FMCSR 393.43(d) Relay Emergency Valve: Driver Q&A

Almost certainly — our inspection records show a 96.7% out-of-service rate across all 13,151 citations for this code. That means 12,720 out of 13,151 vehicles cited under 393.43(d) were placed out of service on the spot. For context, the all-FMCSR average OOS rate is only 31.4%, so this violation runs more than three times hotter than the typical FMCSR code. Even though the code is technically flagged "OOS eligible: no" at the regulatory level, inspectors on the ground have consistently pulled trucks for it. Do not assume you'll drive away.

393.43(d) carries a severity weight of 7 on the FMCSA CSA scale. That 7-point base is then multiplied by a time-weight factor depending on how recently the inspection occurred: violations within the last 6 months receive the highest multiplier (3×), dropping to 2× for months 7–12 and 1× for months 13–24. So a fresh citation translates to 21 weighted points before any additional multipliers for crashes or prior history. This feeds into the Vehicle Maintenance BASIC, which is one of the most scrutinized categories during carrier interventions.

Take these steps immediately:

1. Do not move the vehicle until the relay or emergency valve is inspected and, if confirmed defective, repaired by a qualified mechanic — 96.7% of vehicles cited for this violation were placed out of service.
2. Get the inspection report (the MCS-63 or equivalent roadside form) and photograph the valve and surrounding components before any repairs.
3. Notify your fleet safety manager or dispatcher so the repair is documented in your maintenance file — this matters if you contest the citation later.
4. Retain all repair invoices and parts records with timestamps; you'll need them for a DataQs challenge or a compliance review.
5. Confirm the fix with a qualified inspector before re-entering service.

Yes — it is dramatically more serious than most violations in the same category. Our inspection records show a 96.7% OOS rate for 393.43(d), compared to just 15.4% for 393.9(a) (inoperable required lamps) and 45.3% for 396.3(a)(1) (general inspection/repair/maintenance). Even the all-FMCSR average sits at only 31.4%. Nationally, 393.43(d) ranks #186 out of 3,036 FMCSR codes by citation volume, so inspectors know it well. The combination of a 7-point CSA severity weight and a near-universal out-of-service outcome makes this one of the highest-consequence brake-system codes in active enforcement.

Yes, you can submit a Request for Data Review (RDR) through FMCSA's DataQs system for any roadside inspection finding, including 393.43(d). Because this is an equipment violation — not a documentation issue — a successful challenge typically requires hard evidence: repair invoices showing the valve was replaced or certified functional, a mechanic's signed statement, or parts records with timestamps predating the inspection. DataQs challenges on equipment findings are harder to win than paperwork disputes, but they are worth pursuing if you have documentation proving the citation was issued in error. The record stays on your SMS profile for 24 months if unchallenged.

Across our database of 13,151 all-time citations for 393.43(d), the top vehicle makes cited are Ford (3,174 citations), followed by Dodge (1,384) and Chevrolet (911) — pointing to a heavy concentration in light-to-medium commercial units rather than traditional heavy trucks. The statistics block for this code does not break citations down by state, so we cannot name specific states without inventing figures. What the data does confirm is that the violation spans a wide range of carrier types, from equipment rental firms to landscaping fleets, suggesting enforcement is geographically broad rather than concentrated in a single corridor.

It cannot wait. The 96.7% out-of-service rate across 13,151 citations means inspectors treat a defective relay or emergency valve as an immediate safety threat in virtually every encounter. Driving with a known defect after a citation exposes you to a second, compounding violation and additional CSA points on top of the original 7-point severity weight. While enforcement volume shows 0 citations in the last 90 days and 0 in the last 12 months in our current records — suggesting the code may have been reclassified or folded into other brake codes — any active defect in this system should be corrected before the vehicle moves.

It follows both, but in different BASIC categories. Under FMCSA's CSA methodology, a roadside equipment violation like 393.43(d) is assigned primarily to the carrier's Vehicle Maintenance BASIC, since the carrier is responsible for keeping the vehicle in safe operating condition. The driver's record is also linked to the inspection event and appears in their PSP (Pre-Employment Screening Program) report for prospective employers. Carriers with repeated citations in this code — such as LBS Logistics Inc. with 23 all-time citations — accumulate Vehicle Maintenance BASIC percentile pressure that can trigger FMCSA interventions.