Illinois CDL Combination Test (IL) 2026

4.8 out of 5 (192 votes)
80% Passing score
20 Questions
4 Mistakes allowed
Preparing for your Commercial Driver's License (CDL) combination vehicles endorsement in Illinois has never been easier with our Illinois CDL combination practice test. This thorough driving test practice encompasses all the critical areas you need to master, including coupling and uncoupling, pre-trip inspections, driving techniques, backing and maneuvering, and air brake systems. With a diverse range of multiple-choice questions, our practice permit test ensures that you are well-prepared for the DMV written test. The Illinois CDL practice test is designed with a large pool of questions and answers, providing ample opportunity for learning and retention. This variety helps in thoroughly preparing you for the Illinois rules of the road practice test, making sure you can confidently handle the written test. Each Illinois combination CDL test includes 20 questions, and you'll need to answer at least 16 correctly to pass. One of the key topics covered in the Illinois CDL combination practice test is the increased stopping distances required for combination vehicles due to their greater weight. This crucial knowledge is vital for maintaining safety on the road and handling the unique challenges presented by these larger, heavier vehicles. Our combination CDL practice test is tailored specifically to Illinois, reflecting the unique rules, regulations, and road signs of the state. This state-specific approach ensures that you are not only ready for the test but also fully prepared for real-world driving in Illinois. Accessibility is another cornerstone of our Illinois combination CDL test. Available online, it can be accessed via mobile, desktop, and mobile apps, making it convenient for you to study and practice anytime, anywhere. This flexibility allows you to fit your study sessions into your busy schedule, ensuring consistent progress towards obtaining your CDL endorsement. By utilizing our Illinois CDL combination practice test, you are taking a significant step towards securing your CDL and advancing your career as a commercial driver. Prepare with confidence, knowing you have the best resources at your fingertips.
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Sample Illinois Combination Test Questions

Question 1

After coupling, where must the fifth-wheel locking jaws be positioned on the kingpin?

  1. A Around the kingpin head
  2. B Against the upper coupler plate
  3. C Around the kingpin shank
  4. D Below the kingpin base

Correct answer: C – Around the kingpin shank

The fifth-wheel locking jaws must close around the shank of the kingpin, not its head. The driver must visually inspect the connection after coupling. The upper and lower fifth-wheel surfaces should have no visible space between them, and the release arm and safety latch must be properly secured.

Source: Illinois CDL Study Guide — § 6.5.1, “Coupling System Areas”

Question 2

How do you supply air to a connected trailer's air tanks?

  1. A Connect the blue service line to the red supply line
  2. B Pull out the trailer air-supply control
  3. C Apply the trailer hand valve continuously
  4. D Push in the trailer air-supply control

Correct answer: D – Push in the trailer air-supply control

In the Illinois guide, the trailer air-supply control on newer vehicles is a red, eight-sided knob. Pushing it in supplies air to the trailer. Pulling it out shuts off the air supply and applies the trailer emergency brakes; the valve also pops out when system pressure becomes too low.

Source: Illinois CDL Study Guide — § 6.2.3, “Trailer Air Supply Control”

Question 3

What happens if the trailer's emergency air line separates and loses pressure while driving?

  1. A Only the trailer brake lights stop working
  2. B The trailer air tanks continue charging normally
  3. C The tractor automatically increases service-brake pressure
  4. D The trailer emergency brakes apply

Correct answer: D – The trailer emergency brakes apply

Loss of pressure in the emergency or supply line causes the trailer emergency brakes to apply. This can occur if a trailer breaks away and tears the hose or if another part of the line fails. The pressure loss also causes the tractor protection valve to close and the trailer air-supply knob to pop out.

Source: Illinois CDL Study Guide — § 6.2.4, “Emergency Air Line”

Question 4

Which two practices are especially important for preventing a combination-vehicle rollover?

  1. A Place the load forward and accelerate through turns
  2. B Keep the cargo low and drive slowly around turns
  3. C Place the load toward the rear and maintain the posted speed
  4. D Place the load toward the rear and brake while turning

Correct answer: B – Keep the cargo low and drive slowly around turns

Keeping cargo close to the ground lowers the vehicle's center of gravity, reducing rollover risk. Drivers must also slow down before corners, ramps, and other turns because excessive turning speed can overturn a combination vehicle. The load should also be centered and distributed as evenly as possible.

Source: Illinois CDL Study Guide — § 6.1.1, “Rollover Risks”

Question 5

Why should glad-hand couplers and their seals be inspected and cleaned before connection?

  1. A To improve fuel economy
  2. B To reduce tire wear
  3. C To align the trailer landing gear
  4. D To help prevent air from leaking at the connection

Correct answer: D – To help prevent air from leaking at the connection

Glad hands connect the tractor's service and emergency air lines to the trailer. Their rubber seals prevent air from escaping, so the couplers and seals should be clean and undamaged before connection. The driver must also match the correct lines—normally blue for service and red for emergency or supply.

Source: Illinois CDL Study Guide — § 6.2.5, “Hose Couplers (Glad Hands)”

Question 6

When possible, you should position a trailer so you can back and turn toward the driver's side. True or false?

  1. A True
  2. B False

Correct answer: A – True

Illinois's backing guidance recommends backing and turning toward the driver's side whenever possible. This position lets the driver watch the rear of the vehicle through the side window and provides better visibility than right-side backing. Drivers should still back slowly, use both mirrors, inspect the path, and use a helper when available.

Source: Illinois CDL Study Guide — § 2.2.4, “Backing Safely”

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