What 393.83E means in plain language
This regulation targets where your exhaust exits the truck, not whether the system works. Specifically, on a truck or truck-tractor, the exhaust must discharge from the rear of the cab. If fumes or gases are exiting at any other point along the system — underneath the cab, along the frame rails, or from a damaged mid-pipe — that is what gets you cited under 393.83E.
The concern is practical and safety-driven. Exhaust gases escaping in the wrong place can enter the cab, expose the driver to carbon monoxide, and create fire risks near fuel lines or electrical components. It is not a paperwork violation; it is about where a hot, toxic gas stream is pointed on a moving vehicle.
If you were cited at a port of entry or weigh station, the inspector identified that your exhaust system was venting somewhere other than rearward from the cab structure. That finding, however common it may feel, is documented and tied to your vehicle and your carrier's safety record.
What our enforcement data actually shows
Across our database of 13 million+ inspections, 393.83E has generated 5,247 all-time citations. In the last 12 months alone, our inspection records show 3,532 citations — meaning a significant share of the total enforcement history for this code has occurred very recently. In just the last 90 days, inspectors issued 629 citations under this code.
Nationally, 393.83E ranks #331 out of 3,036 FMCSR codes by citation volume. That places it solidly in the top 11% of all cited codes — it is not a rare or obscure violation. Inspectors know what to look for.
Here is the piece of data that should reduce your immediate stress: the all-time out-of-service rate for 393.83E is 0.2%. Out of 5,247 citations, only 12 vehicles were placed out of service. The other 5,235 were cited and allowed to continue operating. To put that in perspective, the all-FMCSR average OOS rate across all codes is 31.4%. This code runs at a fraction of that average. You almost certainly were not shut down, and the data shows that is the norm.
Looking at the monthly trend in our records, citation volume has been elevated and relatively consistent — ranging from 232 to 396 citations per month over the past year — with OOS placements occurring only sporadically. This is a high-volume, low-OOS-risk code. The citation still matters for your carrier's CSA scores, but you were not at unusual risk of being parked roadside.
Who gets cited most
In the last 180 days, our inspection records show Arizona leading at 64 citations, followed closely by California with 63 citations and Texas with 59 citations. These three states account for a disproportionate share of enforcement activity relative to the national 180-day total of 927 citations.
The OOS-rate variation across these three states is worth noting. Arizona recorded 0 OOS placements out of 64 citations — a 0.0% rate. California recorded 1 OOS placement out of 63 citations, a 1.6% rate. Texas recorded 2 OOS placements out of 59 citations, a 3.4% rate. That 3.4-point gap between Arizona and Texas is material: if you are running lanes through Texas, inspectors there appear somewhat more likely to pull you from service on this violation.
Our data also shows that certain fleets appear frequently in citation counts. TRANSPORTES DE CARGA FEMA SA DE CV (USDOT 1175018) has 43 all-time citations, and TRANSPORTATION AND CARGO SOLUTIONS S DE RL DE CV (USDOT 779973) has 42 all-time citations. The concentration of citations among carriers with cross-border operations is a visible pattern in our dataset and reflects the heavy enforcement activity at ports of entry.
How severe is this compared to similar codes
Compared to other Vehicle Maintenance codes in our database, 393.83E is a relatively minor enforcement event. Consider these peers:
393.9(a) — Inoperable required lamps has 660,737 all-time citations and carries a 15.4% OOS rate. That code is cited 126 times more often than 393.83E and carries an OOS rate roughly 77 times higher.
396.3(a)(1) — Inspection, repair, and maintenance general has 236,919 citations with a 45.3% OOS rate. That is a code where nearly half of all citations result in the vehicle being parked. At 0.2%, 393.83E is in an entirely different risk tier.
393.78 — Windshield condition defective has 157,894 citations and a 0.3% OOS rate — the closest peer in terms of OOS risk, though still cited 30 times more frequently. This comparison shows that 393.83E is genuinely low on the OOS-risk spectrum, even within its own category.
The citation does land on your carrier's safety record and contributes to BASIC scores, but the likelihood of a hard operational consequence — being shut down — is minimal based on our data.
How to avoid it
Our records show that 393.83E rarely appears alone at inspection. The co-occurring violation patterns point directly at what inspectors are focused on when they flag this code. Build these checks into your pre-trip:
- Walk the full exhaust path, not just the stack. Start at the manifold and follow the pipe toward the rear. Look for visible separation, cracks, missing clamps, or sections that have shifted out of position. Any gap in the mid-pipe can become a discharge point that is not at the rear of the cab.
- Check for fuel system leaks at the same time. Our data shows 196 shared inspections between 393.83E and 396.5B-L (fuel system leak). A leaking fuel system combined with misrouted exhaust creates a fire hazard that inspectors treat seriously. Run your hand along fuel lines during pre-trip and look for wet spots or fuel smell under the cab.
- Inspect steering and coupling components. 393.209E-SPSLA (power steering leaking) appeared in 110 shared inspections and 393.55E-B (coupling device defective) appeared in 107. These co-occurring violations suggest that trucks flagged for exhaust routing often have broader maintenance deferred. A thorough pre-trip that catches one will often catch the others.
- Check brake-related components while underneath. 393.47E (slack adjuster defective) co-occurred in 99 inspections. If you are already under the truck tracing exhaust routing, run through the brake hardware on that same pass.
- Know your vehicle make's common failure points. Freightliner leads all-time citations with 1,381, followed by Kenworth at 927 and International at 810. If you operate one of these makes, ask your shop specifically about exhaust clamp and flex-pipe integrity during your next PM service.
- On Freightliner and International models especially, mid-pipe flex joints and bellows sections are known to shift over time. A visual check for soot deposits on the frame or cab underside during pre-trip is a reliable indicator that exhaust is leaking before the rear of the cab.