Illinois Combination Vehicles CDL Practice Test
Below are 25 exam-style questions for the Illinois Combination Vehicles CDL knowledge test, modeled on the FMCSA-aligned content used by the Illinois Secretary of State. Try to answer each question on your own before reading the answer key directly under it. The questions and answer choices are shuffled deterministically per state and endorsement, so the order will stay the same on repeat visits — that lets you genuinely measure your improvement.
- A Use the shoulder
- B Stay in the right lane and swing the front of the tractor wide enough to clear the curb without inviting cars to pass on the right
- C Turn from the left lane
- D Stop traffic by signaling left
- A Trailer sway in crosswinds
- B All of the above
- C Off-tracking on right turns
- D Reduced visibility along the trailer
- A Square, white, marked CHARGE
- B Triangular, green, marked SERVICE
- C Octagonal, red, marked TRAILER AIR SUPPLY
- D Round, blue, marked TRACTOR
- A Lower landing gear, disconnect lines, release fifth wheel, pull tractor away
- B Pull tractor away first, then disconnect lines
- C No specific order is required
- D Release fifth wheel first, then connect lines
- A Electrical power for trailer lights and ABS
- B Hydraulic fluid
- C Fuel
- D Air for the brakes
- A By pushing in the red trailer-air-supply valve
- B By the trailer hand valve
- C By setting the red trailer-air-supply valve
- D By pulling out the red trailer-air-supply valve
- A You are driving slowly
- B The drive wheels lock and the trailer pushes the tractor sideways
- C The trailer wheels lock briefly
- D The brakes are released gently
- A Apply trailer brakes momentarily
- B Hold the vehicle when parking
- C Both for parking and to prevent jackknife
- D Test the trailer brakes
- A Set only the tractor parking brake
- B Set both tractor and trailer parking brakes
- C Use the trailer hand valve
- D Leave the engine running with the brakes off
- A Stop on the tracks if traffic ahead slows
- B Honk and accelerate
- C Shift in the middle of the track
- D Cross in a low gear without shifting
- A Disconnected before driving
- B Always halfway extended
- C Fully raised before driving
- D Lowered to the ground while driving
- A Replaces the fifth wheel on the tractor
- B Is used to convert a semitrailer into a full trailer for towing in combination
- C Is part of the tractor
- D Is used only when triple-towing
- A Cargo placement
- B Loose lug nuts only
- C Cuts, abrasions, and worn seals
- D Engine oil leaks
- A Every 3 hours
- B Before, during, and after coupling
- C Only at the destination
- D Only at the start of the day
- A Cargo placement
- B The fuel mileage
- C The trailer following the same path as the tractor in a straight line
- D Lane positioning at intersections
- A The trailer to come uncoupled
- B Tire wear only
- C Engine damage
- D Rust on the cab
- A Disconnect the air supply
- B Apply the trailer hand valve harder
- C Release the brakes to allow the trailer wheels to roll again, then steer
- D Accelerate
- A Last
- B Either position is fine
- C Loaded last
- D First (closest to the tractor)
- A Properly chocked
- B Loaded
- C Too high — it can damage the kingpin or skip over the fifth wheel
- D Empty
- A Back without using mirrors
- B Back to the left whenever possible because you can see better
- C Back as fast as practical
- D Always back to the right
- A Maximum legal height
- B Whatever height it happens to be
- C A height that requires the tractor to drop down to fit
- D A height where the tractor will lift the trailer slightly when backing under
- A It can damage the cab and the trailer (cab corner crush)
- B It is the standard procedure
- C It is illegal in some states
- D It is fine if you are careful
- A Driver fatigue
- B Cargo placement
- C Air leakage in the supply line, low pressure, or a brake-balance issue
- D Engine wear
- A Need a mechanic to find
- B Can be detected during pre-trip inspection by visual and pressure checks
- C Are caused by low fuel
- D Show up only at high speed
- A The drive wheels lose traction and the tractor begins to slide
- B The trailer is too heavy
- C The tractor parking brake fails
- D The fifth wheel disengages
Study tips for the Illinois Combination Vehicles exam
The Combination Vehicles portion of the Illinois CDL exam is graded out of the bank of questions the Illinois Secretary of State draws from each year. While the exact bank is not published, every question is sourced from the Combination Vehicles chapter of the Illinois CDL handbook, which itself is derived from the FMCSA Model Commercial Driver's License Manual. That means studying our practice tests, reading the corresponding handbook chapter, and re-reading the parts you got wrong is genuinely the most efficient route to a first-time pass.
Most successful applicants follow a simple cycle: take the practice test cold, write down every question you missed, open the matching chapter of the official Illinois handbook, re-read the section that contains the right answer, then re-take the practice test 24 to 48 hours later. The 24-hour delay matters — sleep is when your brain commits new information to long-term memory, and CDL knowledge questions reward that kind of consolidated learning rather than cramming.
Pay particular attention to questions that include qualifier words like always, never, only, primary, or most. CDL test writers love to flip the right answer with a single qualifier. When two answer choices look almost identical, pay attention to the verb (is it must, should, or may?) and to any numbers (14 days, 100 air miles, 8 hours, 70/8 split). On endorsement tests in particular, watch for trick framing where a true statement about a different endorsement is offered as the "correct" answer to a question that is actually about Combination Vehicles.
Test-day logistics matter too. Bring photo ID, your Social Security card or birth certificate, your medical examiner's certificate (DOT card), and proof of state residency if you haven't already submitted those documents. The Illinois Secretary of State will not let you sit for the knowledge exam without your documentation, and most offices charge an additional fee for re-attempts. Arrive early — the wait at most CDL testing offices runs 30 to 60 minutes — and silence your phone before the exam begins.
Finally, keep your General Knowledge fundamentals sharp even when you're focused on the Combination Vehicles exam. Many states administer multiple knowledge tests in a single sitting, and questions on weight definitions (GVWR, GCWR, GAWR), stopping distance, and the pre-trip inspection routine show up across endorsements. If you're unsure on the basics, sit a fresh Illinois General Knowledge practice test before scheduling the real exam.
Next steps
Missed more than four questions? Re-read the Combination Vehicles study guide and the matching chapter in the official Illinois CDL handbook. Then come back and re-take the test. Once you can score 22 of 25 or higher on three runs in a row, you're in good shape to schedule the real exam at your local Illinois Secretary of State office.
Already comfortable with this endorsement? Drill another: IL General Knowledge · IL Air Brakes · IL Hazardous Materials · IL Passenger · IL School Bus · IL Tank Vehicle · IL Doubles / Triples
New to the CDL process in Illinois? Read How to apply for a CDL in Illinois for the document checklist and step-by-step timeline.