Free CDL Combination Vehicles Practice Test 2026

Sample questions

5 combination vehicles practice questions

Each sample shows the correct answer with a plain-language explanation. The full 54-question bank is in the practice run after you pick a state.

1. 1. To test trailer emergency brakes after charging the system:

   • ASet only the tractor parking brake
   • BOpen all shut-off valves and drive away
   • Pull out the trailer air supply control (emergency position) and gently pull with the tractor to confirm the trailer brakes hold
   • DDisconnect the service line only

   Answer: Pull out the trailer air supply control (emergency position) and gently pull with the tractor to confirm the trailer brakes hold. With the supply control in emergency, the trailer spring/emergency brakes should hold when you tug gently.

2. 2. Before coupling, inspect the fifth wheel for cracks/damage and confirm the plate is:

   • ACovered with sand for traction
   • BPainted with rust converter only
   • CDry of all grease always
   • Properly greased unless the manufacturer specifies otherwise

   Answer: Properly greased unless the manufacturer specifies otherwise. Damaged or poorly lubricated fifth wheels can bind or fail under load. Also check lock mechanism and mounting.

3. 3. When uncoupling, lower the landing gear until it:

   • ABarely touches and leaves all weight on the fifth wheel
   • Supports the trailer so the tractor can be pulled out safely
   • CIs removed from the trailer
   • DIs raised fully before chocking

   Answer: Supports the trailer so the tractor can be pulled out safely. Landing gear must take the trailer weight. Chock wheels and ensure trailer brakes hold before disconnecting air lines.

4. 4. Testing trailer service brakes usually involves:

   • AOpening rear shut-off valves on the last trailer
   • BOnly the parking brake on the tractor
   • Checking that trailer brakes apply when you use the pedal or hand valve during a low-speed check
   • DDisconnecting the battery

   Answer: Checking that trailer brakes apply when you use the pedal or hand valve during a low-speed check. Confirm trailer service braking works before entering traffic. Also test emergency brakes with the supply control.

5. 5. If both tractor and trailer have working ABS, in an emergency stop you should:

   • Brake as you normally would for control; ABS will help prevent lockup
   • BUse only the hand valve
   • CDisconnect ABS lamps first
   • DPump the brakes hard repeatedly

   Answer: Brake as you normally would for control; ABS will help prevent lockup. Brake with the force needed to stay in control. Monitor tractor and trailer and ease up if a swing starts and it is safe to do so.