FMCSR 393.43 Relay Emergency Valve: Driver Q&A

Yes — and the odds are extremely high. Across 23,816 all-time citations in our inspection records, 393.43 carries an 81.7% out-of-service rate, meaning 19,467 of those stops ended with the vehicle parked on the spot. That is more than 2.5 times the all-FMCSR average OOS rate of 31.4%. A defective or malfunctioning relay or emergency valve is treated as an immediate safety threat by inspectors, not a paperwork issue. Plan on the truck not moving until the component is repaired and the inspector clears it.

393.43 carries a severity weight of 7 in the FMCSA SMS system. That is on the higher end of the Vehicle Maintenance BASIC scoring range. The actual points that hit your record are multiplied based on how recently the inspection occurred — violations within 6 months receive the heaviest multiplier, those between 6 and 12 months receive a reduced multiplier, and anything older than 12 months carries the lowest weight. Because the violation also triggers an OOS finding 81.7% of the time, expect the OOS designation itself to further elevate your Unsafe Driving and Vehicle Maintenance BASIC scores.

Stop operating and get the valve repaired before the truck moves. Here is a practical sequence:

1. Document everything — photograph the valve, air lines, and any visible defect before the repair shop touches it.
2. Get a certified repair — you will need a signed repair receipt to clear the OOS order.
3. Check surrounding systems — our inspection records show that in the last 90 days, 393.43 citations frequently appeared alongside 393.9 (inoperable lamps, 110 shared inspections), 396.17C (no proof of periodic inspection, 106 shared inspections), and 393.95A (missing or defective fire extinguisher, 95 shared inspections). Inspectors who find this violation tend to write up multiple items.
4. Notify your fleet safety manager immediately so the driver qualification file and maintenance records are current before any follow-up inspection.

Yes — it stands out sharply even among brake-related violations. Our inspection records rank 393.43 at #114 out of 3,036 FMCSR codes by total citation volume, which is notable for a specific component-level rule. More telling is the OOS rate: 81.7% versus a 31.4% all-FMCSR average. For context, peer Vehicle Maintenance codes like 393.9(a) (inoperable lamps) have a 15.4% OOS rate and 396.3(a)(1) (general inspection and maintenance) sits at 45.3%. No other commonly cited maintenance code in our database comes close to 393.43's OOS rate. Inspectors treat a faulty relay or emergency valve as a brake system integrity failure, not a minor defect.

It depends on the basis of your challenge. The FMCSA DataQs system (Request for Data Review) lets carriers and drivers dispute inspection findings they believe are inaccurate. Because 393.43 is an equipment-condition violation — not a documentation issue — a successful challenge typically requires evidence that the valve was functioning properly at the time of inspection: repair records predating the stop, manufacturer specs showing the component met requirements, or a certified technician's written assessment contradicting the inspector's finding. Documentation-only violations like missing inspection stickers are generally easier to reverse. An equipment finding at an 81.7% OOS rate signals that inspectors are confident when they write this code, so your evidence needs to be specific and contemporaneous.

Texas, North Carolina, and Illinois lead all states in recent 393.43 enforcement. In the last 180 days, our inspection records show Texas issued 288 citations (70.1% OOS rate), North Carolina issued 258 citations (100.0% OOS rate), and Illinois issued 147 citations (99.3% OOS rate). New Mexico added another 61 citations, all resulting in an OOS finding (100.0% rate). If your routes pass through any of these states, relay and emergency valve condition should be a pre-trip checklist priority, not an afterthought.

No — at an 81.7% OOS rate, the answer is almost always that the truck stops where it is. Our inspection records show 356 citations in just the last 90 days, and the monthly trend has stayed consistently high: May 2025 alone produced 193 citations with 165 resulting in OOS orders. Enforcement is active and year-round. Driving to a shop on a known relay or emergency valve defect risks a second, more serious citation for operating under an OOS order — which carries its own severe CSA consequences. Contact a mobile brake technician or arrange a flatbed if necessary.

Both the driver and the carrier are affected. Under FMCSA's CSA methodology, Vehicle Maintenance BASIC violations like 393.43 are attributed to the carrier's SMS profile because the carrier is responsible for keeping the vehicle roadworthy. However, the inspection also appears on the driver's individual inspection history, which future employers can view through the Pre-Employment Screening Program (PSP). The severity weight of 7 means this citation has real staying power in both profiles. Carriers accumulate the BASIC percentile impact; drivers carry the inspection record — so both parties have direct incentive to prevent this violation through thorough pre-trip inspections.