What 393.80A means in plain language
FMCSR 393.80A targets problems with the exhaust system on a commercial motor vehicle. Specifically, it covers three failure modes: an exhaust system that is leaking at any point along its path, one that isn't properly secured to the vehicle's frame or body, and one that discharges exhaust gases at a point below the vehicle's floor level.
The concern behind the rule is straightforward — exhaust gases contain carbon monoxide, and any arrangement that lets those gases seep into the cab or sleeper berth creates a serious health and safety hazard for the driver. A loose or rattling exhaust pipe also risks contacting fuel lines, wiring, or tires as the vehicle moves.
For enforcement purposes, an inspector can cite 393.80A if they observe visible soot staining around joints or clamps, if a pipe is hanging, missing a hanger bracket, or if the termination point of the exhaust is oriented in a way that routes gases underneath the floor of the cab.
What our enforcement data actually shows
Across our database of 13 million+ roadside inspections, 393.80A has generated 3,335 all-time citations. Of those, only 14 vehicles were placed out of service — producing an OOS rate of just 0.4%. That number is dramatically lower than the all-FMCSR average OOS rate of 31.4%, meaning that while inspectors will write this citation, they almost never consider the condition serious enough to park the truck on the spot.
The code is also confirmed as OOS-ineligible, which is consistent with that 0.4% figure — the rare exceptions in the data likely reflect inspectors applying judgment in unusually severe cases or bundling with other defects.
Enforcement volume is active and increasing. Our inspection records show 1,755 citations were issued in just the last 12 months, and 330 in the last 90 days alone. The monthly trend data shows the code running consistently above 130 citations per month through late 2025 and into 2026. The peak month in the dataset was July 2025, with 181 citations and 4 OOS events. This is not a rarely-enforced technicality — inspectors are actively writing it.
Nationally, 393.80A ranks #414 out of 3,036 FMCSR codes by all-time citation volume, placing it in the top 14% of all codes for enforcement frequency.
Who gets cited most
Looking at the last 180 days, the top three states by citation count are Georgia (117 citations), Washington (60 citations), and a federal/US-jurisdiction category (59 citations). New Jersey and New York follow closely with 58 and 56 citations respectively.
The OOS-rate variation across those top states is minimal and largely immaterial — Georgia, Washington, and New York all sit at 0.0% OOS. New Jersey is the only top-five state with any OOS activity, posting a 1.7% rate off 1 OOS event out of 58 citations. That's a small sample, but it signals that New Jersey inspectors have occasionally been willing to park a vehicle for this violation when conditions warranted it.
Among carriers, our data shows fleets such as Federal Express Corporation (USDOT 86876) with 27 all-time citations and J B Hunt Transport Inc (USDOT 80806) with 16 citations appearing at the top of the citation list. The presence of large national carriers in this data reflects simple exposure — more trucks on the road means more inspections, and even well-maintained fleets accumulate citations on high-volume codes.
How severe is this compared to similar codes
To put 393.80A in context, compare it against peer codes in the Vehicle Maintenance category.
393.9(a), covering inoperable required lamps, has been cited 660,737 times in our database — nearly 200 times the volume of 393.80A — and carries a 15.4% OOS rate. That code is far more frequently enforced and far more likely to put a driver on the side of the road.
396.3(a)(1), the general inspection, repair, and maintenance code, has 236,919 citations and a 45.3% OOS rate — meaning nearly half of all vehicles cited under that code get parked. That's a fundamentally different risk profile than 393.80A's 0.4%.
393.78, the windshield condition code, is closer to 393.80A in character — 157,894 citations and a 0.3% OOS rate, essentially the same low-consequence enforcement pattern. Both codes are written regularly but rarely result in an OOS order on their own.
The bottom line: a 393.80A citation carries a CSA severity weight of 4, which means it counts against your Safety Measurement System score but is not in the same risk tier as brake or steering defects. It is a citation you want to prevent and fix quickly, but it is unlikely by itself to end your day at the roadside.
How to avoid it
The co-occurring violation pattern in our inspection records tells a clear story: 393.80A rarely shows up alone. It clusters with hood security issues, fuel system leaks, cab and body component defects, and lamp failures. Vehicles cited for this code are typically showing multiple signs of deferred maintenance. Your pre-trip is the right place to stop this.
- Walk the exhaust system end to end. Start at the manifold and work toward the stack or outlet. Look for soot staining, black streaking, or oily residue around joints, flex sections, and clamps — those are signs of a leak. Give each hanger bracket a firm tug to confirm it's secure and not cracked.
- Check the termination point. Confirm the exhaust outlet directs gases away from and not beneath the floor of the cab or sleeper. This is especially relevant on vocational trucks or vehicles with non-standard body configurations.
- Look for loose or missing clamps. A clamp that was tight last week can work loose under vibration. Pay attention to any new rattles or exhaust smell in the cab during startup — those are your early warning signs.
- Pair this with a fuel system check. Across our last 90 days of data, 396.5B-L (fuel system leak) appeared in 65 of the same inspections as 393.80A. A fuel leak and an exhaust leak in proximity is a fire risk. Check fuel lines, connections, and look for wet spots under the chassis.
- Check your hood latch and cab body components. 393.203C-CBP (hood not securely fastened) appeared in 77 shared inspections in the same 90-day window. Inspectors who spot one exterior maintenance issue will look for others. A thorough walkaround that catches the hood latch also protects you from the exhaust citation.
- Know your vehicle. Freightliner platforms account for 669 all-time citations under this code, the highest of any make in our data, followed by International with 303 and Volvo with 220. If you're running any of these trucks, pay extra attention to exhaust hanger condition, particularly in the mid-chassis area where road debris and flex stress tend to cause bracket fatigue first.