What 393.75A3 means in plain language
FMCSR 393.75A3 targets one of the most straightforward tire defects an inspector can identify at the roadside: a tire that has gone flat or is losing air at a rate you can hear. If a tire is visibly deflated or an inspector can detect an audible hiss of escaping air during a walkaround, you're looking at a 393.75A3 citation.
The regulation exists because a flat or rapidly deflating tire isn't just a mechanical inconvenience — it directly affects vehicle stability, braking distance, and load transfer, especially on multi-axle combinations running at highway speed. A tire that sounds like it's leaking air is already compromised, even if it hasn't gone fully flat yet.
The standard doesn't require sophisticated measurement equipment. An inspector walking your unit can identify both conditions with eyes and ears alone, which is a large part of why this code generates the citation volume it does.
What our enforcement data actually shows
The numbers behind 393.75A3 are striking. Across our inspection database, this code has accumulated 43,804 all-time citations, ranking it 72nd out of 3,036 FMCSR codes by citation volume. That puts it well inside the top 2.5% of all cited codes nationwide.
What makes 393.75A3 particularly consequential is its out-of-service rate. Our inspection records show that 40,713 of those 43,804 citations resulted in an OOS order — a 92.9% OOS rate. To put that in context, the all-FMCSR average OOS rate is 31.4%. This code runs nearly three times that average. When an inspector writes 393.75A3, the vehicle almost always stops moving.
Enforcement volume is not slowing down. Over the last 12 months, our database recorded 23,855 citations under this code. In just the last 90 days, 5,627 citations were issued. The monthly trend data reinforces this: citations climbed from 1,028 in April 2025 to 2,388 in March 2026, a pattern that holds across nearly every month in the period. December 2025 through March 2026 all came in above 2,100 citations per month, with January 2026 peaking at 2,367 citations and 2,185 of those resulting in OOS orders.
Who gets cited most
Looking at the last 180 days, three states generate the vast majority of 393.75A3 enforcement activity. Texas leads by a wide margin with 8,410 citations, and 7,586 of those — a 90.2% OOS rate — resulted in vehicles being placed out of service. New Mexico recorded 1,896 citations over the same period with a 100.0% OOS rate, meaning every single 393.75A3 citation issued in New Mexico during this window resulted in an OOS order. North Carolina logged 1,268 citations with a 98.3% OOS rate.
The gap between states is material. Texas and North Carolina are both above 90%, but New Mexico's 100.0% rate versus Texas's 90.2% is a 9.8 percentage point difference — if you're operating in New Mexico, the data suggests inspectors there treat this defect as an automatic OOS condition without exception.
On the carrier side, our data shows fleets such as Swift Transportation Co of Arizona LLC (USDOT 54283) with 147 all-time citations and Federal Express Corporation (USDOT 86876) with 133 citations at the top of the volume list. These are among the highest-mileage fleets in the country, and their presence here reflects the statistical reality that more wheels on the road means more exposure to tire-related inspection events.
How severe is this compared to similar codes
Compared to other codes in the Vehicle Maintenance category, 393.75A3 is an outlier in terms of OOS consequences. Consider 393.9(a), covering inoperable required lamps, which has 660,737 all-time citations — more than fifteen times the volume of 393.75A3 — but carries only a 15.4% OOS rate. Inspectors cite lamp violations frequently but send the vehicle down the road most of the time. That is not how 393.75A3 works.
Look at 396.3(a)(1), the general inspection, repair, and maintenance code, which shows 236,919 citations and a 45.3% OOS rate. That rate is meaningfully higher than the all-FMCSR average, but it still sits 47.6 percentage points below 393.75A3's 92.9% rate. Even 393.78, covering defective windshield condition, which appears alongside 393.75A3 in 656 shared inspections over the last 90 days, carries only a 0.3% OOS rate across its 157,894 citations. The tire defect code operates in a different enforcement tier entirely.
How to avoid it
The pre-trip inspection is your primary defense. Every co-occurring violation pattern and vehicle make distribution in our data points back to the same root cause: deferred or insufficient pre-trip attention to tires and the mechanical systems adjacent to them. Here's what to act on before you pull out:
- Walk every tire before departure. Visually inspect all tires for obvious deflation or sidewall bulging. Don't assume a tire looks fine from the cab — step out and look at drive axles, steer axles, and trailer axles individually.
- Listen during your walkaround. An audible air leak is a 393.75A3 citation waiting to happen. If you can hear escaping air during your pre-trip, an inspector will hear it too. Trace the sound to a valve stem, bead seal, or tread puncture before you roll.
- Check valve stems and caps. Missing or damaged valve caps allow debris to compromise valve cores, which are a common source of slow leaks that accelerate into audible leaks under load and heat.
- Inspect brake hardware at the same time. Our co-occurrence data shows 393.47E (slack adjuster defective) appeared alongside 393.75A3 in 426 shared inspections in the last 90 days, and 393.45B2UV (brake tubing and hoses) appeared in 439. Brake and tire systems share inspection proximity — if you're at the wheel end anyway, check the slack adjusters and visible air lines.
- Check for fuel and air system leaks together. Code 396.5B (fuel system leak) co-occurred in 453 shared inspections. A vehicle that has a fuel leak and a tire air leak is a vehicle that didn't get a thorough pre-trip. Use a systematic axle-to-axle walk, not a quick glance.
- Pay extra attention on Freightliner and Kenworth equipment. Our database records 14,567 citations on FRHT vehicles and 6,144 on KW platforms — together accounting for the largest share of all 393.75A3 events. These are high-population tractors, but their dominance in this code's data means if you're in one, your pre-trip tire check carries real statistical weight.
- Don't defer a soft tire to the next stop. A tire that's slightly low at dispatch will be audibly leaking by the first weigh station. Fix it before you leave the yard.