Managing space40
- Seeing hazards49
- Distracted and Aggressive Driving71
- Night, Fog, Winter and Hot Weather124
- Railroad Crossings and Mountain Driving65
- Emergencies, ABS and Skids102
- Accident Procedures and Fires49
- Alcohol, Drugs and Illness41
- Hazardous Materials Rules for All Drivers42
- Transporting Cargo Safely79
- Bus Inspection, Loading and Hazardous Materials74
- Driving a Bus: Stops, Crossings and Prohibited Practices56
- Air Brake Parts: Compressor, Tanks and Foundation Brakes52
- Warnings, Spring Brakes, ABS and Dual Systems59
- Inspecting Air Brake Systems61
- Using Air Brakes51
- Driving Combination Vehicles Safely50
- Combination Vehicle Air Brakes and ABS59
- Coupling and Uncoupling63
- Pulling Double and Triple Trailers16
- Coupling, Inspecting and Brake Checks for Doubles34
- Tank Vehicles62
- HazMat basics and who does what48
- Hazard classes, labels and lists64
- Shipping papers and package markings49
- Placards and placard tables40
- Loading and unloading HazMat58
- Bulk packaging and tanks30
- HazMat driving and parking rules72
- HazMat emergencies and reporting60
- Danger zones and mirrors34
- Loading and unloading students47
- Emergency exit and evacuation34
- Railroad-highway crossings40
- Student management, ABS and special situations47