What 393.83(b) means in plain language
Your citation for 393.83(b) concerns the routing of your truck's exhaust system. Specifically, the regulation requires that your exhaust outlet does not discharge directly below the fuel tank or filler pipe location on your vehicle.
Why does this matter? Fuel tank and filler pipes are vulnerable areas. If exhaust gases or hot residue exit from underneath those components, you risk fire, fuel line damage, or ignition hazards—especially during refueling or in accident conditions. The rule exists to keep the exhaust path physically separated from fuel infrastructure, a straightforward safety isolation.
This is a maintenance and equipment issue, not a driver conduct violation. It reflects the condition of your vehicle's installed exhaust system.
What our enforcement data actually shows
Across our 13 million+ inspection records, 393.83(b) has generated 144 all-time citations in our database. In the last 12 months and last 90 days, we recorded zero citations for this code, indicating it is encountered rarely in roadside enforcement.
When cited, 393.83(b) resulted in out-of-service placement in 25 of 144 cases, yielding a 17.4% OOS rate. That is substantially lower than the all-FMCSR average OOS rate of 31.4%, meaning inspectors are more likely to let you continue your haul with a warning or repair order rather than ground you immediately. Nationwide, 393.83(b) ranks #1315 out of 3,036 FMCSR codes by citation frequency, placing it in the lower-enforcement tier.
Who gets cited most
Our inspection records do not provide state-level breakdowns specific enough to rank the top three states by count in this dataset. However, we observe that the violation has been documented across multiple carriers. Walter Moore (USDOT 2475064) appears in our records with 3 citations for 393.83(b), followed by Autotransportes Varela Davila SA de CV (USDOT 1716824) and Oscar Guillermo Juraidini Silva (USDOT 2511762), each with 2 citations. The concentration is spread; no single carrier dominates enforcement, and the low volume overall indicates this is not a systemic fleet issue for any operator.
How severe is this compared to similar codes
393.83(b) sits in the Vehicle Maintenance category alongside codes that address lamps, inspection documentation, brake components, and windshield condition. To contextualize its severity:
393.9(a) — Inoperable required lamps has accumulated 660,737 citations with a 15.4% OOS rate. That code is cited roughly 4,600 times more frequently than 393.83(b), though its OOS rate is comparable.
396.3(a)(1) — Inspection/repair/maintenance general carries 236,919 citations and a 45.3% OOS rate, more than three times higher than 393.83(b). Maintenance defects flagged under the broader inspection standard are far more likely to ground a vehicle.
393.78 — Windshield condition defective has 157,894 citations but only a 0.3% OOS rate. Like 393.83(b), it is a relatively minor citation that rarely triggers immediate OOS status.
Your citation is on the lenient end of the maintenance enforcement spectrum. Inspectors treat exhaust routing as a fixable issue rather than an immediate safety-critical failure.
How to avoid it
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Pre-trip inspection of exhaust routing: Walk under the back of your truck during your pre-trip and visually trace the exhaust pipe. Confirm it exits to the side or rear of the vehicle, never downward directly beneath the fuel tank or filler opening. If you cannot see the filler pipe location on your unit, ask your fleet or mechanic to mark it clearly so you know which areas to avoid.
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Check for heat damage or cracks: If the exhaust outlet is bent, cracked, or misaligned, it may have shifted downward over time. Look for corrosion stains, soot accumulation, or physical contact marks on nearby fuel lines or tank surfaces. These are early warnings.
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Verify exhaust bracket and hanger integrity: Exhaust systems are held in place by brackets and rubber hangers. If those fail, the exhaust pipe sags and can drop below the fuel tank. During pre-trip, give the exhaust system a gentle shake (engine off, exhaust cool) to confirm it is secure and does not move excessively.
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Address rust and vibration: Heavy-duty trucks with high mileage sometimes see exhaust pipe rust that weakens the metal, or worn engine mounts that allow greater vibration. If your truck is older or has been through corrosive conditions, request a full exhaust system inspection from your mechanic before it fails at roadside.
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Know your fuel tank location: If you are driving a vehicle unfamiliar to you (rental, borrowed, or new assignment), ask the dispatcher or fleet maintenance team to point out where the fuel tank and filler pipe are located. This takes 30 seconds and helps you spot anomalies instantly during your walk-around.