What 393.9B-LHWS means in plain language
Hazard warning signals—the lights that flash when you activate your hazard flashers—need to be clearly visible to other drivers. This citation means an inspector found one or more of those lights blocked, covered, or otherwise obscured so they can't be seen properly.
Obscuring these lights defeats their purpose: alerting nearby vehicles that you've broken down, are moving slowly, or pose a temporary hazard. Whether the obstruction came from mud, ice, a loose cover, cargo shift, or accumulated road debris, the result is the same from a safety standpoint. Other drivers can't see your warning, and that increases the risk of a rear-end collision.
This is a vehicle maintenance violation, not a brake or structural defect. It's fixable on the spot in most cases—a quick cleaning or adjustment—which is why inspectors won't place your truck out of service for it.
What our enforcement data actually shows
Across our 13 million roadside inspection records, we've documented 222 all-time citations for code 393.9B-LHWS. In the last 12 months, that number was 122, and in the last 90 days, 24 citations. This code ranks #1190 out of 3,036 FMCSR codes by citation frequency—making it a relatively uncommon violation.
What's most important: the out-of-service rate for 393.9B-LHWS is 0.0% across all 222 citations in our database. Not a single truck was placed out of service for this violation. That's dramatically lower than the all-FMCSR average of 31.4% OOS rate. Inspectors treat obscured hazard lights as a correctable defect, not a safety emergency that requires immediate removal from the road.
The citation rate has held steady over the last 12 months, averaging about 10 per month with no sharp spikes or declines. October 2025 saw the highest monthly count at 14 citations.
Who gets cited most
Our inspection records show citations for obscured hazard lights are spread across the country, but three states account for the largest share in the last 180 days:
- Georgia: 7 citations (0.0% OOS rate)
- Oregon: 4 citations (0.0% OOS rate)
- South Carolina: 4 citations (0.0% OOS rate)
Minnesota, Maryland, Kansas, Pennsylvania, New York, Utah, and Massachusetts also appear in the top 10. None of these states show variation in OOS rates—all are at 0.0%, consistent with the national pattern.
By carrier, our data shows fleets such as New Prime Inc. with 3 citations and Containerport Group Inc. with 3 citations across their operations. Several other carriers including RB & Sons, United Parcel Service Inc., and others have recorded 2 citations each. These numbers reflect the size and mileage of these operations rather than any systemic issue.
How severe is this compared to similar codes
Obscured hazard lights sit at the low end of severity within vehicle maintenance violations. Consider the contrast:
- 393.9(a) — Inoperable required lamps: 660,737 citations with a 15.4% OOS rate. An inoperable lamp is often worse than an obscured one because cleaning or a minor adjustment won't fix it; you may need parts replacement.
- 393.11 — Lighting devices/reflectors: 179,734 citations with a 1.8% OOS rate. This broader category includes reflector and lighting issues and carries a slightly higher OOS risk than 393.9B-LHWS.
- 393.78 — Windshield condition defective: 157,894 citations with a 0.3% OOS rate. Like 393.9B-LHWS, windshield defects are usually correctable on the spot.
Obscured hazard lights are rarely an out-of-service issue because they're almost always fixable immediately—a wipe, adjustment, or removal of debris.
How to avoid it
Most citations for obscured hazard lights stem from neglect during pre-trip inspections or from environmental accumulation over a few days. Prevent this violation with these concrete actions:
- Walk all four corners of your truck during pre-trip. Your hazard lights are typically mounted on the sides and rear. Inspect them for mud, salt, ice, condensation, or any covering that blocks the lens.
- Clean light covers after winter weather or mud. Road spray and winter salt accumulate fast. Use a rag or soft brush—hazard light lenses are plastic and can scratch. A 30-second wipe can prevent a citation.
- Check that no cargo covers or tarps have shifted over the lights. If you're hauling a covered load, make sure straps or ties haven't worked loose and draped over any lighting.
- Look for loose trim or bumper damage. A loose bumper cover, fender, or side panel can creep upward and obscure a hazard light. Tighten or remove it before rolling.
- Test your hazards in daylight if parked indoors. Activate them for a few seconds and walk around. You'll immediately see if any lens is cloudy, fogged, or blocked—and you can fix it before an inspection.
Freightliner trucks account for 52 of all-time citations in this code, followed by Kenworth (17) and International (16). If you operate one of these makes, pay extra attention to the mounting hardware and trim around the lights, as they may be more prone to accumulation or shifting based on the numbers.