Iowa CDL — Air Brakes Practice Test

The Iowa CDL — Air Brakes knowledge test has ~25 questions; you need ~20 correct (80%) to pass.

Or take one of 10 full-length practice tests

25 questions · pass with 20 correct. You get instant feedback and an explanation after every answer.

Choose your level

The full-length test, with feedback and an explanation after every answer.

Iowa CDL — Air Brakes practice tests

10 full-length practice tests, each with 25 questions and a pass mark of 20, like the real test. You see the answers and explanations after you grade.

Test 1
25 questions · pass with 20
On Iowa's inspection test, you check the brake lines and hoses at the steering axle. According to the manual, what may a loss of air pressure in those lines cause?
Test 2
25 questions · pass with 20
Your straight truck has ABS on all axles, but its yellow ABS lamp has stayed lit all day. A car stops suddenly ahead and you must brake hard. Which approach fits the manual?
Test 3
25 questions · pass with 20
Four drivers each report one result from their final air brake checks. Which result is within what the manual expects?
Test 4
25 questions · pass with 20
You usually drive a medium truck with hydraulic brakes, but today you're in an air-braked truck at the same speed. Even if you react just as quickly, how should this change the room you leave ahead?
Test 5
25 questions · pass with 20
While you're driving, a mechanical arm suddenly swings down into your view. What has happened?
Test 6
25 questions · pass with 20
The manual says to set the parking brakes whenever you park, with two exceptions. Which pair of conditions are they?
Test 7
25 questions · pass with 20
Automatic slack adjusters are meant to keep brakes in adjustment, yet one of yours is past its legal pushrod stroke limit. Which explanation does the manual NOT offer for that?
Test 8
25 questions · pass with 20
In Iowa's air brake check, you have just finished the leakage test. What should you do about the engine before starting the low air warning test?
Test 9
25 questions · pass with 20
Four different rigs each lose 2.5 psi in one minute during their pre-trip air leakage checks, all with the engine off. Which rig should stay parked until the leak is found and fixed?
Test 10
25 questions · pass with 20
On Iowa's inspection test, you check the air lines between the power unit and an air-braked trailer. What does the manual say a low air condition can do to the trailer?