What 393.71(k) means in plain language
Code 393.71(k) addresses the fifth wheel assembly on your truck—the heavy-duty coupling mechanism that connects your tractor to a semi-trailer. When an inspector cites this code, they're flagging one or more issues: the fifth wheel is broken or damaged, shows signs of excessive wear that compromises its function, or isn't properly bolted and secured to the frame.
This isn't about cosmetic damage. The fifth wheel bears the full weight and dynamic forces of your loaded trailer during acceleration, braking, and cornering. If it fails—or if it's loose—you lose the ability to control the trailer safely. An unsecured or defective fifth wheel can cause a jackknife, trailer sway, or catastrophic separation on the highway.
Inspectors look for cracks in the casting, worn locking jaws that don't grip the kingpin securely, rust or corrosion that weakens structural integrity, missing or damaged fasteners, and play or movement in the assembly when they rock the trailer side to side. If they find any of these, you'll be cited under 393.71(k).
What our enforcement data actually shows
Across our 13 million+ inspection records, 393.71(k) citations are uncommon. We've recorded 54 all-time citations for this code, with zero citations in the last 12 months and zero in the last 90 days. This ranks 393.71(k) at #1607 out of 3,036 FMCSR codes by citation volume.
When this code is cited, however, enforcement is serious: 10 of those 54 citations—an 18.5% out-of-service rate—resulted in the truck being pulled from service immediately. This is significantly lower than the all-FMCSR average OOS rate of 31.4%, suggesting that when inspectors find a fifth wheel problem, they often issue a warning or allow the driver to correct it quickly rather than immediately grounding the vehicle. That said, one in five citations does lead to an OOS order, so the defect is treated with weight.
Who gets cited most
Our data shows that this violation is concentrated among a small number of carriers and vehicle types. The top carriers cited for 393.71(k) include DUSTIN C NOLAN LOGGING LLC with 2 citations and TIMBER RIDGE RESOURCES LLC with 2 citations. The rarity of this citation across the database means no single geographic pattern dominates; enforcement is sporadic and tied to individual inspections rather than systemic fleet issues.
By vehicle make, Freightliner trucks accounted for 8 of the 54 citations, followed by Kenworth and Peterbilt with 4 each. If you operate a Freightliner, Kenworth, or Peterbilt, pay close attention to fifth wheel condition during your pre-trip.
How severe is this compared to similar codes
Code 393.71(k) sits in the Vehicle Maintenance category alongside codes like 393.9(a) (Inoperable required lamps), 396.3(a)(1) (Inspection/repair/maintenance general), and 393.47 (Slack adjuster defective). The contrast is striking: 393.9(a) has been cited 660,737 times with a 15.4% OOS rate, while 396.3(a)(1) has 236,919 citations with a 45.3% OOS rate. Code 393.71(k)'s 54 all-time citations make it rare by comparison, but its 18.5% OOS rate suggests inspectors treat fifth wheel defects seriously when they do find them.
This rarity doesn't mean it's unimportant—it likely means most drivers catch the problem themselves during pre-trip inspection or that fifth wheel maintenance is generally well-practiced across the industry. When it is cited, the elevated OOS rate shows it's not a trivial finding.
How to avoid it
Preventing a 393.71(k) citation requires a methodical pre-trip inspection focused on the fifth wheel assembly:
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Check fifth wheel fasteners every morning. Walk around the tractor frame where the fifth wheel bolts attach. Look for missing bolts, loose fasteners, or bolts that have backed out. Bring a wrench and check each bolt for tightness. A loose bolt can work its way out over the course of a trip.
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Inspect the locking jaws and kingpin fit. Couple and uncouple your trailer in the yard. The kingpin should slide smoothly into the jaws, and when locked, there should be no visible play or wobble. If the jaws feel springy or loose, or if you see daylight between the kingpin and the jaws after locking, get it serviced before you roll.
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Look for cracks and corrosion. Examine the fifth wheel casting—the heavy metal component itself—for visible cracks, deep rust, or pitting that has eaten into the metal. Paint over surface rust is normal; structural corrosion is not. If you see through rust or active flaking, report it.
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Check for wear on the top plate. The underside of your trailer's kingpin rests on the fifth wheel's top plate. Over time, this surface wears smooth. If the top plate is polished shiny but the locking action still feels secure, you're fine. If the locking mechanism feels weak or loose despite apparent smoothness, get it replaced.
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Verify the coupling is fully engaged. After coupling, ensure the locking handle is in the fully locked position and cannot move freely. A locked fifth wheel should not rock or shift when you bounce the trailer vertically or pull it side to side by hand.
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Schedule maintenance if you notice any degradation. Don't wait for an inspection to find a problem. If your fifth wheel is over five years old or has high mileage, ask your shop to inspect and lubricate it during regular service. Preventive maintenance on the fifth wheel is far cheaper than an OOS citation and the downtime that follows.
The good news: this code is rare because most operators get this right. Stay disciplined with your pre-trip routine, and you'll avoid it.