What 393.71(j) means in plain language
A citation for 393.71(j) means an inspector found that your fifth wheel assembly—the coupling device that connects your tractor to a semi-trailer—is defective, showing excessive wear, or not properly secured to the vehicle frame.
The fifth wheel is one of the most critical load-bearing components on your rig. It transfers all the weight and braking force from the trailer to the tractor, and it bears the full dynamic load during turning, stopping, and acceleration. If it's worn, cracked, has loose bolts, or shows play between the upper and lower fifth wheel, you've got a safety failure that can lead to jackknife, trailer drift, or catastrophic uncoupling at highway speed.
An inspector looking at your fifth wheel is checking for visible cracks, corrosion, bent or missing fasteners, worn kingpin pockets, loose mounting bolts to the frame, or horizontal or vertical play when they grab the trailer and try to move it. Any of these conditions triggers the violation—you don't have to wait for a failure to occur.
What our enforcement data actually shows
Across our 13 million inspection records, 393.71(j) citations are rare. We've recorded 13 all-time citations for this code, with zero citations in the last 12 months and zero in the last 90 days. This places it at rank #2110 out of 3,036 FMCSR codes by citation volume.
However, when inspectors do cite this code, the consequences are severe. Our data shows that 12 out of 13 citations—a 92.3% out-of-service rate—resulted in the vehicle being placed out of service on the spot. This is nearly three times higher than the all-FMCSR average of 31.4%. That means if you get cited for 393.71(j), there's a very high likelihood you're not moving that rig until the defect is repaired and a follow-up inspection confirms it.
Note that 393.71(j) is not itself an out-of-service-eligible violation, meaning an inspector has discretion. But the rarity of citations combined with the high OOS rate suggests inspectors rarely write this code unless the defect is serious enough to warrant immediate repair.
Who gets cited most
Our enforcement database does not provide a state-level breakdown for this specific code due to its low citation volume. However, our data shows that fleets such as N AND N TRANSPORT EXPRESS INC (USDOT 2636801) and GRUPO LOZANO TANSPORTES LLC (USDOT 3495206) each received 2 citations for fifth wheel defects in our all-time records. All other carriers in our top-violators list for this code had 1 citation each. This distribution reflects the rarity of the violation across the industry—even the most-cited carriers for this specific defect have very few incidents.
How severe is this compared to similar codes
393.71(j) belongs to the Vehicle Maintenance category, where it sits alongside codes like:
- 393.9(a) — Inoperable required lamps: 660,737 citations, 15.4% OOS rate. This code is cited far more frequently, but inspectors place vehicles out of service much less often.
- 396.3(a)(1) — Inspection/repair/maintenance (general): 236,919 citations, 45.3% OOS rate. Also more common, but with a lower OOS rate than 393.71(j).
- 393.47E — Slack adjuster defective: 180,363 citations, 0.0% OOS rate. Slack adjusters are brake-related and cited much more often, yet rarely result in OOS placement.
The 92.3% OOS rate for 393.71(j) underscores that fifth wheel defects are treated as high-priority safety issues. When cited, they almost always ground the vehicle immediately.
How to avoid it
Fifth wheel maintenance is a critical pre-trip task. Here's what you need to check:
- Walk the undercarriage before every load. Get under the trailer while it's still hitched and visually inspect the fifth wheel upper assembly for cracks, corrosion, or visible separation from the frame. Look for rust bloom or weeping that signals internal stress.
- Check kingpin pockets for wear. Grab the trailer leg firmly and try to move it side to side and front to back by hand. Any play or clunking means the pocket is worn and the fifth wheel needs service.
- Verify all mounting bolts are tight. A wrench-check of the four corner bolts connecting the upper fifth wheel to the tractor frame takes 90 seconds and can catch a loose fastener before an inspector does.
- Inspect for bent or missing fasteners on the lower fifth wheel assembly beneath the trailer. Missing or bent bolts degrade the connection and may indicate prior impact or wear.
- Grease regularly on schedule. A properly lubricated fifth wheel reduces wear and helps you spot leakage or contamination during maintenance that signals internal damage.
- Know your truck's age and service history. If your fifth wheel has never been rebuilt or replaced and your tractor exceeds 500,000 miles, budget for a professional inspection or rebuild. Fifth wheels wear over time, and proactive replacement is cheaper than a roadside violation.
- Never overlook trailer coupling issues. If you feel drag, play, or noise during coupling, do not assume it's the trailer's landing gear. Inspect your fifth wheel—the upper assembly wears at the same rate as the kingpin.