FMCSR 393.43D: Relay Emergency Valve Violations Explained

Yes, almost certainly. Even though 393.43D is technically not OOS-eligible on paper, our inspection records show that across 4,729 all-time citations, 4,415 vehicles were placed out of service—a 93.4% OOS rate. That is nearly three times the all-FMCSR average of 31.4%. In practice, inspectors are finding defective relay or emergency valves so severe that they trigger OOS action under companion brake defect criteria. If your vehicle is cited under 393.43D, assume you will not be driving it away from the inspection site without repairs.

A 393.43D citation carries a severity weight of 7 in the FMCSA Safety Measurement System. That score is then multiplied based on how recently the inspection occurred: violations in the last 6 months get a 3× time-weight multiplier, violations 7–12 months ago get 2×, and violations beyond 12 months get 1×. So a fresh 393.43D citation can contribute as many as 21 weighted points to your Vehicle Maintenance BASIC before percentile calculations are applied. With 3,011 citations logged in just the last 12 months, inspectors are actively looking for this defect.

Stop the vehicle and get the valve inspected and repaired before moving the truck under its own power. Here are the immediate steps:

1. Document everything — photograph the valve, the citation, and the inspection report.
2. Check for companion violations — our records show that in the last 90 days, 393.43D citations co-occurred with 396.17C (no periodic inspection proof) in 253 inspections and with 393.48A (inoperative brakes) in 115 inspections. Review your inspection paperwork closely.
3. Get a qualified mechanic to sign off on the repair — you'll need a repair receipt to clear the violation.
4. Notify your safety department — the citation hits both driver and carrier CSA scores.

Yes, it is among the most serious in its category by OOS rate. Our inspection records show 393.43D's 93.4% OOS rate dwarfs peer Vehicle Maintenance codes: 393.47E (slack adjuster defective) carries a 0.0% OOS rate across 180,363 citations, and 393.9(a) (inoperable required lamps) sits at 15.4% across 660,737 citations. Even 396.3(a)(1), a broad maintenance catch-all with 236,919 citations, has only a 45.3% OOS rate. A defective relay or emergency valve essentially guarantees enforcement action when found.

Yes, you can file a DataQs request for review (RDR) on any roadside inspection violation, including 393.43D. Because this is an equipment defect finding rather than a documentation issue, a successful challenge typically requires evidence that the violation was recorded in error—for example, inspection records showing the valve was tested and functional at the time, or proof of a mechanical misidentification. DataQs challenges on equipment citations are harder to win than paperwork disputes, but if the inspector made a factual error, submitting a repair order dated before the inspection or a certified mechanic's statement can support your case. The RDR is filed at the FMCSA DataQs portal and routed to the issuing state agency for review.

Texas, Iowa, and North Carolina are the top three enforcement states. In the last 180 days, our inspection records show Texas issued 861 citations with a 91.3% OOS rate, Iowa issued 253 citations with a 98.0% OOS rate, and North Carolina issued 64 citations—all 64 resulting in an OOS order, a 100.0% rate. Illinois and New Mexico also logged 100.0% OOS rates on their citations during the same period. If your routes pass through Texas, expect this to be an active enforcement target.

No. Repair urgency is immediate. Our database records 541 citations in just the last 90 days, and the monthly trend shows enforcement has been consistently high—328 citations in October 2025 alone, with 306 of those resulting in OOS orders. The 93.4% all-time OOS rate means that in nearly every case where this defect is found, the vehicle is grounded on the spot. Waiting until the next scheduled maintenance cycle is not a realistic option; the vehicle will be pulled from service by an inspector before that cycle arrives if the valve is found defective.

It follows both. Under FMCSA's CSA methodology, a roadside inspection violation is assigned to the carrier operating the vehicle at the time of the inspection and to the driver listed on the inspection report. The citation attaches to the carrier's Vehicle Maintenance BASIC percentile and simultaneously appears on the driver's inspection history, which carriers can view when making hiring decisions. With 4,729 all-time citations in our records, 393.43D is not an obscure code—safety managers screening driver histories will see it. Drivers who change carriers do not leave the citation behind.