FMCSA Violation Code

393.79 — Defroster/defogger inoperative

49 CFR 393 • Vehicle Maintenance BASIC • Severity 4/10

Out-of-service eligible Vehicle citation CSA weight 4

OUT-OF-SERVICE eligible

Code

393.79

CFR section

49 CFR 393

BASIC

Vehicle Maintenance

Severity

4/10

Out-of-Service

Yes

Unit type

Vehicle

What this violation means

Front-windshield defroster doesn't clear fog or frost. OOS in inclement weather conditions. 4 SMS points.

How often this is cited (last 24 months)

In the last 24 months, 393.79 was cited 3,718 times at roadside inspections against 2,672 carriers, and under 0.1% of those citations were out-of-service violations. It ranks #31 among the violation codes in our records by citation count. Most recent citation on record: Nov 4, 2026.

Why this gets cited

Failed HVAC blend door. Refrigerant low (modern trucks use AC for defrost). Blower motor failure.

How to fix / prevent

HVAC service. Don't drive in winter weather with a non-working defroster — major safety issue.

Out-of-service criteria

Yes — this violation IS out-of-service eligible. When an inspector finds 393.79 during a Level 1, 2, or 3 inspection, they can place the Vehicle OOS using the North American Standard Out-of-Service Criteria. OOS means the truck cannot move from the inspection site until the defect is corrected (vehicle OOS) or the driver is replaced (driver OOS). For carriers, every OOS violation adds time-weighted points to your CSA Vehicle Maintenance BASIC — and it shows in the public SMS data within 30 days. For drivers, an OOS event stays on PSP for 3 years.

CSA / SMS impact

393.79 carries a severity weight of 4/10 in FMCSA's Safety Measurement System (SMS). Higher weights mean faster CSA percentile movement. Combined with a time-weighting factor (2× for citations within the last 6 months, decaying over 24 months), this violation can move your Vehicle Maintenance BASIC percentile significantly if it stacks with similar citations across your fleet. The threshold for FMCSA intervention is the 65th percentile for most BASICs (50th for Hazmat and Passenger Carrier). Once you cross that, FMCSA can send a Warning Letter, Off-Site Investigation, or full Compliance Review.

How to read this: a single citation rarely puts you over threshold — it's the pattern. Track your inspection rate per power unit and aim for OOS rate under 5% (industry average is 21%).

Carriers recently cited (last 24 months)

Carriers most-recently cited for 393.79 in FMCSA inspection records (rolling 24-month window).

JESUS MA VALDEZ GARCIA
DOT #2534784 • last cited 2026-10-24
27×
FEDERAL EXPRESS CORPORATION
DOT #86876 • last cited 2026-10-23
24×
EBI TRANSFERS SA DE CV
DOT #3187987 • last cited 2026-10-23
24×
PEDRO ESPINO DIAZ
DOT #2937836 • last cited 2026-10-26
23×
JOSE ALFREDO JIMENEZ CAMACHO
DOT #3586792 • last cited 2026-08-14
22×
SERVICIOS ADUANALES RM S DE RL DE CV
DOT #3050679 • last cited 2026-10-09
19×
ARTEMIO VILLARREAL DEL BOSQUE
DOT #2055979 • last cited 2026-10-30
16×
ISABEL CRISTINA PEREZ GARCIA
DOT #4070075 • last cited 2026-11-04
15×
4G TRANSFER US-MEX SA DE CV
DOT #2828651 • last cited 2026-09-10
15×
MARTHA LIZETH ESPINO DIAZ
DOT #4143144 • last cited 2026-11-04
14×

Other violations in Vehicle Maintenance

396.9C2OOS

Operating vehicle declared out-of-service

393.75AOOS

Flat tire or audible air leak

393.75A1OOS

Tire ply or belt material exposed

393.75A3OOS

Tire with fabric exposed

393.75FOOS

Tire on steering axle under 4/32 inch tread

393.75GOOS

Tire on non-steering axle under 2/32 inch tread

393.83A2OOS

Exhaust discharges into cab/sleeper

393.5AOOS

Coupling device defective (fifth wheel, pintle, kingpin)

Frequently Asked Questions

Can I be placed out of service for 393.79?

Yes. 393.79 is on the North American Standard Out-of-Service Criteria list. An inspector who finds this during a Level 1, 2, or 3 inspection can place the Vehicle OOS at the inspection site. The truck cannot move until the defect is corrected. For vehicle-side OOS, that usually means a mobile mechanic or tow to the nearest shop. For driver-side OOS (HOS, CDL, drug/alcohol), it means the driver is removed from service and a qualified replacement must arrive before the truck can continue. Pro tip: do a thorough pre-trip every shift and address any issue listed in 49 CFR 393 before pulling onto the road — that's the only reliable way to avoid this one.

How long does 393.79 affect my CSA score?

393.79 stays in your CSA Vehicle Maintenance BASIC for 24 months from the inspection date. The impact is time-weighted: 3× points during months 0-6, 2× during months 7-12, 1× during months 13-24, then it drops off. Severity weight is 4/10, so each citation contributes 12 points in the first 6 months and decays from there. On the driver's PSP report, the same citation stays visible for 36 months — and a 5-year history of driver violations is available to motor carriers performing a hire review. If the citation is later dismissed in court (DataQs challenge succeeds, or the underlying ticket is dropped), the SMS record can be removed via FMCSA's DataQs portal — but you have to actively file the challenge.

What's the difference between 393.79 and similar codes?

393.79 is in the 8-code group sharing the same BASIC. The closest siblings are: 396.9C2 (Operating vehicle declared out-of-service); 393.75A (Flat tire or audible air leak); 393.75A1 (Tire ply or belt material exposed). Inspectors often cite multiple sibling codes from the same inspection — for example, a tire condition violation can simultaneously trigger codes for tread depth, sidewall, and inflation pressure. When you get cited under one sibling, check the report for the others before signing — they all count separately against CSA scoring.

How often is 393.79 cited?

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393.79 — Defroster/defogger inoperative

What this violation means

Related

Frequently Asked Questions

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