What 393.9A-LSLI means in plain language
When an inspector writes up 393.9A-LSLI, the core finding is straightforward: your commercial motor vehicle was on the road with one or more required lamps that weren't working. Required lamps aren't optional equipment — they're the lights the federal regulations mandate be operational any time you're moving, covering everything from headlamps and tail lamps to clearance lights, marker lights, and turn signals depending on your vehicle type and configuration.
The key word in this violation is "required." Not every dark bulb on a truck qualifies — the lamp has to be one that federal rules specifically demand be functional. That said, inspectors are trained to know exactly which lamp positions are mandatory, and at roadside, the burden falls on you and your equipment to meet that standard.
This is a Vehicle Maintenance violation, meaning it reflects on the mechanical readiness of your equipment. Even though a burned bulb might feel like a minor inconvenience, it lands in your CSA record and affects your carrier's Safety Measurement System scores.
What our enforcement data actually shows
Across our inspection records, 393.9A-LSLI has generated 44,965 all-time citations, making it the 70th most-cited code out of 3,036 FMCSR codes in our database — that's a significant enforcement presence. In just the last 12 months, inspectors issued 27,568 citations under this code, and 5,712 of those came in the last 90 days alone, signaling that enforcement activity remains active and consistent.
The out-of-service picture is notably more forgiving than most violations. Our inspection records show a 2.7% OOS rate all-time — meaning 1,233 vehicles were placed out of service out of 43,732 that were not. To put that in perspective, the all-FMCSR average OOS rate across all codes is 31.4%. This code sits dramatically below that average, which is consistent with its OOS-ineligible classification. In most cases, you'll receive the citation and be sent on your way, but the violation still attaches to your CSA profile.
Looking at the monthly trend in our database, citation volumes peaked between July and September 2025, with 2,748 citations in July 2025 and 2,700 in August 2025. Volume moderated through the winter months before climbing again to 2,631 in March 2026. This pattern suggests inspectors are consistently active on lamp compliance throughout the year, with no meaningful seasonal reprieve.
Who gets cited most
Among states generating citations in the last 180 days, California leads with 1,285 citations — and it stands apart from the rest of the field in one important way. California posted a 14.2% OOS rate on this code, with 183 vehicles placed out of service. Every other top state in our data recorded a 0.0% OOS rate over the same period. That's a gap of more than 14 percentage points, which is material and worth noting if you operate routes into or through California — inspectors there appear to be applying OOS criteria more broadly or in combination with other conditions.
Second is the federal/national inspection category (coded as "US") with 749 citations and 0 OOS placements, followed by New York with 626 citations and a 0.0% OOS rate. Missouri recorded 530 citations and Florida 471, both also at 0.0% OOS.
On the carrier side, our data shows fleets such as Federal Express Corporation (USDOT 86876) with 94 all-time citations and Evans Delivery Company Inc (USDOT 38111) with 87 citations appearing at the top of the volume list. High citation counts at large fleets reflect the sheer scale of their operations and the number of units on the road, not necessarily a disproportionate defect rate.
How severe is this compared to similar codes
It helps to see 393.9A-LSLI in context alongside peer codes in the Vehicle Maintenance category. The broader 393.9(a) — Inoperable required lamps parent code — has accumulated 660,737 citations in our database with a 15.4% OOS rate. That much higher OOS rate across the parent code family tells you that lamp violations as a whole carry real OOS risk in certain configurations; 393.9A-LSLI's 2.7% rate reflects a specific subset where inspectors are generally not finding grounds to park the vehicle.
Compare that to 396.3(a)(1) — Inspection/repair/maintenance (general) — which carries 236,919 citations and a 45.3% OOS rate. That code represents a much harder enforcement outcome. Meanwhile, 396.17C-PI (No proof of periodic inspection) has 212,081 citations in our data but a 0.0% OOS rate, similar in structure to 393.9A-LSLI — high volume, low OOS. The pattern is clear: 393.9A-LSLI is a high-frequency, low-OOS violation, but don't let the low OOS rate make you complacent. Every citation adds CSA weight.
How to avoid it
The co-occurring violation data in our inspection records provides a clear map of what else inspectors find when they write up 393.9A-LSLI. In the last 90 days, 973 inspections with this violation also carried 396.17C-PI (no proof of periodic inspection), and 609 shared inspections included a tire inflation defect. That tells you inspectors finding lamp issues are also digging into maintenance documentation and tire condition. A thorough pre-trip isn't just about the lamp itself — it's about the whole picture the inspector sees.
- Walk every lamp position before you roll. Check headlamps, tail lamps, clearance lights, marker lights, brake lights, and turn signals. Don't assume a lamp that worked yesterday still works today — filaments fail without warning.
- Carry spare bulbs and fuses for your most common lamp positions. Freightliners account for 7,532 all-time citations under this code in our database, Kenworths for 3,147, and Peterbilts for 3,045. Know the bulb specs for your specific unit and have replacements accessible.
- Check your trailer lighting connections at every pre-trip and every drop-and-hook. The co-occurrence data shows that turn signal and tail lamp issues (393.9A-LTSI and 393.9A-LTSIR) appeared in 1,694 and 1,587 shared inspections respectively in the last 90 days — trailer connection integrity is a primary source of these failures.
- Verify your periodic inspection documentation is current and in the cab. With 973 co-occurring 396.17C-PI violations in 90 days, inspectors writing lamp citations are clearly also checking inspection records. A missing annual inspection report turns one problem into two.
- Inspect the windshield and coupling hardware before departure. Our data shows 519 inspections also carried a windshield defect citation and 465 carried a coupling device violation alongside 393.9A-LSLI. Inspectors conducting thorough lamp checks are clearly doing full vehicle walk-arounds — your pre-trip should match that level of scrutiny.