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A
There is no such thing as a high hookup
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B
A high hookup occurs when the trailer nose is too high for the fifth wheel — the kingpin rides on top of the fifth wheel plate rather than in the jaws; the connection appears made but is not properly secured and can release under load
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C
A high hookup puts extra weight on the steer axle only
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D
High hookup means the trailer is too far forward on the tractor
Why this is the answer
HIGH HOOKUP is a dangerous coupling error where the trailer is positioned too high relative to the fifth wheel when coupling is attempted. WHAT HAPPENS: The kingpin contacts the FRONT EDGE of the fifth wheel's jaws but does not descend into the jaws properly; the jaws may partially close around the kingpin's upper shaft rather than at the correct locking groove; the trailer appears to be coupled and may even pass an initial tug test at very low force, but is NOT secure for highway operation. CAUSES: Landing gear set too high before backing the tractor under; trailer nose elevated due to uneven parking surface; fifth wheel height not properly matching the trailer height. DETECTION: After coupling, verify the trailer sits flat on the fifth wheel plate — no gap between the fifth wheel and the bottom of the trailer; if a gap exists, the hookup is incorrect; walk around and view from the side; check for the tilt of the trailer relative to the tractor. CONSEQUENCES: At highway speeds and during braking, the force on the coupling can exceed the partial engagement's strength, causing complete separation — a runaway trailer is an immediate, potentially fatal hazard for all traffic behind it. PRE-TRIP PREVENTION: Always check trailer height before backing under; use the correct fifth wheel height for your trailer type; complete the tug test; visually verify the trailer is seated fully on the fifth wheel plate.
Source: FMCSA CDL Manual, Chapter 6, Combination Vehicles, Coupling Errors