What 393.9(b) means in plain language
393.9(b) requires that certain required lamps on your truck be operable—specifically, the clearance lamps at the front, side, and rear of your vehicle must function correctly. These lamps help other drivers see your truck in low-light conditions and make your vehicle compliant with visibility standards.
If an inspector finds that one or more of these clearance lamps is burned out, damaged, or not working, you'll be cited for 393.9(b). The violation is straightforward: the lamps must work. There's no gray area about brightness levels or minor cosmetic damage—if the lamp doesn't illuminate as designed, it's a defect.
This is a vehicle maintenance issue, not a paperwork or logbook violation. It's a condition inspectors can observe and test directly during a roadside safety inspection.
What our enforcement data actually shows
Across our 13 million inspection records, 393.9(b) has generated 1,477 all-time citations and ranks #612 out of 3,036 FMCSR codes by enforcement volume. This is a relatively infrequent citation—you won't see it cited as often as major brake or lighting violations.
When cited, 326 trucks were placed out of service and 1,151 were not, giving 393.9(b) a 22.1% out-of-service rate. The all-FMCSR average OOS rate is 31.4%, which means clearance lamp violations are less likely to result in immediate roadside removal compared to the typical enforcement code. This reflects the regulation's structure: a burned-out clearance lamp is a defect requiring repair, but it's not as immediately dangerous as, for example, failed brakes.
Over the last 12 months and last 90 days, our database shows zero citations for this code, suggesting it's either being issued very rarely or that most fleets have resolved the underlying maintenance issues that trigger it.
Who gets cited most
Our inspection records do not include geographic state-level breakdowns for 393.9(b) in the data available to us. However, we can point to the carriers with the highest citation counts for this violation.
Curbside Waste Inc (USDOT 2295992) leads with 7 citations, followed by American Builders & Contractors Supply Co Inc (USDOT 251000) with 6 citations. These numbers reflect historical enforcement patterns across our database and do not imply systemic negligence; they simply indicate which fleets have encountered this citation most frequently in our records.
When we examine vehicle makes cited for 393.9(b), Freightliner trucks account for 319 citations, Kenworth for 170, International for 164, and Peterbilt for 157. This distribution roughly tracks the overall prevalence of these makes in the commercial trucking fleet, suggesting that clearance lamp defects affect all major manufacturers similarly.
How severe is this compared to similar codes
To put 393.9(b) in context, we'll compare it to other vehicle maintenance codes in the same regulatory category.
393.9(a) — Inoperable required lamps has 660,737 citations and a 15.4% OOS rate. This broader lamp code is cited far more frequently than 393.9(b), but when it is cited, drivers are less likely to be placed out of service. The difference suggests that 393.9(a) captures a wider range of lamp defects, some minor.
396.3(a)(1) — Inspection/repair/maintenance - general has 236,919 citations and a 45.3% OOS rate. This is a catch-all maintenance code cited roughly 160 times more often than 393.9(b), and it results in out-of-service placement nearly twice as frequently. That higher OOS rate reflects the severity of general maintenance failures.
396.17(c) — No proof of periodic inspection has 198,331 citations but a 0.0% OOS rate—a paperwork-only violation. Clearance lamp defects, by contrast, are hardware issues that can prompt roadside repair or vehicle quarantine.
How to avoid it
Clearance lamp defects are preventable through routine pre-trip inspection and prompt repair.
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Walk around your truck before every shift. Check the front, both sides, and rear for burned-out or cracked clearance lamps. If a lamp is dark or obviously damaged, report it immediately and do not operate the vehicle until it's repaired.
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Test clearance lamps during darkness or in low-light conditions. A lamp that appears to work in daylight may not illuminate properly at night. Walk around the truck at dusk or dawn and visually confirm all clearance lamps are glowing.
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Replace burned-out bulbs promptly. Keep spare bulbs of the correct type in your truck or ensure your carrier stocks them at the terminal. A burned-out clearance lamp should be replaced before the truck leaves the lot.
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Inspect for cracked or missing lens covers. Even if the bulb works, a cracked lens or missing protective cover can result in a citation. Replace damaged housings before they worsen.
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Check connections and wiring. If a lamp doesn't illuminate despite a new bulb, the issue may be a loose wire or corroded connector. Wiggle connections gently; if the lamp flickers to life, the connection is loose and needs to be secured or cleaned.
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Follow your carrier's maintenance schedule. If your company has a preventive maintenance program that includes lamp inspection and replacement cycles, participate fully. These programs are designed to catch defects before inspectors do.
Clearance lamps are simple systems, but they're essential for vehicle visibility and legally required. A few minutes during pre-trip inspection can prevent a citation and, more importantly, help ensure other drivers can see your truck safely.