If a vehicle has anti-lock brakes on just one axle, the driver will still have more control during braking than they would without any anti-lock brakes.

Will provide increased control in braking.

Will not make a difference in braking.

Will provide increased control in braking.

Will likely cause the air brakes to malfunction.

Fully-loaded rigs are more vulnerable to rolling over than empty rigs because the weight of the cargo gives the vehicles higher centers of gravity.

Are more likely to roll over than empty rigs.

Usually are very responsive to steering.

Are more likely to roll over than empty rigs.

A tractor protection valve keeps air in a tractor or truck air brake system should the trailer break away or develop a bad leak. The valve will close automatically if the pressure drops to an unsafe level.

Keeps air in a brake system if there is a bad leak.

Prevents a truck from being stolen.

Prevents a trailer from being accidentally released.

You should test the tractor protection valve by allowing the air supply to properly charge, turning off the engine, then releasing air from the system by pressing the brake pedal several times. The tractor protection valve should move into its emergency position when psi drops to an unsafe level.

Releasing air with the brake pedal.

Pulling the yellow, diamond-shaped knob.

Releasing air with the brake pedal.

If you do not know whether or not a trailer is equipped with ABS, look under the vehicle for the electronic control unit and wheel speed sensor wires coming from the back of the brakes.

Look under the trailer for wheel speed sensors coming from the back of the brakes.

Remove a tire and look for the ABS sensor on the axle.

The emergency air line controls the emergency brakes on a combination vehicle. A loss of air pressure in the emergency line will cause the emergency trailer brakes to activate.

The emergency brakes will activate.

The Anti-Lock Braking System will activate.

The service air line will activate.

The emergency brakes will activate.

Combination Vehicles Practice Test | Iowa 2024 #2

Train for FREE online with our Iowa CDL combination vehicle test. The official exam test consists of several obligatory parts, with all of them checking your knowledge of different blocks of road rules. If you need to obtain a IA combination license in 2024, practice as much as possible. Free sample tests published on our website will help you check and improve your knowledge and boost your grades. Please bear in mind that DMV requirements for issuing a combination license may vary from state to state.

Number of Question 20

Passing Score 16

Number of Tests 20

Combination Vehicles Practice Test | Iowa 2024 #2

1 . Having anti-lock brakes on only one axle:

2 . Fully-loaded rigs:

3 . A trailer that is too high:

4 . A tractor protection valve:

5 . A driver should test the tractor protection valve by:

6 . If unsure if a trailer has an Anti-Lock Braking System (ABS), you can:

7 . If the emergency air line loses pressure:

Search the best driving school in your neighbourhood