CDL · 10% of test plan

Combination Vehicles for the CDL Exam

Anyone with a Class A CDL must pass the Combination Vehicles knowledge test. The test is heavy on coupling/uncoupling sequence — the leading cause of dropped trailers.

Locale-specific study guides

Pass-rate data, regulatory context, and study tips for Combination Vehicles all change by candidate locale. Pick your context:

Common failure modes

These are the patterns that cause most candidates to lose marks on this topic. Recognising them in advance is half the work.

!Not chocking the trailer wheels before uncoupling
!Failing to pull-test the connection (low gear, gentle pull) after coupling
!Wrong air-line color: blue = service, red = emergency
!Forgetting to lower the landing gear before disconnecting

Study tips

1Drill the coupling sequence start-to-finish — examiners score sequence and verbal commentary.
2Memorize: blue line = service brakes, red line = emergency brakes & supply.
3Practice the visible-fifth-wheel-jaw rule: jaws must be closed around the kingpin shank, not just touching.
4Know the "tug test": low gear, gentle forward pull against locked trailer brakes.

Sample CDL Combination Vehicles questions

These sample items mirror the format and difficulty of real CDL questions. Practice with thousands more on the free Koydo question bank.

1
After coupling, you should test the connection by:
- APulling forward in low gear with trailer brakes lockedCorrect
- BReversing into the trailer at speed
- CSetting the parking brake and walking around the rig
- DConnecting the air lines and watching for pressure
Why this answer?
The tug test (low gear, gentle pull against locked trailer brakes) confirms the fifth-wheel jaws are fully locked around the kingpin. A connection that fails the tug test will drop the trailer.

Practice CDL questions free with Koydo.

Air-brakes, hazmat, pre-trip — every endorsement, every state. Built with a Pass Guarantee.

Start free CDL practice →See CDL pass rates by state