CSLB General Building (B) Trade Practice Test
Frequently asked questions
How many CDL Combination Vehicles practice questions are here?+
A full bank of original CDL Combination Vehicles practice questions across the official content areas, weighted like the real exam, with explanations. Free, no signup.
What is the CDL Combination Vehicles exam like?+
About 60 questions. Practice by topic here, then take the full timed mock exam to gauge readiness.
Are these the real exam questions?+
No. Every question is 100% original, written from public primary sources with explanations. We never copy real exam questions or paid prep material.
Can I study in Chinese or Spanish?+
PrepPass practice is in English, 中文 and Español. The official exam is in English — switch the question language to English any time to rehearse the exact terminology you'll see on test day.
Sample practice questions
A few real questions from this free bank, with full explanations. Use the practice tool above for the whole set.
- 1. Coupling & Uncoupling
Before backing a tractor under a trailer, where should the trailer be positioned relative to the fifth wheel?
- a.Slightly higher than the fifth wheel so it can slide up as you back
- b.Low enough that the trailer is raised slightly by the tractor as you back under it
- c.At the exact same height so no lifting occurs
- d.Below the frame rails so the kingpin drops in freely
Answer: b
Explanation: The trailer should be low enough that it is raised slightly when the tractor backs under it. This ensures the fifth wheel makes solid contact and the kingpin seats properly. If the trailer is too low the tractor may hit and damage the nose; too high and it can miss the fifth wheel.
- 2. Coupling & Uncoupling
When should the locking jaws be closed around the kingpin?
- a.Around the top head of the kingpin
- b.Loosely, so the trailer can pivot freely
- c.Around the shank of the kingpin, with no gap between the upper and lower fifth wheel plates
- d.Only after the landing gear is fully lowered
Answer: c
Explanation: The locking jaws must close around the shank of the kingpin, and there should be no space between the upper and lower fifth wheel plates. If the jaws close on the head of the kingpin, the coupling can come apart. A gap between the plates indicates a bad coupling that must be corrected before driving.
- 3. Coupling & Uncoupling
When uncoupling, what does pulling the fifth wheel release handle to the open position do?
- a.Unlocks the fifth wheel locking jaws so the kingpin can slide out
- b.Raises the landing gear
- c.Supplies air to the trailer
- d.Locks the trailer brakes
Answer: a
Explanation: Pulling the release handle to the open position unlocks the fifth wheel jaws so the trailer kingpin can separate as the tractor pulls forward. You should only do this after the landing gear supports the trailer and the trailer brakes are set. Chock the wheels if the trailer has no spring brakes.
- 4. Coupling & Uncoupling
Before coupling, why should you inspect the area around and under the trailer?
- a.To count the tires
- b.To look for a place to park the tractor
- c.To check for people, obstacles, or objects and confirm the trailer wheels are chocked or brakes set
- d.To adjust the mirrors
Answer: c
Explanation: You should walk around and check under the trailer for people, pets, or obstacles before backing under it. Confirm the trailer wheels are chocked or the trailer brakes are set so it cannot move. This inspection prevents injury and equipment damage during coupling.
- 5. Inspection
When inspecting the coupling system of a combination vehicle, what should you check about the fifth wheel mounting?
- a.That mounting bolts and brackets are secure and none are missing or broken
- b.That it is painted to match the cab
- c.That the fifth wheel is completely dry
- d.That it is tilted forward
Answer: a
Explanation: During inspection you must check that the fifth wheel is securely mounted, with no missing or broken mounting bolts, brackets, or welds. A loose or cracked fifth wheel mount can fail under load. This is a critical part of the combination vehicle coupling inspection.
- 6. Inspection
When checking the trailer service brakes during a combination vehicle inspection, what should you do?
- a.Only look at the brake lights
- b.Rev the engine and listen
- c.Charge the system, release the parking brakes, move slowly, and apply the brake pedal to confirm the vehicle stops and does not pull to one side
- d.Disconnect the glad hands
Answer: c
Explanation: To check service brakes, charge the air system, release the parking brakes, roll forward slowly, and press the brake pedal. The vehicle should stop straight without pulling to one side and without unusual feel. Pulling or a delayed stop can indicate a brake problem on the tractor or trailer.
- 7. Inspection
When inspecting the trailer's suspension system, what should you look for?
- a.Cracked or broken spring hangers, missing or broken leaves, and loose or damaged air suspension parts
- b.Only the tire pressure
- c.Only the mud flaps
- d.The color of the frame
Answer: a
Explanation: You should inspect the trailer suspension for cracked or broken spring hangers, missing or shifted spring leaves, and any loose or leaking air suspension components. Suspension failures can affect handling and load stability. Also check U-bolts, shock absorbers, and mounting hardware.
- 8. Inspection
When you check air lines during a combination inspection, which lines are you connecting and inspecting?
- a.Only the fuel line
- b.Only the electrical line
- c.The service (blue) air line and the emergency (red) air line
- d.The coolant and oil lines
Answer: c
Explanation: On a combination vehicle you inspect and connect the service air line, often blue, and the emergency air line, often red. The service line carries air for normal braking, and the emergency line supplies the trailer reservoir and controls the spring brakes. Both must be secure and leak-free.
- 9. Driving Safely
What causes a trailer to swing out and jackknife (trailer skid)?
- a.The trailer wheels lock up and the trailer slides sideways, often from hard braking or braking in a turn
- b.The trailer wheels have too much traction
- c.The kingpin is greased
- d.The load is too low
Answer: a
Explanation: A trailer jackknife happens when the trailer wheels lock and lose traction, causing the trailer to slide sideways and swing around toward the tractor. Hard braking, braking in a curve, or slippery roads can trigger it. Smooth braking and keeping traction on the trailer wheels help prevent it.
- 10. Driving Safely
How does the trailer respond to steering inputs compared to the tractor, and why does this matter?
- a.The trailer responds instantly to steering
- b.The trailer never moves independently
- c.The trailer lags behind and can swing or off-track, so drivers must plan turns and lane changes with extra room
- d.The trailer steers itself
Answer: c
Explanation: The trailer follows and reacts more slowly than the tractor, lagging behind in turns and lane changes and off-tracking to the inside. This means drivers must plan turns wide and check that the trailer clears obstacles and other lanes. Abrupt steering can make the trailer swing dangerously.