What 393.80 means in plain language
FMCSR 393.80 covers the condition and security of your truck's exhaust system. An inspector will cite you for this violation if they observe that your exhaust system is leaking, not properly secured to the vehicle, or discharging exhaust gases below the floor level of your truck.
In practical terms, this means your muffler, tailpipe, or connecting exhaust components are either visibly damaged and losing exhaust, hanging loose or rattling because mounting brackets are broken or missing, or positioned so low that exhaust is being pushed downward underneath the truck bed instead of safely away from the vehicle. Any of these conditions triggers a citation.
The regulation exists for two main reasons: safety (loose or improperly mounted exhaust can catch fire or cause structural damage) and emissions compliance (exhaust discharge position matters for both air quality and vehicle integrity).
What our enforcement data actually shows
Across our 13 million+ inspection records, 393.80 has been cited 1,693 times all-time, making it rank #572 of 3,036 FMCSR codes by citation volume. In the last 12 months, inspectors issued 106 citations for this violation; in the last 90 days, 23 citations.
Here's the critical number for your situation: the out-of-service (OOS) rate for 393.80 is 0.4% all-time. That means only 7 trucks out of 1,686 cited were actually placed out of service for this violation. For context, the all-FMCSR average OOS rate is 31.4%, so 393.80 is far below the average—inspectors almost never ground a truck for exhaust system defects alone. A citation is a compliance mark, but it rarely results in immediate removal from service.
The monthly trend over the last year shows enforcement hovering between 3 and 13 citations per month, with February 2026 seeing a spike to 13 citations and recent months (January–March 2026) ranging from 3 to 10.
Who gets cited most
Our inspection records show citations concentrated in three states over the last 180 days. Texas leads with 18 citations (0.0% OOS rate), followed by Illinois with 14 citations (0.0% OOS rate), and New Mexico with 9 citations (0.0% OOS rate). North Carolina, Iowa, and Kentucky round out the top six, each with low single-digit counts. Across all top states, the OOS rate is uniformly 0.0%, meaning no trucks were taken out of service for 393.80 in any of these jurisdictions recently.
By carrier, our all-time data shows fleets such as New Jersey Transit Corporation with 12 citations and Western Express Inc. with 9 citations. United Parcel Service Inc., Federal Express Corporation, and J B Hunt Transport Inc. each appear with 5 or 7 citations. These numbers reflect exposure and inspection frequency; they do not imply systemic negligence.
How severe is this compared to similar codes
FMCSR 393.80 sits in the Vehicle Maintenance category, alongside several other lighting, visibility, and structural codes. For comparison:
393.9 (Inoperable Required Lamp) has been cited 180,097 times with a 6.9% OOS rate—dramatically higher volume and a 17.25-fold greater OOS rate than 393.80.
393.78 (Windshield Condition Defective) has 157,894 all-time citations but only a 0.3% OOS rate, similar to 393.80 in severity and enforcement outcome.
396.3(a)(1) (Inspection/Repair/Maintenance - General) is the highest-volume peer code at 236,919 citations with a 45.3% OOS rate, indicating that general maintenance defects are cited far more often and are more likely to result in out-of-service placement.
The takeaway: 393.80 is a low-frequency violation with minimal out-of-service risk, but it remains enforceable and signals a maintenance gap.
How to avoid it
Our co-occurring violation data reveals patterns that can guide your pre-trip inspection. When 393.80 appears in the same roadside inspection, it frequently co-occurs with:
- Inoperable lamps and turn signals (393.9, 393.9TS) — 12 shared inspections in the last 90 days
- General inspection and repair defects (396.3A1) — 7 shared inspections
- Brake and structural issues (393.47A, 393.45B2UV, 393.201A) — 6 shared inspections combined
- Fuel system leaks (396.5B) — 5 shared inspections
This tells us that exhaust system failures often cluster with other deferred maintenance items.
Vehicle-make data shows Freightliner (FRHT) dominates the citation count at 203, followed by Peterbilt (PTRB) at 74 and Utility trailers (UTIL) at 59, reflecting their prevalence in the fleet, but exhaust defects occur across all major makes.
Concrete pre-trip actions to prevent 393.80:
- Walk around and under the entire exhaust system. Look for visible cracks, rust holes, or separation in the muffler, tailpipe, and connecting tubes. Run your hand underneath the tailpipe outlet to confirm it hangs below floor level and hasn't sagged or bent upward.
- Check all exhaust mounting brackets and clamps. Shake the muffler and tailpipe gently by hand. If they move or rattle, tighten or replace broken brackets immediately. Loose exhaust will fail inspection.
- Inspect for active leaks. Run the engine briefly during a cold start and observe whether any visible exhaust smoke or soot escapes from joints, tears, or mounting points other than the tailpipe outlet.
- Schedule maintenance when brakes, suspension, or frame components are serviced. Our data shows 393.80 often appears alongside brake and structural defects, suggesting these work activities can dislodge or damage exhaust systems. Request that the shop verify exhaust security as part of any major repair.
- Pay attention to hot spots or discoloration on the frame, fuel tank, or undercarriage directly above or near the exhaust. This suggests heat stress or a leak in progress.
Because the OOS rate is so low (0.4%), a citation for 393.80 is unlikely to take your truck out of service immediately. However, it will add points to your BASIC safety profile and flag a maintenance obligation. Fix it promptly to avoid accumulating violations.