How do you check the locking jaws?

Look into the gap at the back of the fifth wheel and say the jaws are closed around the kingpin with no play, the release arm is engaged and the safety latch is in place.

Is the coupling inspection on the Class B test?

No. It is part of the Class A test, because only combination vehicles have a fifth wheel and kingpin.

CDL coupling inspection: fifth wheel, kingpin and locking jaws

Updated October 2026 · Written from the state CDL manuals

The coupling inspection is the Class A part of the CDL pre-trip: you check everything that holds the trailer to the tractor. There are four items: the air and electric lines, the fifth wheel skid plate, the kingpin and apron, and the locking devices. The one that matters most is the locking jaws: look into the gap and say they are closed around the kingpin.

Only for combination vehicles (Class A).
Look into the gap behind the fifth wheel: jaws closed around the kingpin, no play.
The trailer must sit flat on the fifth wheel, with no gap between the apron and the plate.

What the examiner wants to hear

Pointing at the fifth wheel is not enough. For each part, name it and say what could be wrong: lines not cut, chafed or dragging; plate securely mounted and greased; kingpin not bent; jaws closed; release arm engaged; safety latch in place. Being specific is how you show the trailer cannot come loose.

The locking jaws: what to look for and say

What to say

“I look into the gap at the locking jaws.”
“They're closed around the kingpin, with no play.”
“The release arm is engaged.”
“The safety latch is in place.”
“The slider locking pins are fully engaged.”

What the examiner listens for

Jaws closed on the kingpin
Release arm engaged
Safety latch in place

Every coupling item on the checklist

4 items. What to point at and what the examiner expects you to say about each.

Item	What to check
Air & electric lines & connectors	Names air and electric lines · Connectors seated and locked · Not cut, chafed, spliced or taped · Not tangled, pinched or dragging · No air leaks Script in the app
Fifth wheel skid plate	Names the fifth wheel skid plate · Securely mounted · No loose or missing parts · No cracks, breaks or heavy wear Script in the app
Kingpin & apron & gap	Names the kingpin and apron · Kingpin not bent, damaged or worn · Apron not bent, cracked or broken · No gap Script in the app
Locking & safety devices	Jaws closed on the kingpin · Release arm engaged · Safety latch in place Script and video

After coupling comes the trailer itself: landing gear raised with the crank handle secured, and reflective tape present. Both are in the full checklist.

The script for every item, not just this one

Mr. Egg's 32 short video lessons cover the whole walk-around with the exact words for each item. Record yourself saying it back, then run a timed mock inspection scored by an AI examiner.

Get all the scripts in the app

See the whole walk-around: all 32 items on the CDL pre-trip checklist.

Questions people ask

That the skid plate is securely mounted, has no loose or missing bolts, nuts, pins or brackets, no cracks or heavy wear, and is greased; that the kingpin is not bent or worn and the apron is not cracked; that there is no gap between the trailer and the fifth wheel; and that the locking jaws are closed around the kingpin.