FMCSR 393.43(b) — Brake Relay/Emergency Valve | Q&A

No. A 393.43(b) citation does not result in an out-of-service order. Across our inspection records, this code has been cited 280 times all-time with a 0.0% out-of-service rate—every single citation allowed the vehicle to remain in operation.

That said, the defect itself (a malfunctioning brake relay or emergency valve) is a safety issue that needs repair. The citation flags the problem; the repair timeline is your responsibility to manage with your carrier or maintenance team.

A single 393.43(b) citation carries a 7-point CSA severity weight. CSA points accumulate over a rolling 12-month period and roll off after that window closes. The 7-point value reflects the safety risk of a defective brake system component, even though this specific violation does not trigger an immediate out-of-service ruling.

Multiple citations within 12 months stack. If you're managing a fleet, track the cumulative weight to stay below intervention thresholds.

Immediate steps:

1. Do not ignore the citation. Even though it's not an OOS violation, it creates a CSA record.
2. Contact your carrier's maintenance department and provide the citation details—specify the relay or emergency valve location noted by the inspector.
3. Schedule repair immediately. While you can continue operating, the brake component is documented as defective. Delaying repair increases legal and insurance risk.
4. Request a repair receipt. Once fixed, keep proof of correction for your records and DataQs appeals (if you contest).
5. Review your pre-trip inspection routine to catch similar issues before roadside inspection.

In isolation, no—it has a 0.0% out-of-service rate versus the 31.4% average across all FMCSR codes. However, it sits in the same Vehicle Maintenance category as far more frequent violations. For example:

• 393.47E (slack adjuster defective): 180,363 citations, 0.0% OOS rate
• 393.9(a) (inoperable required lamps): 660,737 citations, 15.4% OOS rate

A relay/emergency valve defect is less commonly cited (280 all-time, ranked #1112 of 3,036 codes), but it directly affects brake safety. The low citation volume may mean inspectors catch it inconsistently—not that it's minor.

Yes, you can contest any roadside inspection citation through the DataQs/RDR (Roadside Data Review) process. You have 15 calendar days from the inspection date to file a challenge.

For 393.43(b), contestability depends on the evidence: if the inspector documented a defective relay or emergency valve without verifying operation or providing clear photos, you may have grounds to dispute. If a subsequent repair shop found the component functional, that documentation strengthens your case.

File through FMCSA's Safety Management System (SMS) portal or your carrier's compliance team. Disputes require supporting evidence (repair records, inspection photos, technician statements).

Very urgent from a safety and compliance standpoint. The 0.0% out-of-service rate does not mean the defect is minor—it means you're legally permitted to drive while it exists.

However, our inspection data shows zero citations in the last 12 months and zero in the last 90 days, suggesting this violation is rare. That rarity should not be mistaken for lenience. A malfunctioning brake relay or emergency valve compromises your entire brake system's redundancy.

Repair within 48–72 hours. The longer you delay, the higher the risk of brake failure on the road and the harder it becomes to argue good-faith compliance if cited again.

Across our 13 million+ inspection records, 393.43(b) citations concentrate in a small carrier base:

• Autotransportes Romedu SA de CV (USDOT 1148259): 12 citations
• Claudia Belinda Andarza Leal (USDOT 963435): 9 citations
• Transporte Internacional Lopez Ochoa SA de C V (USDOT 1041907): 6 citations

The pattern suggests these carriers operate older or less-maintained fleets, or operate routes where brake system inspection is more frequent. If you drive for one of these carriers, heightened attention to brake pre-trip inspection is warranted.

Across all-time citations, these makes dominate:

• Freightliner: 82 citations
• International: 77 citations
• Kenworth: 44 citations
• Great Dane: 29 citations

Freightliners and Internationals account for roughly 57% of all 393.43(b) citations. This may reflect their prevalence in long-haul fleets, but it also suggests these makes' brake systems (or their maintenance) receive inspector scrutiny more often. If you operate one of these tractors, budget preventive brake maintenance into your compliance calendar.