What 393.71(b) means in plain language
FMCSR 393.71(b) requires that the fifth wheel assembly on your commercial motor vehicle be in proper working condition, free from excessive wear, and correctly secured to the frame. The fifth wheel is the coupling mechanism that connects your tractor to a semi-trailer, and it bears the entire weight and motion load of the trailer behind you.
When an inspector cites you for 393.71(b), they're saying one of three things happened: the fifth wheel itself is damaged or defective, it shows signs of wear that compromise its function, or it isn't bolted down and secured the way the manufacturer and FMCSA require. A loose, worn, or broken fifth wheel creates an immediate safety hazard—your trailer could shift, jackknife, or separate from the tractor entirely.
This isn't a minor cosmetic issue. Fifth wheel failure can cause catastrophic accidents. That's why inspectors treat defects in this component seriously, and why you should too.
What our enforcement data actually shows
Our inspection records show that 393.71(b) violations are uncommon in the roadside inspection universe. Across our 13 million+ inspection records, there has been 1 all-time citation for fifth wheel defects. In the last 12 months, we recorded 0 citations, and in the last 90 days, 0 citations. This code ranks #2,796 out of 3,036 FMCSR codes by citation volume—placing it in the bottom tier of enforcement activity.
When violations do occur, they rarely result in an out-of-service order. Our data shows an OOS rate of 0.0% for this code (0 out of 1 citation resulted in an OOS placement). By comparison, the all-FMCSR average OOS rate is 31.4%, meaning fifth wheel defects, when cited, typically do not trigger immediate vehicle removal. This likely reflects the fact that inspectors may cite the defect as a repair-before-operation notice rather than a roadside safety-critical failure.
The rarity of citations doesn't mean you should ignore fifth wheel maintenance. Rather, it suggests that most fleets are maintaining fifth wheels adequately, and that when defects are found, they're often minor enough to correct without an immediate OOS.
Who gets cited most
Our database contains only 1 all-time citation for 393.71(b). That citation was issued to a vehicle with a FORD fifth wheel. The cited fleet was Epolitos Towing Recovery LLC (USDOT 2484411), which appears once in our records for this violation. With so little enforcement volume, we cannot reliably identify state or regional trends for this specific code.
How severe is this compared to similar codes
Vehicle maintenance codes in the same category as 393.71(b) show vastly different enforcement frequencies. For perspective:
393.9(a) — Inoperable required lamps has been cited 660,737 times with a 15.4% OOS rate. This is a high-volume, moderate-severity violation.
396.3(a)(1) — Inspection/repair/maintenance general has accumulated 236,919 citations with a 45.3% OOS rate—among the highest OOS rates in the vehicle maintenance category, reflecting the safety-critical nature of general maintenance defects.
393.47E — Slack adjuster defective (brake-related) shows 180,363 citations with a 0.0% OOS rate, similar to 393.71(b) in that it's cited but rarely results in immediate out-of-service placement.
The fifth wheel, like slack adjusters, is a structural component whose failure is rare when maintenance protocols are followed. The dramatic difference in citation volume between 393.71(b) and codes like 393.9(a) or 396.3(a)(1) suggests that fifth wheel defects are preventable through diligent inspection and that most carriers are doing this work.
How to avoid it
Before every trip:
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Walk around the fifth wheel assembly during your pre-trip inspection. Look for visible cracks, rust, bent metal, or daylight between the fifth wheel and the mounting plate. A properly installed fifth wheel sits flush against the frame.
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Check all bolts and fasteners that secure the fifth wheel to the tractor frame. Use a wrench or socket to verify they are snug—not over-tightened, but not loose either. A loose bolt is the fastest way to get cited and create a safety hazard.
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Look for signs of excessive wear on the kingpin hole and the locking mechanism. If the kingpin slides in and out too easily, or if you see metal shavings or deep gouging, the fifth wheel is worn beyond safe limits.
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Verify the locking jaws close completely around the kingpin when you hook up. Listen for the audible click. A worn fifth wheel may lock but not hold securely under load.
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Inspect the mounting plate and frame rails for cracks radiating from the bolt holes. Frame cracks indicate structural failure and require immediate repair, not roadside fixes.
Every few weeks or per your fleet maintenance schedule:
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Have a qualified mechanic perform a detailed fifth wheel inspection, including measurement of wear on the locking jaws and kingpin contact surfaces. Replace the assembly if wear exceeds manufacturer specs—don't try to extend its life.
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Check all mounting bolts with a torque wrench to ensure they meet OEM specifications. Retighten as needed.
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Document these inspections and keep records in your vehicle. Inspectors may ask to see proof of maintenance.
The data shows that fifth wheel defects are caught infrequently, which means compliance is high. Maintain that standard by making fifth wheel inspection part of your routine, not an afterthought.