Iowa Combination Vehicles CDL Practice Test
Below are 25 exam-style questions for the Iowa Combination Vehicles CDL knowledge test, modeled on the FMCSA-aligned content used by the Iowa Department of Transportation. 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 You will notice immediately because trailer brakes will not work properly
- B The horn will sound
- C The trailer brakes will be locked on
- D Nothing will happen
- A Pump the brakes 10 times
- B Drive away immediately
- C Drain the wet tank
- D Charge the trailer brakes by setting the trailer air supply control
- A Tied with rope
- B Locked and the safety latch in place after coupling
- C Released and visible after coupling
- D Removed before driving
- A Should be replaced when worn beyond manufacturer specs
- B Make the truck quieter
- C Are normal until the lining is gone
- D Only need attention every 5 years
- A Before, during, and after coupling
- B Only at the start of the day
- C Every 3 hours
- D Only at the destination
- A Back at full speed
- B GOAL — Get Out And Look — and walk around the trailer first
- C Use only mirrors
- D Have the dispatcher in the cab
- A Drive wheels never lock
- B Brake balance is irrelevant
- C ABS prevents jackknife in all cases
- D Trailer wheels lock more often than drive wheels in panic stops
- A Lane positioning at intersections
- B The trailer following the same path as the tractor in a straight line
- C The fuel mileage
- D Cargo placement
- A Is used to convert a semitrailer into a full trailer for towing in combination
- B Is part of the tractor
- C Replaces the fifth wheel on the tractor
- D Is used only when triple-towing
- A Backing too fast
- B Coupling with the trailer too high
- C Failure to grease
- D All of the above
- A They are heavier and longer
- B They take more skill to back, couple, and uncouple
- C All of the above
- D They have a higher rollover risk
- A Lower landing gear, disconnect lines, release fifth wheel, pull tractor away
- B No specific order is required
- C Pull tractor away first, then disconnect lines
- D Release fifth wheel first, then connect lines
- A Hold the vehicle when parking
- B Test the trailer brakes
- C Both for parking and to prevent jackknife
- D Apply trailer brakes momentarily
- A Lowered to the ground while driving
- B Fully raised before driving
- C Always halfway extended
- D Disconnected before driving
- A Cargo placement
- B Cuts, abrasions, and worn seals
- C Loose lug nuts only
- D Engine oil leaks
- A You are driving slowly
- B The drive wheels lock and the trailer pushes the tractor sideways
- C The brakes are released gently
- D The trailer wheels lock briefly
- A Leave the gear up
- B Lower the landing gear all the way until firmly on the ground, then a few extra cranks
- C Use blocks instead
- D Raise the gear partway
- A Brake adjustment levers
- B Electrical connectors
- C Manual transmission shifters
- D Coupling devices for connecting tractor air lines to the trailer
- A Back to the left whenever possible because you can see better
- B Back as fast as practical
- C Back without using mirrors
- D Always back to the right
- A No off-tracking
- B Wheel damage
- C Off-tracking — the trailer wheels follow a tighter arc than the tractor
- D Brake fade
- A Stopping distances increase and the trailer can swing
- B Steering becomes easier
- C Stopping distances are normal
- D No effect on safety
- A Connect air emergency line first, then service line, then electrical (or per company policy) — verify with brake check
- B Connect only air; electrical is optional
- C Connect electrical first, then air
- D Connect any line first; order doesn't matter
- A Spin out
- B Stop suddenly
- C Roll over before sliding
- D Lose engine power
- A Rust on the cab
- B Engine damage
- C Tire wear only
- D The trailer to come uncoupled
- A Empty
- B Properly chocked
- C Loaded
- D Too high — it can damage the kingpin or skip over the fifth wheel
Study tips for the Iowa Combination Vehicles exam
The Combination Vehicles portion of the Iowa CDL exam is graded out of the bank of questions the Iowa Department of Transportation draws from each year. While the exact bank is not published, every question is sourced from the Combination Vehicles chapter of the Iowa 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 Iowa 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 Iowa Department of Transportation 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 Iowa 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 Iowa 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 Iowa Department of Transportation office.
Already comfortable with this endorsement? Drill another: IA General Knowledge · IA Air Brakes · IA Hazardous Materials · IA Passenger · IA School Bus · IA Tank Vehicle · IA Doubles / Triples
New to the CDL process in Iowa? Read How to apply for a CDL in Iowa for the document checklist and step-by-step timeline.