What 393.43A means in plain language
A relay or emergency valve on your commercial motor vehicle is not working correctly. These valves are critical safety components in your air brake system—they control how air pressure builds and releases to stop your truck safely.
When an inspector or safety officer finds that one of these valves is defective or malfunctioning, they cite you under 393.43A. This could mean the valve is leaking, not opening or closing properly, or not holding air pressure as designed. The problem may be visible during inspection, or discovered through functional testing of your brake system.
Unlike some brake violations, 393.43A does not automatically place your vehicle out of service on the citation itself. However, as our inspection records show, 79.8% of vehicles cited for this code are still removed from service—meaning inspectors often find the defect severe enough to ground the truck until it's repaired.
What our enforcement data actually shows
Across our 13 million roadside inspection records, we have documented 2,084 all-time citations for 393.43A, making it the #522 ranked code out of 3,036 FMCSR codes by citation volume. In the last 12 months, we recorded 1,355 citations, and in the last 90 days, 373 citations.
The out-of-service rate for 393.43A is 79.8%—significantly higher than the all-FMCSR average of 31.4%. This tells you that when inspectors cite this violation, they judge it serious enough to sideline vehicles nearly 80% of the time. Over the code's entire history in our database, 1,664 vehicles were placed out of service versus 420 that were not.
Monthly data shows enforcement has been increasing. March 2026 saw a spike to 191 citations with 112 out-of-service actions. The most recent full month (March 2026) reflects sustained enforcement pressure on brake-related defects.
Who gets cited most
Our enforcement data shows Texas leads by a large margin: 710 citations in the last 180 days, with a 56.9% out-of-service rate. New Mexico follows with 45 citations and a 100% out-of-service rate—every vehicle cited was grounded. Illinois, Iowa, and North Carolina complete the top five, each with smaller citation counts but notably high out-of-service rates (100%, 100%, and 85.7% respectively).
The variation in out-of-service rates across states is material. Texas's 56.9% rate is substantially lower than New Mexico's 100%, suggesting either different inspection standards, vehicle fleet composition, or repair infrastructure differences between states.
Regarding specific carriers, our data shows fleets such as TRAREYSA SA DE CV with 21 citations and QUALITY TANK SA DE CV with 17 citations have faced repeated enforcement. This pattern suggests that certain operations—particularly those in border and cross-border regions—encounter this citation more frequently.
How severe is this compared to similar codes
Within the Vehicle Maintenance category, 393.43A occupies a middle ground for severity. The inoperable required lamps code (393.9) has far more volume at 660,737 all-time citations but only a 15.4% out-of-service rate—suggesting brake defects are treated much more seriously than lighting issues. The slack adjuster defect code (393.47E) has 180,363 citations but a 0.0% out-of-service rate, indicating that code typically results in citations without immediate vehicle removal.
By contrast, the general inspection/repair/maintenance code (396.3(a)(1)) has 236,919 citations with a 45.3% out-of-service rate. The 393.43A out-of-service rate of 79.8% places it in the upper tier of enforcement severity for vehicle maintenance violations.
How to avoid it
Our inspection data reveals patterns in which violations co-occur with 393.43A. In the last 90 days, inoperable lamps (393.9) appeared in 133 shared inspections, and brake tubing/hose inadequacy (393.45B2UV) in 104 shared inspections. This tells us that brake system maintenance is the core issue. Here are concrete actions:
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Perform a full brake system walk-around before every trip. Listen for air leaks near the relay and emergency valve. Feel for moisture or oil seepage around valve connections. Do not start your day if you hear hissing or smell oil near the brake system.
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Test your air pressure build-up and hold. After engine start, watch your air gauge climb and hold steady. If pressure takes longer than normal to build or drops when the engine is off, your relay or emergency valve may be failing. Report this to your dispatcher and maintenance immediately.
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Inspect brake lines and fittings monthly. Corroded or loose fittings accelerate valve failure. Our data shows brake tubing issues co-occur with 393.43A defects in many inspections. Check all visible brake lines for cracks, loose connections, or corrosion, especially in salt-belt states.
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Keep your vehicle manufacturer's maintenance schedule. Freon and Kenworth vehicles account for the majority of citations in our database (612 and 522 respectively). These manufacturers publish specific brake system service intervals—follow them strictly and keep service records.
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If you notice any brake performance change—longer stopping distance, spongy pedal feel, or unusual sounds—do not continue driving. Have your relay and emergency valve inspected before the next trip. A preventive inspection costs far less than downtime from an out-of-service citation.