What 393.55D2-B means in plain language
FMCSR 393.55D2-B targets the hardware that physically connects your trailer to your tractor — the fifth wheel, kingpin, drawbars, pintle hooks, safety chains, and any other component involved in the coupling or towing arrangement. The violation is written when an inspector determines that one or more of those components is defective or not adequate for the load or configuration being pulled.
This isn't about a loose strap or a minor cosmetic issue. Inspectors are looking for worn or cracked fifth-wheel plates, kingpins with excessive play, missing or damaged locking mechanisms, and towing hardware that isn't properly rated or secured for the trailer attached. If any part of the connection between your power unit and your trailer fails the inspector's eye, 393.55D2-B is the code that lands on your inspection report.
Note that this specific sub-code sits within the broader 393.55 family. You may see related codes like 393.55D1-B or 393.55E-B on the same inspection — those cover overlapping aspects of the same coupling system, and our data shows they frequently appear together.
What our enforcement data actually shows
Across our database of 13 million+ inspections, 393.55D2-B has generated 15,737 all-time citations. What's immediately notable is the out-of-service rate: 0.0%. Not a single one of those 15,737 citations resulted in a driver being placed out of service. By comparison, the all-FMCSR average OOS rate across all codes is 31.4%, which means this code sits dramatically below the national baseline. You will keep rolling — but the citation still follows you.
The enforcement volume is accelerating. Our inspection records show 8,724 citations in the last 12 months alone, and 1,579 citations in just the last 90 days. That's a significant share of the all-time total compressed into a very short window, which tells fleet managers that inspectors are actively writing this code with increasing frequency. Among all 3,036 FMCSR codes tracked in our database, 393.55D2-B ranks #167 by citation volume — meaning it sits well inside the top 6% of most-cited codes nationwide.
Looking at the monthly trend, the data in our database indicates volume spiked to 981 citations in a single month (May 2025) before settling into a sustained range of 625–889 citations per month through early 2026. There is no month in the last year where citations dropped to zero or even close — this code is being enforced consistently across all seasons.
The CSA severity weight is 8 out of a possible 10. Even though you aren't going out of service at the roadside, an 8-weight violation moves your Vehicle Maintenance BASIC score meaningfully. If you accumulate multiple citations in a 24-month window, the scoring algorithm compounds the impact.
Who gets cited most
Looking at the last 180 days, California leads all states with 404 citations, followed closely by New York at 306 citations and Arizona at 289 citations. All three states recorded a 0.0% OOS rate, consistent with the national picture for this code. The OOS rates across the top states show no material variation — no state is writing this code and then pulling drivers off the road.
The geographic concentration around border-adjacent states and major freight corridors is telling. Our inspection records show that among carriers with the highest all-time citation counts, fleets such as AUTOTRANSPORTES ROMEDU SA DE CV (USDOT 1148259) with 124 citations and TRANSPORTES DE CARGA FEMA SA DE CV (USDOT 1175018) with 93 citations appear at the top of the list. The pattern of carrier names in our data broadly reflects the heavy cross-border freight activity that moves through California, Arizona, and Texas — routes where coupling hardware endures high-mileage stress cycles and frequent trailer swaps.
On the equipment side, Freightliner units account for 4,566 all-time citations under this code — by far the most of any make. International trucks follow at 1,826 citations, and Volvo at 1,678 citations. These are the three most common power units in long-haul freight, so the counts partly reflect fleet population size, but they also tell you that no major make is exempt from this inspection finding.
How severe is this compared to similar codes
Within the Vehicle Maintenance category, 393.55D2-B is a mid-volume code with a uniquely low OOS rate. Consider the contrast with a few peers. The general maintenance code 396.3(a)(1) — Inspection/repair/maintenance - general — has accumulated 236,919 citations in our database with a 45.3% OOS rate. That means nearly half of those inspections ended with a driver parked. Under 393.55D2-B, zero drivers were parked.
Slack adjuster code 393.47E — Slack adjuster defective — shows 180,363 citations and a 0.0% OOS rate, making it a closer structural parallel to 393.55D2-B: high volume, no OOS, but still a severity-weighted citation that damages your BASIC. The inoperable lamps code 393.9(a) carries 660,737 citations and a 15.4% OOS rate — a reminder that not all maintenance codes are written with the same restraint inspectors show on coupling devices.
The takeaway for fleet managers: 393.55D2-B won't strand your driver, but its CSA weight of 8 makes it one of the more expensive non-OOS citations in the Vehicle Maintenance BASIC.
How to avoid it
The co-occurring violation pattern in our inspection records is a direct roadmap for your pre-trip checklist. In the last 90 days, 393.55D2-B appeared on the same inspection as 393.55E-B (another coupling device defect code) 606 times, and alongside 393.47E (slack adjuster defective) 215 times. Brake tubing codes 393.45D-B and 393.45B2-B-AIR appeared together with this code 178 and 173 times respectively. That pattern tells you inspectors who find one problem in the coupling and brake hardware area keep looking — and keep finding.
- Fifth wheel inspection — every pre-trip: Grab the trailer kingpin and check for excessive lateral play before you hook up. Visually confirm the locking jaw is fully engaged and the release handle is properly seated. On Freightliner, International, and Volvo tractors — the three most-cited makes in our data — check the fifth wheel mounting bolts for looseness while you're down there.
- Kingpin wear check: Use a kingpin wear gauge if your fleet provides one. Inspectors use them at roadside. A worn kingpin that passes a visual check may still fail a gauge measurement.
- Slack adjusters during the same walk-around: Since 393.47E co-occurs 215 times with this code, manually check each slack adjuster for proper stroke while you're already under the trailer. A single walk-around catches both.
- Brake tubing visual sweep: With 393.45D-B and 393.45B2-B-AIR each appearing on nearly 175 shared inspections, scan air lines and brake hoses for chafing, kinking, or leaks while checking the coupling hardware.
- Safety chains and secondary connections: Confirm safety chains or cables are properly attached, not twisted around each other, and rated for the trailer being towed. Missing or damaged secondary connections are a common trigger for the 393.55 family of codes.
- Document your pre-trip: A signed DVIR showing you inspected the coupling system is your first line of defense if an inspector finds a borderline condition and questions whether you were paying attention.