What 393.47A-BCFSBD means in plain language
This violation is written when an inspector finds that a brake chamber on your commercial motor vehicle has a housing that is cracked or broken. The brake chamber is the component that converts air pressure into the mechanical force needed to apply your brakes — so any structural failure of that housing is treated as a serious safety concern.
It does not matter whether the crack is hairline or fully shattered. If the inspector can identify a break or crack in the chamber body, the violation gets written. The regulation covers any CMV, which means tractors, straight trucks, trailers, and combination vehicles are all in scope.
This is not a paperwork issue or a minor administrative infraction. It sits inside the Vehicle Maintenance category of the CSA Safety Measurement System, and a citation here carries a severity weight of 8 — one of the heavier weights in the system — meaning it will affect how your carrier's BASIC scores are calculated for up to 24 months.
What our enforcement data actually shows
Across our 13 million+ inspection records, 393.47A-BCFSBD has been cited 5,720 times in total, ranking it #318 out of 3,036 FMCSR codes by citation volume. That puts it firmly in the upper tier of enforcement activity — most codes never reach that level of real-world citation frequency.
The pace of enforcement is accelerating. Our inspection records show 3,664 citations in the last 12 months alone, and 657 citations in just the last 90 days. Month-by-month, the data in our database indicates a peak of 450 citations in a single month (August 2025), and citation counts have remained elevated, with 319 citations recorded in March 2026.
One important piece of context: this code is not OOS-eligible by classification, yet our records show 360 out-of-service placements out of 5,720 total citations — a 6.3% OOS rate. That is well below the all-FMCSR average OOS rate of 31.4%, which reflects the non-OOS-eligible status of this code. However, a 6.3% rate still means that in more than 1 in 16 inspections where this violation was written, the vehicle was placed out of service anyway — almost certainly because of a companion violation found during the same inspection. That matters. Getting cited for 393.47A-BCFSBD does not automatically end your trip, but it raises the odds that an inspector will dig deeper.
Who gets cited most
Looking at the last 180 days, California leads all states with 298 citations and a 26.2% OOS rate for this code. Missouri is second with 105 citations and a 0.0% OOS rate. Tennessee comes in third with 74 citations, also at 0.0% OOS. The gap between California's 26.2% OOS rate and Missouri's 0.0% is material — more than 26 percentage points — and likely reflects California inspectors more frequently finding additional violations in the same inspection that trigger an OOS order. Kentucky, with 58 citations and a 25.9% OOS rate, follows a similar pattern to California.
Among carriers in our all-time data, fleets such as Evans Delivery Company Inc (USDOT 38111) with 18 citations and Servicio Internacional de Enlace Terrestre SA de CV (USDOT 818175) with 14 citations appear at the top of the citation list. The presence of multiple Mexico-domiciled carriers in the top ten is worth noting for fleets operating cross-border routes.
On the equipment side, Freightliner vehicles account for 1,245 all-time citations — the highest of any make in our database for this code — followed by FRHT at 735 and Kenworth at 458. If your fleet runs heavily Freightliner or Kenworth iron, brake chamber inspections should be a standing item in your maintenance program.
How severe is this compared to similar codes
Within the Vehicle Maintenance category, our inspection records show some stark contrasts. The peer code 393.9(a) — inoperable required lamps — has been cited 660,737 times, more than 115 times the volume of 393.47A-BCFSBD, but at a 15.4% OOS rate. The peer code 396.3(a)(1) — inspection, repair, and maintenance general — carries 236,919 citations and a 45.3% OOS rate, the highest among the peer group. Meanwhile, 393.47E — slack adjuster defective — sits at 180,363 citations with a 0.0% OOS rate.
What this comparison tells you: 393.47A-BCFSBD is a mid-volume code with a CSA severity weight of 8. That weight is higher than many of the high-volume lighting codes, which means each citation hits your carrier's Vehicle Maintenance BASIC harder per event. Do not treat a low citation count as a signal that inspectors overlook it.
How to avoid it
The co-occurring violation pattern in our data is a direct roadmap for pre-trip inspection priorities. In the last 90 days, 393.47A-BCFSBD appeared alongside 396.3A1-BOS (brakes out of service — 20% or more defective) in 254 shared inspections, and alongside 393.47E (slack adjuster defective) in 169 shared inspections. That tells you brake system problems cluster together. A cracked chamber rarely exists alone.
- Physically inspect every visible brake chamber housing before departure. Run your hand around the circumference of each chamber. Look for cracks along the seam, near the clamp band, or at the port connections. Do not rely on a visual scan from standing distance — cracks in cast metal are easy to miss.
- Check slack adjusters at the same time. Our data shows 393.47E co-occurred with this violation 169 times in 90 days. If the chamber is damaged, the adjuster may have been subjected to unusual stress. Check for proper travel.
- Listen for audible air leaks from each chamber. Our records show 396.3A1-BALAC (audible air leak from a brake chamber) appeared in 65 shared inspections. A cracked housing can leak before it fully fails. Build a full air pressure check into your pre-trip.
- Inspect brake tubing and hoses adjacent to each chamber. 393.45D-B and 393.45B2-B-AIR together appeared in 165 shared inspections alongside this code in 90 days. Damaged hoses and cracked chambers often share the same root cause — road impact or corrosion.
- Flag Freightliner and Kenworth vehicles for heightened attention. Our data shows these two makes together account for 1,980 all-time citations under this code. If your pre-trip checklist is generic, tighten the brake chamber inspection step specifically for those platforms.
- Do not drive away with a visibly compromised chamber. Even though this code is not OOS-eligible on its own, our data shows a 6.3% OOS rate in practice. The companion violations that get you parked are often found because the inspector started looking after writing this one.