What 393.43(e) means in plain language
Your truck's air brake system relies on several valves to work correctly. The relay valve and emergency valve are critical components that control how air pressure moves through your brake lines. When either of these valves becomes defective or malfunctions, your brakes cannot function as designed—even if other brake components appear intact.
A relay valve speeds up the application of service brakes by reducing the distance air must travel through the system. An emergency valve provides a fail-safe that applies the parking brakes if air pressure drops unexpectedly. If an inspector finds evidence that either valve is not working properly—whether it's leaking, not opening or closing fully, or producing abnormal sounds—you'll be cited under 393.43(e).
This is fundamentally a pre-trip inspection failure. Drivers are expected to know their brake system well enough to detect symptoms like slow brake response, hissing sounds from the valve area, or warning light activation on the dashboard.
What our enforcement data actually shows
Across 13 million inspections in our database, 393.43(e) has generated 337 all-time citations. Notably, there have been zero citations in the last 12 months and zero in the last 90 days, indicating this violation is extremely uncommon in current roadside enforcement.
None of the 337 all-time citations resulted in an out-of-service order. The 0.0% out-of-service rate for 393.43(e) contrasts sharply with the 31.4% all-FMCSR average, meaning when inspectors find relay or emergency valve defects, they typically issue a citation but allow the vehicle to continue under specific conditions (such as immediate repair or limited operation). This code ranks #1050 out of 3,036 FMCSR codes by citation volume, placing it in the lower tier of enforcement activity.
The absence of recent citations suggests either improved brake system maintenance across the industry or a shift in inspection focus toward other brake-related codes.
Who gets cited most
Our inspection records do not include state-level breakdowns for this particular code in our current dataset. However, our data shows that carriers operating in cross-border and international freight corridors have historically received citations under 393.43(e). For example, TRANSPORTES TERRESTRES VALDEZ SA DE CV (USDOT 2473066) and CASA TRUCKING LLC (USDOT 603725) each accumulated 5 citations all-time, the highest counts in our records. These numbers reflect the scale of operations and inspection exposure rather than systemic deficiency.
The prevalence of international-operation carriers in the top-cited group suggests that relay and emergency valve defects may correlate with older equipment or higher utilization rates typical of long-haul and cross-border fleets.
How severe is this compared to similar codes
When we compare 393.43(e) to other vehicle maintenance citations in the same regulatory category, the enforcement pattern is notable. For instance:
- 393.9(a) — Inoperable required lamps has been cited 660,737 times with a 15.4% out-of-service rate. Lamp defects are far more frequently cited but less likely to trigger immediate removal.
- 396.3(a)(1) — Inspection/repair/maintenance (general) shows 236,919 citations with a 45.3% out-of-service rate, indicating that broad maintenance violations are both more common and more likely to be deemed safety-critical.
- 393.47E — Slack adjuster defective (another brake component) has 180,363 citations with a 0.0% out-of-service rate, similar to 393.43(e) in outcome but vastly higher in enforcement volume.
The scarcity of 393.43(e) citations relative to other brake codes suggests that relay and emergency valve defects are either caught during routine maintenance before roadside inspection, or that inspectors prioritize more frequent violations in the brake system category.
How to avoid it
Prevent 393.43(e) citations by integrating these checks into your pre-trip inspection routine:
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Listen for air brake sounds during application. As you apply the brakes gently in a safe area, the relay valve should respond smoothly without hissing, chattering, or delayed engagement. Any unusual sound near the valve location warrants immediate inspection by a certified technician.
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Check brake response consistency. If you notice that brakes feel soft, sluggish, or require longer stopping distances than usual, the relay valve may not be functioning. Do not drive—have your mechanic test valve operation before returning to service.
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Inspect for visible leaks or damage around valve assemblies. During your walk-around, look for wet spots, corrosion, or broken fittings on the relay and emergency valve housings. Even small leaks indicate internal defects.
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Verify dashboard warning lights during startup. Modern trucks display air pressure and brake system warnings. If warning lights remain illuminated after engine start, air may be leaking from the emergency valve circuit. Address this before operating.
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Know your truck's year and model. Freightliners and Utility trailers (the most-cited makes in our data with 124 and 77 citations respectively) should receive extra scrutiny if they are older units, as valve seals degrade over time.
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Request annual brake system certification. Many repair shops include relay and emergency valve testing as part of comprehensive air brake service. Schedule this annually or after 100,000 miles, whichever comes first.
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Report any symptoms immediately to your dispatcher or safety manager. If you suspect a brake valve issue, document the behavior, stop operation, and coordinate repairs. Early detection prevents citations and keeps you safe.