What 393.55D1-B means in plain language
This citation covers situations where the coupling devices or towing methods on your commercial motor vehicle are found to be defective or inadequate during a roadside inspection. In practical terms, that means an inspector looked at how your trailer connects to your tractor — the fifth wheel, kingpin, safety chains, pintle hooks, or any other hardware that keeps your combination vehicle together — and found something that didn't meet the standard.
"Defective or inadequate" is deliberately broad. It can apply to worn fifth-wheel locking jaws that don't fully engage, a cracked or bent kingpin, missing or improperly secured safety chains, or towing hardware that simply isn't rated for the load being pulled. The regulation applies to the full range of coupling and towing equipment on any commercial motor vehicle.
The bottom line for a driver who just got cited: the inspector's finding is logged against your operating authority and feeds into your CSA score. With a severity weight of 8 out of a possible 10, this is not a low-impact citation — it carries more weight than many other vehicle maintenance violations.
What our enforcement data actually shows
Across our database of 13 million+ roadside inspection records, 393.55D1-B has generated 22,987 all-time citations. In the last 12 months alone, our inspection records show 12,087 citations for this code — meaning more than half of all historical citations have occurred in just the past year, a clear indicator of rising enforcement attention. In the last 90 days, 2,460 citations were recorded.
Despite that volume, the out-of-service rate for this code is 0.0% across all 22,987 citations in our database. Not a single driver was placed out of service on this code. That is a striking contrast to the all-FMCSR average OOS rate of 31.4%. In other words, inspectors are consistently finding and documenting defective coupling conditions without pulling drivers off the road — which tells you this code is being written primarily as a corrective-record violation, not an immediate safety stop. Still, a severity weight of 8 means the CSA points accumulate quickly, and the citation is real regardless of whether you drove away.
This code ranks #123 out of 3,036 FMCSR codes by citation volume nationally — placing it firmly in the top 5% of all codes by enforcement frequency.
Looking at the monthly trend over the last 12 months, citations have been consistently high: our data shows months ranging from 940 to 1,142 citations, with March 2026 coming in at 1,114. Enforcement volume has not softened — if anything, it has stabilized at an elevated level compared to earlier periods.
Who gets cited most
Among states, the highest citation counts in the last 180 days come from New York (447 citations), California (373 citations), and Arizona (193 citations). All three states share the same 0.0% OOS rate for this code, so there is no meaningful difference in how aggressively inspectors across those states pull drivers off the road — the citation gets written, but the truck keeps moving.
The state-level distribution tells a broader story: New York and California are consistently high-enforcement environments for vehicle maintenance codes in general, and their citation counts here reflect both inspection volume and inspector familiarity with coupling equipment deficiencies.
On the carrier side, our data shows fleets such as VRP TRANSPORTES DE MEXICO S DE RL DE CV (USDOT 662058) with 140 all-time citations, and SERGIO VARELA MALDONADO (USDOT 725226) with 103 citations. The concentration of citations among cross-border carriers in the top-cited list is notable — coupling hardware that meets standards on one side of the border can present inspection findings on the other side, making pre-crossing inspections especially important for international operations.
How severe is this compared to similar codes
To put 393.55D1-B in context, consider a few peer codes in the Vehicle Maintenance category tracked in our database.
396.3(a)(1) — Inspection/repair/maintenance (general) has accumulated 236,919 citations with a 45.3% OOS rate. That code puts nearly half its cited drivers out of service. By comparison, 393.55D1-B's 0.0% OOS rate means the consequences fall entirely on your CSA score rather than your ability to move the load.
393.47E — Slack adjuster defective has 180,363 citations and a 0.0% OOS rate — a profile very similar to 393.55D1-B in terms of how inspectors handle it at the roadside. Both codes result in citations without OOS placement, but both carry meaningful CSA severity.
393.9(a) — Inoperable required lamps sits at 660,737 citations with a 15.4% OOS rate. That code is written far more often and puts a meaningful share of drivers out of service — a different risk profile entirely.
The takeaway: 393.55D1-B won't stop your truck, but at a CSA severity weight of 8 and a top-125 national citation rank, it accumulates risk on your safety measurement score in a way that affects carrier interventions and insurance exposure over time.
How to avoid it
Our data on the 2,460 citations in the last 90 days shows that 393.55D1-B almost never travels alone. The most commonly co-occurring codes give you a direct roadmap of what inspectors are finding at the same time. Build these checks into every pre-trip:
- Inspect the fifth wheel completely. Walk around and verify the locking jaws have fully engaged around the kingpin. Tug the trailer forward with the tractor in low gear before releasing the parking brake to confirm the connection is solid. A loose or partially latched fifth wheel is the fastest path to this citation.
- Check coupling hardware for wear and damage. Look for cracks in the fifth-wheel plate, bent or worn kingpins, and damaged safety chains or cables. The citation is specifically about defective or inadequate hardware — visual wear counts.
- Inspect brake and steering components at the same time. Our inspection records show 393.47E (slack adjuster defective) appearing in 308 of the same inspections as 393.55D1-B in the last 90 days, and 393.53B-B (steering system components worn) appearing in 297. If an inspector is already under your truck for a coupling issue, they are checking slack adjusters and steering components. Don't give them more to write.
- Check fuel system integrity. 396.5B-L (fuel system leak) co-occurred in 457 shared inspections in the last 90 days. A pre-trip walk-around that catches a dripping fuel line also signals to an inspector that the vehicle is maintained — or not.
- Verify lights and glazing. 393.78A-WS (windshield condition defective) appeared in 358 of the same inspections, and 393.9A-LIL (inoperable required lamps) in 243. Burned lamps and cracked windshields are inspector triggers that lead to a full inspection — which is when coupling hardware gets examined.
- Pay extra attention if you operate a Freightliner or International. Our data shows Freightliner units account for 6,057 all-time citations under this code, and International units for 2,823. Those are the two most-cited makes by a significant margin. If you're running either platform, make fifth-wheel and towing hardware inspection a non-negotiable pre-trip step.