What 393.55(b) means in plain language
This regulation targets the hardware and methods that physically connect a towed unit to a towing vehicle. When an inspector finds that the coupling devices — think pintle hooks, fifth wheels, drawbars, safety chains, or any other connecting hardware — are in a condition that makes them inadequate for the job, a 393.55(b) citation is the result.
The standard isn't just about whether the connection looks rough. It's about whether the device or method is genuinely defective or otherwise insufficient to safely handle the load and motion of the combination vehicle. Worn locking jaws, cracked drawbar eyes, missing or improperly secured safety chains, and fifth wheel components that don't fully engage all fall within the inspector's scope here.
Put simply: if the thing holding your trailer to your truck is broken, degraded, or rigged in a way that wouldn't hold up under real road conditions, you're looking at this citation.
What our enforcement data actually shows
Across our 13 million+ inspection records, 393.55(b) has generated 2,804 all-time citations, placing it at #460 out of 3,036 FMCSR codes by citation volume. That's a mid-tier enforcement presence — not a top-100 citation, but far from obscure.
The out-of-service picture here is striking: our inspection records show an all-time OOS rate of just 0.0% — only 1 citation out of 2,804 resulted in a vehicle being placed out of service. Compare that to the all-FMCSR average OOS rate of 31.4%, and you get a clear picture: inspectors are writing this violation regularly, but they are almost never pulling drivers off the road for it on the spot. That doesn't mean it's harmless — more on the CSA weight in a moment — but it does mean your immediate operational disruption risk at the roadside is very low.
For recent enforcement activity, the data shows zero citations in the last 90 days and zero in the last 12 months. Enforcement of this specific sub-section has gone quiet in the near term, though the 2,804 all-time citations confirm it has been actively written in the past.
One number you should not ignore: the CSA severity weight for 393.55(b) is 8 out of a possible 10. Even though inspectors rarely put vehicles out of service for this violation, a citation lands hard on your CSA Maintenance BASIC score. A single citation at severity weight 8 can meaningfully shift your percentile, especially at smaller fleets where one inspection carries a lot of statistical weight.
Who gets cited most
The top vehicle makes in our database for 393.55(b) citations tell an interesting story about where inspectors are finding these defects. FORD leads with 208 citations, followed by FRHT at 120, INTL at 84, INTERNATIO at 83, and HINO at 79. The presence of FORD, GMC (69 citations), CHEVROLET (59), ISUZU (57), and DODGE (53) alongside heavy-iron brands like FRHT and Freightliner (73) confirms that this citation is not limited to Class 8 tractors — medium-duty and light commercial vehicles pulling trailers are very much in scope.
On the carrier side, our data shows fleets such as UNITED PARCEL SERVICE INC (USDOT 21800) with 25 citations and VESTIS SERVICES LLC (USDOT 221707) with 10 citations appearing at the top of the all-time list. FEDERAL EXPRESS CORPORATION (USDOT 86876) appears with 9 citations. The presence of large parcel and uniform-service fleets — which run high volumes of medium-duty vehicles pulling small trailers or using tow-away configurations — aligns with the vehicle make distribution noted above.
How severe is this compared to similar codes
To put 393.55(b)'s 2,804 citations in context, look at how other Vehicle Maintenance codes perform in our database.
393.9(a) — Inoperable required lamps has 660,737 citations — roughly 236 times the volume of 393.55(b) — with a 15.4% OOS rate. Lighting violations are the bread and butter of roadside inspections; coupling device defects are comparatively rare but carry a heavier CSA severity weight.
396.3(a)(1) — Inspection/repair/maintenance - general sits at 236,919 citations with a 45.3% OOS rate. That 45.3% figure is the starkest contrast: a general maintenance deficiency under 396.3(a)(1) is nearly ten times more likely to put you out of service than a 393.55(b) coupling device citation. Both can be written on the same inspection, however, so a coupling defect that an inspector views as serious enough to rise to a general maintenance failure can compound quickly.
393.78 — Windshield condition defective shows 157,894 citations and a 0.3% OOS rate — a closer behavioral comparison to 393.55(b)'s near-zero OOS rate. Both are high-volume, low-OOS codes in the maintenance category, but 393.55(b)'s severity weight of 8 makes it a more damaging CSA hit than most windshield violations.
How to avoid it
The vehicle make data — heavy FORD, GMC, CHEVROLET, ISUZU, and DODGE representation — makes clear that drivers of medium-duty trucks pulling utility trailers, liftgate trailers, or dolly tows need to treat coupling inspection as seriously as their Class 8 counterparts. Here's what to check before every trip:
- Inspect the fifth wheel or pintle hook locking mechanism. Manually test that the locking jaw or bail is fully engaged and that there is no lateral play beyond the manufacturer's specification. Do not rely on a visual check alone — tug the trailer with the tractor to confirm positive coupling.
- Check safety chains or cables. They must be crossed under the tongue, attached to a secure point on the towing vehicle, and have enough slack for turns but not so much that they drag. Missing, broken, or improperly hooked chains are a direct path to this citation.
- Examine drawbar eyes, coupler balls, and receiver hitches for cracks, deformation, or wear. On medium-duty vehicles — the FORDs, GMCs, and ISUZUs that dominate this citation list — ball mounts and receiver hitches are common failure points that are easy to overlook during a cursory walk-around.
- Verify that fifth wheel mounting bolts and kingpin are within spec. Loose mounting hardware is a defect that an inspector can flag under 393.55(b) even if the coupling itself closes properly.
- Document your coupling check in your pre-trip log. If you are cited, a documented pre-trip inspection that specifically notes the coupling system — and any corrective action you took — demonstrates good faith and supports a challenge to the violation if the defect was not present or was corrected before departure.
Our inspection records show that the overwhelming majority of 393.55(b) citations — 2,803 out of 2,804 — did not result in an OOS order, meaning drivers were allowed to continue after the citation. But at a CSA severity weight of 8, the citation follows you for 36 months. A few minutes on the coupling system at every pre-trip is the cheapest insurance available.