247SimpleTests
CDL · Coupling and Uncoupling

After coupling, how should a driver verify the fifth wheel is properly locked onto the kingpin?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

Visually inspect from underneath/the side with a flashlight to confirm the locking jaws have closed around the kingpin shank (not the head), there is no gap between the trailer and fifth wheel, and the locking lever/handle is in the locked position — plus perform a tug test

  1. A Visually inspect from underneath/the side with a flashlight to confirm the locking jaws have closed around the kingpin shank (not the head), there is no gap between the trailer and fifth wheel, and the locking lever/handle is in the locked position — plus perform a tug test
  2. B Drive forward at high speed to test
  3. C Honk the horn twice
  4. D Just look at it from the driver's seat

Why this is the answer

Verifying the coupling: After backing under, verify the connection by: (1) TUG TEST: With the trailer brakes locked, gently pull forward against the kingpin — the tractor and trailer should not separate; (2) VISUAL INSPECTION: Get out and look under the trailer with a flashlight; confirm the LOCKING JAWS have closed completely around the kingpin SHANK (the narrow part), NOT just resting on the kingpin head; confirm there is NO GAP between the trailer apron and the fifth wheel (a gap indicates a high hitch); confirm the locking lever/handle is in the LOCKED position and the safety latch (if equipped) is engaged; THE DANGER — HIGH HITCH: When the fifth wheel jaws close in front of or on top of the kingpin head rather than around the shank — it may hold briefly then release, dropping the trailer; ALWAYS do both the tug test AND a visual inspection — never rely on sound or feel alone; this verification is critical to prevent trailer separation.

Source: FMCSA CDL Manual — Coupling Verification

Practice more questions

This question is from our CDL Practice Tests practice test. Take the full practice test to test your knowledge across all Coupling and Uncoupling and other topics.

Take the Combination Vehicles practice test →

About this topic: Coupling and Uncoupling

A bad coupling can drop the trailer or separate it from the tractor at speed. The tug test, visual inspection of the kingpin, and proper line-up are the defenses. This is one of 19 Combination Vehicles questions on coupling and uncoupling, each with a full explanation on a single study page.

New to this exam? Our CDL exam guide explains the format, scoring, and how to prepare.

Related questions

Coupling and Uncoupling

What is the proper order for the steps of coupling a tractor to a trailer?

 Coupling and Uncoupling

After coupling, how do you verify the trailer is securely connected to the tractor?

 Coupling and Uncoupling

Before uncoupling a trailer, what must you do first?

 Coupling and Uncoupling

What is a 'glad hand' on a combination vehicle?

State-specific guides

Need information for your state? Our state guides cover local requirements, fees, and what to expect on exam day.

California Texas Florida New York Pennsylvania Illinois Ohio Georgia

Recommended study materials

Study guide

CDL Study Guide (Trivium)

Complete prep for all CDL written tests: general knowledge, air brakes, combination vehicles, hazmat, and all endorsements. Includes full-length practice tests.

Check Price → Study guide

CDL Practice Tests & Flashcards (Accepted Inc.)

600+ practice questions covering every FMCSA knowledge area, plus 400 flashcards for endorsement prep.

Check Price → Study guide

Master the CDL Truck Driver's License (Arco)

Arco's classic CDL prep with in-depth FMCSA manual coverage, endorsement chapters, and scored practice exams.

Check Price →

As an Amazon Associate, CJ Affiliate, and AWIN publisher we earn from qualifying purchases. Links above are affiliate links. Full disclosure →