Section 393.9 requires that all lamps required by 49 CFR Part 393, Subpart B be operable at all times. This includes head lamps, tail lamps, stop lamps, turn signals, marker lamps, identification lamps, and clearance lamps — the precise list depends on the type of vehicle.
Why it's so commonly cited
A single inoperative marker lamp on a 53-foot trailer generates a §393.9 violation in seconds during a Level I or Level II inspection. Mud, road grime, vibration, and corrosion all conspire to take lamps out of service between trips.
Severity weight and OOS
The severity weight is 6 in the Vehicle Maintenance BASIC. A required lamp inoperative on the front or rear during night operation is grounds for an out-of-service order under the North American Standard Out-of-Service Criteria.
How to prevent it
- Pre-trip inspection should include all lamps with the four-way and brake pedal applied (have someone walk the vehicle, or use a reflective wall).
- Stock spare bulbs and fuses in the cab.
- Check connectors at the trailer plug after every disconnection — corrosion is the leading cause of intermittent failures.
- Log the inspection on the DVIR. If a lamp fails between inspections, log the repair.
How Roadworthy HQ helps
An inoperable-lamp citation shows up in Roadworthy HQ as part of the inspection it came from, not as a record of its own: the app does not store individual violation codes. Log the roadside inspection on the vehicle's Inspections tab: date, state, level, driver, the number of violations, and whether it was out-of-service. For an out-of-service inspection the 15-day §396.9(d)(3) repair-certification countdown stays on that tab until you enter the certification date. The rule's 15 days cover every violation on the report, not only out-of-service ones, so for a non-OOS inspection that date is yours to track. The repair itself goes in the vehicle's maintenance log: date, type, what was done, who did it, and cost. DVIRs are logged per vehicle with the defect described in your own words, and a defect marked safety-affecting that is logged without a repair certification sends a critical alert.