What 393.55D2 means in plain language
FMCSR 393.55D2 targets the connection points between your power unit and whatever you're pulling. In plain terms, it requires that the hardware and methods used to hitch a trailer or towed vehicle to a commercial motor vehicle must be in sound working condition and fully up to the task.
An inspector who cites you under this code has determined that a coupling device — think fifth wheels, pintle hooks, drawbars, safety chains, or any related hardware — is in a condition that makes it defective or inadequate for the load or operation at hand. It's not just about visible damage; an improperly matched or installed coupling can trigger the same citation even if nothing looks broken to the untrained eye.
The code covers the full range of towing configurations seen in commercial trucking. Whether you're running a standard dry van, a lowboy, or a specialty tow setup, the requirement is the same: every component in the coupling system must be functional and appropriate for the application.
What our enforcement data actually shows
Here's the first thing you should know if you've just been cited: this violation almost never puts a truck on the side of the road. Across all 2,884 citations in our inspection records, only 4 trucks were placed out of service — an OOS rate of just 0.1%. For context, the all-FMCSR average OOS rate across every code in our database is 31.4%. That means 393.55D2 results in out-of-service orders at roughly one-third of one percent of the rate you'd expect from a typical FMCSR violation. You can most likely keep moving after this citation.
That doesn't mean you should ignore it. The CSA severity weight for 393.55D2 is 8 out of a possible 10, which is high. That weight hits your Carrier's Vehicle Maintenance BASIC score and lingers on your record. The violation doesn't park you today, but it can contribute to an investigation or intervention down the road.
In terms of raw enforcement activity, our database shows 1,856 citations issued in the last 12 months alone, and 385 in just the last 90 days. This is not an obscure, rarely-enforced code — it ranks #448 out of 3,036 FMCSR codes by all-time citation volume. Inspectors know to look for it. The monthly trend in our records shows consistent enforcement pressure, with citation counts ranging from 133 to 197 per month over the past year.
Who gets cited most
Looking at the last 180 days of data, Texas dominates enforcement of this code by a wide margin. Our inspection records show 712 citations issued in Texas during that window, with only 1 OOS event — a 0.1% rate. Illinois comes in second with 66 citations and a 0.0% OOS rate, followed closely by Iowa with 63 citations, also at 0.0%. New Mexico and North Carolina appear in the data as well, but at much lower volumes. If you operate in Texas corridors, this code is one you need to have on your radar.
Among the carriers appearing most frequently in our data, our records show fleets such as National Drayage Services DE LLC (USDOT 1747093) with 8 all-time citations and Servicio Internacional de Enlace Terrestre SA DE CV (USDOT 818175) with 7 citations. Citation frequency in our data reflects inspection exposure and operational patterns, not a judgment on any carrier's safety culture.
Looking at vehicle makes, Freightliner units (FRHT) account for 956 all-time citations — the highest of any make — followed by Kenworth (KW) at 523 and Peterbilt (PTRB) at 367. If you're behind the wheel of any of these trucks with a trailer in tow, coupling hardware inspection deserves extra attention at every pre-trip.
How severe is this compared to similar codes
Within the Vehicle Maintenance category, 393.55D2 sits in a different tier than some of the most-cited codes, but its severity weight still makes it consequential.
Consider 393.9(a), covering inoperable required lamps, which has 660,737 all-time citations in our database and a 15.4% OOS rate. That code is cited far more often, and a meaningful share of those inspections end with the truck parked. By comparison, 393.55D2's 0.1% OOS rate means you're almost never getting sidelined, but you're also getting a severity-8 hit that a lamp violation may not carry.
Look at 396.3(a)(1), the general inspection, repair, and maintenance code, which shows 236,919 citations and a 45.3% OOS rate in our records. That's a code that regularly ends a driver's day. Again, 393.55D2 is far less likely to result in an OOS order, but its high severity weight means the CSA damage is disproportionate to the immediate enforcement outcome.
Finally, 393.47E — slack adjuster defective — has 180,363 citations in our database with a 0.0% OOS rate, similar to 393.55D2 on the OOS side, but with dramatically higher citation volume. Knowing that both codes share a near-zero OOS rate helps frame 393.55D2: it's a citation that hurts your CSA score more than it grounds your truck.
How to avoid it
The co-occurring violation pattern in our 90-day data tells a clear story about what inspectors are finding alongside 393.55D2. Use that pattern to build a tighter pre-trip.
- Check your fifth wheel or pintle hook latch completely. This is the core of the citation. Manually test the latch mechanism — it should not release under upward pressure from the trailer. Inspect the jaw, locking pin, and apron contact surface for wear, cracks, or deformation.
- Walk the full length of your safety chains or cables. With 393.55E (a closely related coupling code) appearing in 100 shared inspections in our 90-day data, inspectors are clearly looking at the entire coupling system — not just the primary hitch. Chains should have appropriate slack, proper hooks, and no kinks or broken links.
- Inspect your landing gear and trailer alignment before pulling. An offset or improperly seated trailer king pin stresses the fifth wheel and is a common trigger for this citation.
- Check your lights before you move. 393.9 (inoperable required lamps) appears in 143 shared inspections in our 90-day data — the most common co-occurring violation. An inspector who stops you for a dark marker light will look at everything else, including your coupling.
- Verify no brake or steering issues exist. 393.47E (slack adjuster defective) and 393.53B (steering system components worn) each appear in over 60 shared inspections from the last 90 days. A thorough pre-trip that catches these prevents an inspection from expanding into a coupling check.
- Confirm you have your periodic inspection documentation. 396.17C (no proof of periodic inspection) appears in 78 shared inspections in our 90-day data. Lack of paperwork signals to an inspector that maintenance may be deferred across the board, putting every system — including your coupling — under closer scrutiny.
- Freightliner, Kenworth, and Peterbilt drivers: These three makes account for the majority of 393.55D2 citations in our database. If you're operating one of these units, your fifth wheel and coupling hardware should be a non-negotiable stop on your pre-trip checklist, every single time.