FMCSR 393.43A — Brake Relay/Emergency Valve — Q&A

Yes, very likely. Across our 13 million inspection records, 393.43A results in an out-of-service placement 79.8% of the time—far above the 31.4% average for all FMCSR violations. Over the last 90 days, 373 citations were issued, with 297 resulting in immediate OOS orders. If you've been cited, expect your truck to be taken out of service until the relay or emergency valve is repaired and re-inspected.

A single 393.43A citation carries a severity weight of 7 points in the CSA system. Under the standard 30-day inspection window, this violation can accumulate up to 7 points toward your driver record. The exact CSA point multiplier depends on when violations occur within the 30-day cycle; multiple citations in the same period compound the impact. Check your FMCSA Safety Profile to see real-time accumulation.

First, do not operate the vehicle. Get the brake relay or emergency valve inspected and repaired by a certified technician immediately. Our data shows 393.43A frequently co-occurs with brake tubing/hose issues (393.45B2UV—104 shared inspections in the last 90 days) and slack adjuster defects (393.47E—66 shared inspections). Have the mechanic perform a full brake system audit, not just the valve. Once repaired, request a roadside re-inspection to clear the OOS order before attempting to move the truck.

Yes. The 79.8% OOS rate for 393.43A is dramatically higher than peer codes in vehicle maintenance. For comparison, the inoperable lamp code (393.9) has a 6.9% OOS rate, slack adjuster defects (393.47E) trigger 0.0% OOS placement, and general inspection/repair issues (396.3A1) result in 45.3% OOS. A defective relay or emergency valve is a critical brake component failure—inspectors treat it as a safety showstopper, not a minor defect.

Over the last 180 days, Texas dominates enforcement with 710 citations and a 56.9% OOS rate. New Mexico follows with 45 citations (100% OOS rate), and Illinois with 11 citations (100% OOS rate). Texas accounts for the vast majority of 393.43A activity across the nation. If you operate in Texas, prioritize brake system inspections as part of your preventive maintenance routine.

Enforcement is spiking. In March 2026, 191 citations were issued—the highest month in the last 12 months. February 2026 saw 136 citations, January 145, and December 154. Compare this to April 2025 (25 citations) and you see a clear upward trend. The 90-day rolling average stands at 373 citations, signaling increased roadside inspector focus on brake relay and emergency valve defects. Repair and compliance urgency is high.

Yes, if the defect finding is inaccurate or based on inspection error, you may file a DataQs challenge with FMCSA. However, contestation is difficult when the valve is demonstrably defective. DataQs is most effective for documentation disputes—e.g., if you repaired the valve before the inspection but the report is wrong. Physical equipment failures are harder to overturn. File within 90 days of the citation; include repair records, photos, or re-inspection results proving the component was already fixed. Consult your safety manager or attorney for strategy.

Our inspection data shows Freightliner (612 citations all-time) and Kenworth (522 citations) account for the majority of 393.43A violations. This reflects their prevalence in the trucking fleet, not a design defect. These makes are cited proportionally more often because they represent a larger share of registered commercial vehicles. Regardless of truck make, relay and emergency valve maintenance should follow manufacturer specifications and be logged during pre-trip and post-trip inspections to catch early failure signs.