Violation code

393.9ALTSIR

Lighting - Turn signal - Any inoperative on a unit that is not the rearmost unit

Vehicle Maintenance6Non-OOS· SMS Appendix A v3.20

393.9ALTSIR is a Lighting violation under 49 CFR §393.9ALTSIR. It falls in the Vehicle Maintenance BASIC with a severity weight of 6/10. Nationally it was cited 37,425 times in the last five years, with an OOS rate of 0.7%.

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National roadside inspection stats

as of 9/20/2026

Inspections

35,002

that found this code

Violations

37,425

total written

OOS rate

0.7%

260 OOS

Source: FMCSA roadside inspection data (last 5 years). The OOS rate is the share of these violations that led the officer to mark the driver or vehicle out of service.

Violation group: Lighting
Regulation §: 393.9ALTSIR
Severity weight: 6
Used in SMS: Yes
Status: Active
Updated: 9/20/2026

Last updated September 2026

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Notes

DSMS: Y | Comment: Added in 3.16 | Footnote: This violation was added to SMS with the October 27, 2023 snapshot.

What 393.9ALTSIR means — and how to avoid it

In plain English

In plain terms, 393.9ALTSIR is cited for lighting - Turn signal - Any inoperative on a unit that is not the rearmost unit. It falls under the FMCSA rules on parts and accessories needed for safe operation.

What the inspector checks

•Required lamps present, clean, and working — headlamps, tail, stop, turn, marker
•Reflective sheeting/reflectors intact
•Trailer cord and connections making contact

How to prevent it

✓Walk the lights on every pre-trip (have someone confirm brake/turn)
✓Carry spare bulbs/fuses and swap a dead lamp before rolling
✓Clean lenses and check the trailer plug for corrosion

How it affects your CSA

up to 18 pts (fresh)

Severity 6/10. A fresh citation counts at the 3× time weight — up to 18 points toward the Vehicle Maintenance BASIC — then tapers to 2× after 6 months and 1× after a year, dropping off the score at 24 months.

General guidance from the violation’s FMCSA classification — not legal advice, and not a substitute for the inspector’s findings or 49 CFR.

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Challenging 393.9ALTSIR through FMCSA DataQs

If this violation was written incorrectly, here are the angles trucking-safety managers use to contest it. Playbook: Vehicle Maintenance (general).

Relevant 49 CFR49 CFR § 393.9

Lamps operable, prohibition of obstructions

“All lamps required by this subpart shall be capable of being operated at all times. This section shall not be construed to prohibit motor vehicles being operated with lamps that are momentarily inoperative due to vibration, temperature, or similar transient causes.”

Common ways to challenge this code

Pre-trip inspection showed compliant brakes
The driver's pre-trip DVIR documented compliant brake adjustment and operation. The cited defect arose en route or was misclassified at roadside.
Evidence that wins
- ✓Driver Vehicle Inspection Report (DVIR) from that date
- ✓Repair invoice or shop record
- ✓Post-citation re-inspection certificate (clean)
Momentary failure exception (§393.9)
The required lamp was inoperative only momentarily due to vibration, temperature, or similar transient cause — explicitly exempted under §393.9.
Evidence that wins
- ✓Photograph showing the lamp operable before / after the stop
- ✓Repair invoice if a fuse or bulb was replaced
Tread measurement disputed
The tread depth measurement was taken at a worn point that is not representative, contrary to NHTSA/FMCSA measurement standards.
Evidence that wins
- ✓Independent tread gauge reading from same tire (multiple positions)
- ✓Photograph of the tire with a reference scale
Documented maintenance schedule disproves the defect
Carrier's periodic-inspection records show the cited defect could not reasonably have existed at the time of inspection.
Evidence that wins
- ✓Periodic inspection certificate (§396.17)
- ✓Maintenance work order proximate to inspection date

Common pitfalls — avoid these

⚠DataQs cannot remove a violation simply because the defect was repaired after the stop

⚡ Draft a challenge for 393.9ALTSIR →Read the DataQs guide first

More codes in Vehicle Maintenance

Same BASIC category — ranked by national citation volume

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Other Lighting codes

Codes under the same FMCSA violation group

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Frequently asked questions about 393.9ALTSIR

What does violation 393.9ALTSIR mean?

393.9ALTSIR is the FMCSA roadside-inspection violation code for "Lighting - Turn signal - Any inoperative on a unit that is not the rearmost unit", part of the Lighting group, cited under 49 CFR §393.9ALTSIR.

What BASIC does 393.9ALTSIR affect?

393.9ALTSIR falls under the Vehicle Maintenance BASIC in the FMCSA Safety Measurement System (SMS).

What is the CSA severity weight of 393.9ALTSIR?

393.9ALTSIR carries a severity weight of 6 out of 10. Higher weights indicate violations more closely tied to crash risk, and they count more toward a carrier's Vehicle Maintenance score.

Is 393.9ALTSIR an out-of-service (OOS) violation?

No. 393.9ALTSIR is not an out-of-service violation, so on its own it does not trigger an out-of-service order at the roadside.

How many CSA points does 393.9ALTSIR add to a carrier's score?

The point contribution of 393.9ALTSIR depends on its severity weight (6/10) multiplied by a time weight of 3, 2, or 1 based on how recent the inspection is. You can calculate the exact contribution with the CSA points calculator.

How can a driver prevent 393.9ALTSIR?

Walk the lights on every pre-trip (have someone confirm brake/turn); Carry spare bulbs/fuses and swap a dead lamp before rolling; Clean lenses and check the trailer plug for corrosion.

Can 393.9ALTSIR be challenged through DataQs?

Yes. If you believe 393.9ALTSIR was recorded in error, you can file a Request for Data Review (RDR) through the FMCSA DataQs system with supporting evidence. A successful challenge can remove or correct the violation on your record.

Keep going

CSA points calculator How to challenge a violation Draft a DataQs letter for 393.9ALTSIR Vehicle Maintenance BASIC Carrier CSA lookup CSA glossary

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