California CDL Combination Vehicles Test - 30 Practice Questions & Answer Key (2026)

If you're going for a Class A in California, you can't skip this one. The Combination Vehicles test is the section that decides whether you can legally pull a trailer with that tractor. No combination test, no Class A. It's that simple.

This guide gives you 30 practice questions straight out of Section 6 of the California Commercial Driver Handbook (DL 650). The DMV writes its real exam from the same source, so if you can answer these cold, you walk in ready. Coupling, uncoupling, fifth wheel checks, kingpin, off-tracking, trailer brake fade - it's all in here.

The answer key sits at the bottom with the handbook section for every answer so you can go check the book yourself. That's how you actually learn this stuff instead of just memorizing.

Who needs the combination test?

Only Class A applicants. If you're going for Class B (straight truck) or Class C (passenger van, small hazmat), you skip this one. But Class A is the most useful license out there - it lets you drive everything from a 18-wheeler down to a pickup truck. That's why most people who go through CDL school chase the A.

Here's how the tests stack up:

The combination test is 20 questions on the real DMV exam. You need 80% to pass (16 correct out of 20). Source: California Commercial Driver Handbook (DL 650), Section 6.

If you want a full breakdown of every CDL test you'll face, jump to our California CDL practice test 2026 guide.

What the combination test actually covers

Six big topics. Memorize these and you've got the test:

1. Coupling and uncoupling - the 11-step procedure for hooking up a trailer
2. Fifth wheel and kingpin - what locks the trailer to the tractor and how to inspect it
3. Trailer air brakes and emergency systems - how the trailer stops if it breaks loose
4. Off-tracking and turning - why the trailer cuts inside on turns and how to compensate
5. Backing combination vehicles - the steering wheel goes the opposite way, and that's where new drivers panic
6. Inspection points unique to combos - landing gear, glad hands, safety chains, mud flaps

Real talk: The combination test is mostly common-sense mechanical stuff once you've actually coupled a trailer twice. If you've only read about it in a book, the questions about pin height and landing gear feel abstract. Get in a yard and hook a trailer up before exam day if you possibly can. One real coupling beats fifty practice questions.

30 Practice Questions

Coupling & Uncoupling (Q1-Q10)

1. Before backing under a trailer, the fifth wheel jaws should be: A) Closed B) Open C) Greased only D) Removed

2. The kingpin connects the trailer to: A) The trailer wheels B) The fifth wheel on the tractor C) The air brake lines D) The landing gear

3. When coupling, you should back under the trailer: A) At full speed B) Slowly, in a straight line C) From the side D) Only after raising the landing gear

4. After coupling, you should test the connection by: A) Honking the horn B) Pulling forward gently in low gear with the trailer brakes locked C) Walking around the trailer D) Looking at the gauges

5. The trailer height before coupling should be: A) Higher than the fifth wheel B) Lower than the fifth wheel C) Slightly lower so the tractor lifts it slightly D) Even with the ground

6. The fifth wheel should be inspected for: A) Cracks, missing parts, and proper lubrication B) Color only C) Paint matching D) Tire pressure

7. Before uncoupling, you should: A) Lower the landing gear until it just touches the ground B) Lower the landing gear until the tractor is lifted C) Leave the landing gear up D) Remove the landing gear

8. Glad hands are: A) Tools for fifth wheel inspection B) Air line couplers between tractor and trailer C) Hand brakes D) Mud flaps

9. The emergency air line is usually: A) Blue B) Red C) Green D) Yellow

10. If you connect glad hands incorrectly (cross them): A) Nothing will happen B) The brakes will not work properly C) The horn will sound D) The lights will dim

Fifth Wheel & Kingpin (Q11-Q15)

11. After coupling, you should visually check the fifth wheel jaws by: A) Looking from the driver's seat B) Getting out and looking with a flashlight to confirm the jaws are closed around the kingpin C) Tapping the trailer D) Reading the gauge

12. The fifth wheel locking lever should be: A) Up after coupling B) In the locked position with no gap visible C) Loose D) Removed during travel

13. If you see daylight between the trailer and fifth wheel after coupling: A) That's normal B) The connection is bad - do not drive C) Add more grease D) Drive slowly to seat it

14. The kingpin should be: A) Centered in the fifth wheel jaws B) Off to one side C) Above the fifth wheel D) Behind the fifth wheel

15. A sliding fifth wheel allows you to: A) Change tractor color B) Adjust weight distribution between axles C) Increase fuel mileage automatically D) Skip the inspection

Trailer Brakes & Air Systems (Q16-Q20)

16. Trailer air tanks should be drained: A) Never B) Daily, to remove water and oil C) Once a year D) Only when raining

17. The trailer hand valve (trolley valve) should be used: A) For parking B) To test the trailer brakes only, not for stopping the rig C) For every stop D) As the main brake

18. If the trailer breaks away from the tractor, the emergency brakes on the trailer should: A) Stay released B) Apply automatically C) Be applied by the driver D) Need a separate switch

19. When parked, you should: A) Use only the tractor parking brake B) Use both the tractor and trailer parking brakes C) Use only the trailer brake D) Leave brakes off if on level ground

20. Brake lag on a combination vehicle is approximately: A) Instant B) About half a second longer than a straight truck C) Five seconds D) Ten seconds

Off-Tracking & Driving (Q21-Q25)

21. Off-tracking means: A) The trailer follows the same path as the tractor B) The trailer wheels follow a tighter path than the tractor wheels in a turn C) The trailer flips over D) The tires lose grip

22. To compensate for off-tracking on a right turn: A) Stay close to the curb B) Swing wider, keeping the trailer wheels from cutting the curb C) Make the turn faster D) Use the trolley valve

23. The longer the trailer: A) The less off-tracking B) The more off-tracking C) Off-tracking stays the same D) Trailers don't off-track

24. When backing a combination vehicle, turning the steering wheel right will cause the trailer to: A) Move right B) Move left C) Stay still D) Jackknife immediately

25. To straighten out a trailer while backing, you should: A) Turn the wheel in the same direction as the trailer drift B) Pull forward and try again C) Speed up D) Use the trolley valve

Inspection & Safety (Q26-Q30)

26. Safety chains on a trailer are used to: A) Lock the doors B) Hold the trailer to the tractor if the fifth wheel fails (mostly on lighter trailers) C) Tie down cargo D) Adjust ride height

27. The landing gear should be: A) Fully raised before driving B) Halfway raised C) Down while driving D) Removed before driving

28. When inspecting a combination vehicle, you should check: A) Only the tractor B) Only the trailer C) Both the tractor and trailer, including all coupling points D) Just the tires

29. A jackknife is most likely when: A) Going uphill B) The drive wheels lock up on a slippery road C) Driving in a straight line D) Backing slowly

30. The most common cause of fifth wheel failure is: A) Improper coupling and inspection B) Bad weather C) Heavy loads alone D) High mileage alone

Real talk: Question 24 trips up more people than any other on this section. When you back, the trailer goes the opposite direction from where you turn the wheel. You turn right, trailer goes left. It's backwards from a car. The DMV examiner watches your alley dock and offset back like a hawk for this exact reason. Practice in a parking lot with cones before you go to a real yard.

Answer Key with DL 650 Citations

How to study so the test actually sticks

Reading questions once and clicking through the answer key isn't going to do it. The folks who pass first try work through the questions, write down the ones they got wrong, then go read that exact section in the DL 650. The handbook is free at any DMV office or online. Use it.

If you want every section covered the same way (general knowledge, air brakes, hazmat, doubles/triples), our California CDL air brakes practice test is the natural next step. Most people who pass the combination test also need air brakes since almost every Class A tractor runs them.

For folks who want everything in one place without bouncing between handbook PDFs and free quizzes, we put together a full prep package that covers all eight CDL test sections with worked answers and DL 650 page references. You can grab it here: CDL Pass Pack on Gumroad. It's the same questions style as above, just 10x more of them.

What to expect on test day

You'll sit at a DMV touchscreen, work through 20 questions, and get your result instantly. Miss more than 4 and you'll need to come back. Most California DMVs let you retake it the same day if there's time on the schedule, but don't bank on it - go in ready.

Bring your application paperwork, your medical card, your proof of residency, and your fee. Doors lock at closing, so get there early. If you're still figuring out the application side, our California CDL requirements 2026 guide walks through every document.

Pass on the first try

The combination test isn't hard if you actually work the material. Twenty questions, 80% to pass, and every answer is sitting in Section 6 of the DL 650. Run these 30 practice questions until you can answer them without looking, then run them again the night before. That's it. That's the whole strategy.

Good luck out there. The road's waiting.

Last updated: 2026-05-17