What 393.9B-LIL means in plain language
Identification lamps are the marker lights mounted on the front corners, rear corners, and sides of your truck. These lights help other drivers see the full width and length of your vehicle, especially at night or in poor visibility. When an inspector cites you for 393.9B-LIL, they've found that one or more of these lamps is obscured—covered, blocked, or otherwise hidden from view by mud, damage, or placement of equipment.
Obscured identification lamps are a visibility hazard. If your truck's outline isn't clearly marked, other drivers may misjudge where your vehicle ends, which increases the risk of lane-change accidents, merges, and side-impact collisions. This is a maintenance violation, not a safety defect that will yank you off the road immediately.
What our enforcement data actually shows
Across our 13 million roadside inspection records, 393.9B-LIL has generated 1,554 all-time citations, with 912 in the last 12 months and 172 in the last 90 days. This code ranks #594 out of 3,036 FMCSR codes by citation volume—moderate enforcement pressure, but steady.
The most important number: out of 1,554 citations ever issued for obscured ID lamps, zero trucks were placed out of service. The OOS rate is 0.0%, significantly lower than the all-FMCSR average of 31.4%. This tells you that inspectors treat obscured identification lamps as a correctable defect, not an imminent hazard. You will receive a citation, but you will not be sidelined at the roadside.
In the last 90 days, we see an average of about 57 citations per month. Enforcement has remained relatively stable over the past year, ranging from 30 citations in April 2025 to 102 in May 2025, indicating this violation is consistently flagged during inspections.
Who gets cited most
Our inspection records show California leads with 42 citations in the last 180 days, followed by Arizona with 29 and Florida with 27. New York, Wisconsin, and Pennsylvania round out the top tier with 24, 20, and 19 citations respectively. All five states maintain a 0.0% OOS rate, confirming this violation is enforced uniformly as a correctable maintenance item nationwide.
Across all-time data, our records indicate fleets such as LADA TRANS INC with 6 citations and BFI WASTE SERVICES LLC with 5 citations have encountered this violation. The presence of waste services carriers suggests that operation in urban environments with tight routes and frequent stops may increase exposure to lamp damage and mud accumulation.
How severe is this compared to similar codes
Identification lamps fall in the broader lighting defect category. The most frequently cited peer code is 393.9(a)—Inoperable required lamps—with 660,737 citations and a 15.4% OOS rate. That violation is far more serious because inoperable lamps represent a complete loss of function; obscured lamps are a visibility degradation. The difference in OOS rates reflects this: inoperable lamps trigger out-of-service removals roughly 1 in 7 times, while obscured lamps never do.
Another close peer is 393.11—Lighting devices/reflectors—with 179,734 citations and a 1.8% OOS rate. That code covers a wider range of lighting and reflector defects, so its OOS rate is higher than 393.9B-LIL but still rare. A third comparison is 393.78—Windshield condition defective—at 157,894 citations and 0.3% OOS rate, a structural defect that, like obscured lamps, is treated as correctable.
How to avoid it
Before every shift, walk around your truck and check all marker lights. This is a pre-trip inspection requirement, and it takes two minutes. Look at the front corners, rear corners, both sides, and the mid-trailer markers if you're pulling a trailer.
Clean mud, road salt, and debris off lamps immediately after dirty conditions. Many obscured lamp citations occur after rain, snow, or unpaved-road operation. If you notice caking or buildup, stop at a truck wash or use a hose before the next scale.
Inspect lamps for damage. Cracks, broken housings, and misalignment block light output. If a lamp is damaged, report it to dispatch or your fleet manager so it can be repaired before the next inspection.
Secure or remove any aftermarket equipment mounted near lamps. Our inspection records show that obscured lamp citations sometimes co-occur with other maintenance gaps. Ensure grille guards, air deflectors, or mud flaps aren't blocking marker light sight lines.
Pay special attention if you operate in high-debris environments. Our data shows California, Arizona, and Florida account for a significant share of citations. If you run those routes regularly or haul waste, aggregate, or construction materials, inspect lamps more frequently.
Check your vehicle's maintenance log. Our records indicate that in the last 90 days, obscured identification lamps appeared alongside 45 co-occurrences of operating while fatigued or ill (392.2-SLLSR) and 30 co-occurrences of missing periodic inspection proof (396.17C-PI). This suggests that some cited drivers had already accumulated other defects. A consistent pre-trip routine prevents stacking violations.