FMCSR 393.83G: Exhaust Discharge Violations Explained

Almost certainly not — but it has happened. Across all-time records in our database, 393.83G carries a 1.8% out-of-service rate (478 OOS placements out of 26,513 total citations). That is dramatically lower than the all-FMCSR average OOS rate of 31.4%, so inspectors rarely pull a truck for this violation alone. That said, 478 trucks did get parked, so the risk is not zero. The circumstances that pushed those inspections into OOS territory often involve inspectors exercising discretion when exhaust fumes are actively entering the cab — so if you smell exhaust inside the vehicle, treat the risk as higher than the average rate suggests.

The STATISTICS block for 393.83G does not include a published severity weight, so a specific point value cannot be confirmed from our inspection records. What our data does show is that this code falls under the Vehicle Maintenance BASIC. Any violation in that BASIC scores against both the driver and the carrier, and points recorded within the last 6 months count at 3× the base weight, dropping to 2× between 6 and 12 months. With 17,782 citations recorded in just the last 12 months, this is an actively enforced code — even a low-severity weight accumulates fast if your fleet is seeing repeated hits.

Act on the full inspection report, not just the exhaust citation. Our inspection records show that in the last 90 days, 393.83G appears alongside these violations at high rates on the same inspection:

• 393.9 (Inoperable Required Lamp) — 1,188 shared inspections
• 396.5B (Fuel system leak) — 1,114 shared inspections
• 393.45B2UV (Brake tubing/hoses inadequate) — 1,061 shared inspections
• 396.3A1 (Inspection/repair/maintenance) — 872 shared inspections

Fix the exhaust routing first, then verify lamps, check for fuel leaks, and inspect brake lines before the truck moves again. A fuel system leak co-occurring with a misdirected exhaust discharge is a serious combination. Document every repair with dated invoices.

Relatively low-severity by OOS rate, but high by volume. The 1.8% OOS rate for 393.83G matches the peer code 393.11 (Lighting devices/reflectors, also 1.8%) and is far below the 31.4% all-FMCSR average. However, at 26,513 all-time citations it ranks #105 out of 3,036 FMCSR codes — meaning inspectors cite it constantly. Peer codes in the same Vehicle Maintenance category illustrate the contrast: 396.3(a)(1) carries a 45.3% OOS rate and 393.9(a) hits 15.4%. By OOS standards, 393.83G is mild — but its citation volume means it reliably shows up in SMS scoring and can push a carrier's Vehicle Maintenance BASIC percentile without ever resulting in a parked truck.

Yes, you can submit a DataQs Request for Data Review (RDR) for any roadside inspection violation including 393.83G. Because this is an equipment finding rather than a documentation violation, a successful challenge typically requires evidence that the exhaust system did not discharge forward of or directly below the driver or sleeper compartment at the time of inspection — think dated shop repair orders, photographs showing exhaust outlet position, or a reweigh/re-inspection by the original enforcement agency. The process is free and runs through the FMCSA DataQs portal. Keep in mind that if the inspector's observation is well-documented, the bar for overturning it is higher than it would be for a missing paperwork citation.

Texas dominates enforcement of this code by a wide margin. In our inspection records from the last 180 days, TX logged 6,245 citations — with an OOS rate of 1.8% (112 trucks placed out of service). The next highest was a nationwide US federal enforcement category at 1,875 citations with a 0.0% OOS rate, followed by Arizona at 90 citations and a 0.0% OOS rate. If you run cross-border corridors into or through Texas, this code should be a pre-trip checklist item. One outlier worth noting: New Mexico had only 19 citations in the same period, but every single one resulted in an OOS placement — a 100.0% OOS rate — suggesting inspectors there take a harder line when they do cite it.

Fix it before the next trip. The 90-day citation count stands at 4,115, and the monthly trend in our database shows enforcement has been climbing — from 1,521 citations in August 2025 to 1,777 in March 2026. Inspectors are clearly not overlooking this. While the 1.8% overall OOS rate means most cited trucks kept rolling, the New Mexico and Illinois data tell a different story at the state level (100.0% and 63.2% OOS rates respectively). An exhaust discharge into or below the cab also poses direct carbon monoxide risk to the driver independent of any regulatory penalty, which makes this a safety repair, not just a compliance repair.

Both. Under FMCSA's CSA methodology, Vehicle Maintenance BASIC violations attach to the driver's PSP (Pre-Employment Screening Program) record and simultaneously score against the carrier's SMS BASIC percentile. The driver record follows you for 36 months regardless of whether you change employers. The carrier impact is immediate — our database shows the top cited carriers for 393.83G each accumulated over 70 citations all-time, with JESUS MA VALDEZ GARCIA (USDOT 2534784) leading at 125 citations. Repeated hits concentrate in a carrier's Vehicle Maintenance BASIC and can trigger interventions. Drivers should request a copy of every inspection report and verify it is recorded accurately on their PSP.