What 393.41 means in plain language
FMCSR 393.41 requires that every commercial motor vehicle be equipped with a parking brake system that is functional and adequate to hold the vehicle stationary. If an inspector finds that your parking brake is either completely absent or in a condition where it cannot perform its intended job, you are in violation of this regulation.
The rule applies broadly across CMV types — it is not limited to tractor-trailers or heavy combination vehicles. If the parking brake mechanism is worn, disconnected, leaking air, or otherwise unable to keep the vehicle from rolling when applied, that is a defective condition under this code.
In practical terms, when an officer pulls you in for inspection and tests your parking brake — either by applying it and checking for hold or by physically examining the components — any failure to demonstrate a working system puts you at immediate risk of being placed out of service on the spot.
What our enforcement data actually shows
This is one of the most consequential vehicle maintenance codes in the FMCSR system when you look at the numbers. Across our inspection database, 393.41 carries a 94.7% out-of-service rate — meaning that out of 11,285 all-time citations, 10,689 resulted in the driver being placed out of service and the vehicle being sidelined. To put that in perspective, the all-FMCSR average OOS rate across all codes is 31.4%. A 94.7% rate is nearly three times that baseline, making 393.41 one of the most reliably OOS-generating codes an inspector can write.
The code ranks #212 out of 3,036 FMCSR codes by total citation volume, which tells you inspectors encounter this problem regularly — it is not a niche or rarely-enforced rule. Over the last 12 months, our records show 799 citations issued under 393.41. In just the last 90 days, 137 citations were recorded, indicating this is an active and consistent area of enforcement, not a fading priority.
Looking at the monthly trend, citation volume has been climbing. The data in our database shows a jump from 35 citations in April 2025 to a peak of 92 in July 2025, with enforcement remaining elevated through the winter months — 59 citations in January 2026 and 61 in February 2026. This is not a seasonal spike that fades; inspectors are writing this violation year-round.
Who gets cited most
Over the last 180 days, Texas leads all states with 178 citations under 393.41, and 170 of those resulted in an OOS determination — a 95.5% rate. Iowa recorded 62 citations with a 93.5% OOS rate, while Illinois came in third with 40 citations and a striking 97.5% OOS rate. That 4-point gap between Iowa and Illinois is worth noting — Illinois inspectors are placing virtually every driver they cite under this code out of service. North Carolina and New Mexico round out the top five, with New Mexico recording a 100.0% OOS rate across its 9 citations in that window.
Our data shows that fleets such as Federal Express Corporation (USDOT 86876) with 98 all-time citations and United Parcel Service Inc (USDOT 21800) with 35 citations appear at the top of the carrier list. These are large operations with enormous fleets, so raw citation counts reflect scale as much as anything else. What the numbers do confirm is that no fleet type — from national parcel carriers to regional operators — is immune from this violation.
On the vehicle side, Ford leads all makes with 2,407 all-time citations under this code, followed by Dodge/DODG with 559 and Chevrolet/CHEV with 515. RAM and GMC round out the top five. The prevalence of light and medium-duty vehicle makes in this list is a signal that 393.41 is not just a heavy-truck issue — straight trucks, service vehicles, and smaller CMVs are regularly cited.
How severe is this compared to similar codes
Within the Vehicle Maintenance category, 393.41's 94.7% OOS rate stands apart from most of its peers. Consider 393.9(a), covering inoperable required lamps, which has 660,737 citations — far more volume — but only a 15.4% OOS rate. Drivers cited for a bad lamp are far less likely to be sidelined than drivers cited for a parking brake failure. The math is stark: a parking brake defect is roughly six times more likely to put you out of service than a lamp violation.
Look at 396.3(a)(1), the general inspection, repair, and maintenance code, which carries 236,919 citations and a 45.3% OOS rate. That rate is already above the 31.4% all-FMCSR average, and 393.41 still more than doubles it. Even codes directly tied to brake hardware, like 393.47E covering slack adjuster defects with 180,363 citations, carry a 0.0% OOS rate in our database — a sharp contrast to the near-universal OOS outcome that a parking brake deficiency produces. The enforcement community clearly treats the parking brake as a safety-critical system with very little tolerance for defects.
How to avoid it
The pattern of co-occurring violations in our 90-day data points directly to what inspectors are finding on the same vehicles where parking brakes fail. Use these as your pre-trip checklist anchors:
- Test the parking brake during every pre-trip — actively, not passively. Apply the brake fully, place the transmission in gear or release the service brake, and confirm the vehicle does not move. A visual check alone is not enough.
- Inspect brake system components for air leaks, worn chambers, and disconnected linkages. Code 396.3A1BOS — brakes out of service — appeared in 24 shared inspections with 393.41 in the last 90 days. A vehicle losing air elsewhere in the brake circuit often shows parking brake weakness too.
- Check relay and emergency valves. Code 393.43D, covering relay emergency valves, co-occurred in 24 inspections alongside 393.41. If your vehicle uses air-actuated parking brakes, the valve condition is directly tied to parking brake hold pressure.
- Don't skip lamp and safety equipment checks. Code 393.9 for inoperable required lamps appeared in 51 shared inspections — the most of any co-occurring code. Inspectors who find a lighting issue keep looking, and if your parking brake is also deficient, both violations land on the same report.
- Carry and inspect emergency equipment. Codes 393.95A and 393.95F — fire extinguisher and stopped-vehicle warning devices — appeared in 47 and 30 shared inspections respectively. A vehicle that lacks emergency gear is one that has often deferred maintenance broadly, including on the brake system.
- Ford, Dodge, and Chevrolet platform operators: pay extra attention. These three makes account for the largest share of 393.41 citations in our database. Parking brake cables and mechanisms on these vehicles are known to corrode or seize, especially in northern states. Lubricate and exercise the parking brake regularly, not just at inspection time.
- Verify your inspection documentation is current. Code 396.17C, no proof of periodic inspection, appeared in 42 shared inspections. A missing inspection record signals to the officer that maintenance discipline may be lacking — and that invites a closer look at everything, including the parking brake.