What 393.42(a) means in plain language
Your parking brake system must be capable of holding your commercial motor vehicle stationary on its own. When an inspector cites you for 393.42(a), they've determined that your parking brake — whether hydraulic, air, or mechanical — cannot reliably do that job.
This isn't about your service brakes (the ones you use while driving). This is specifically about the brake you engage when the truck is parked or stopped for an extended period. If an inspector can move your vehicle or detect excessive brake lever travel, or if the brake doesn't engage with reasonable force, you're at risk for this citation.
The parking brake is a safety device. A defective one means your vehicle could roll unattended, endangering property, cargo, and people. That's why inspectors take it seriously.
What our enforcement data actually shows
Across our 13 million+ inspection records, 393.42(a) has generated 652 citations all-time, placing it at rank #836 out of 3,036 FMCSR codes by citation volume. In the last 90 days and last 12 months, we recorded zero citations for this code, indicating either excellent recent compliance or a shift in inspector focus.
When a 393.42(a) citation is issued, there's a 30.1% chance the vehicle is placed out-of-service. This is slightly lower than the all-FMCSR average out-of-service rate of 31.4%, meaning parking brake defects are somewhat less likely to trigger an immediate roadside shutdown than violations across all maintenance codes. However, nearly 1 in 3 vehicles cited still cannot continue their route — a significant enforcement consequence.
Of the 652 all-time citations, 196 resulted in out-of-service orders and 456 did not. This split shows that some brake defects are minor enough to allow continued operation after repair, while others are severe enough to ground the vehicle on the spot.
Who gets cited most
Our inspection records do not include a state-level breakdown for this specific code in the data provided. However, our top carriers cited for 393.42(a) show a pattern across smaller and mid-sized fleets. Boat Magazine Inc, Two Brothers Transports LLC, Nelson Sanitation & Rental Inc, and Bennett Truck Transport LLC each received 6 citations all-time. This suggests that parking brake defects are not confined to any single carrier type or size — they occur across diverse operations.
The vehicle makes most frequently cited for this violation include Ford (111 citations), Dodge (39 citations), and Freightliner (34 citations). Ford vehicles account for a notable portion of all 393.42(a) citations, though this reflects both market prevalence and the age of many Ford units still in service. Kenworth and International trucks also appear in the top 10, indicating that parking brake issues affect both light- and heavy-duty equipment.
How severe is this compared to similar codes
Parking brake defects are far less common than other brake-related violations. The peer code 393.9(a) — Inoperable Required Lamps — has been cited 660,737 times with a 15.4% out-of-service rate, making it over 1,000 times more frequent than 393.42(a). Another peer code, 396.3(a)(1) — Inspection/Repair/Maintenance General — shows 236,919 citations with a 45.3% out-of-service rate, meaning that general maintenance violations more than double the out-of-service frequency.
By contrast, 393.47E (Slack Adjuster Defective) has been cited 180,363 times but carries a 0.0% out-of-service rate. This code relates to service brake adjustment, not parking brake function. The rarity of 393.42(a) citations — just 652 all-time — suggests that most fleets maintain parking brakes adequately, or inspectors cite them infrequently relative to other defects.
How to avoid it
Parking brake maintenance is straightforward if you establish a pre-trip routine:
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Test your parking brake before every departure. With the engine running and the truck on level ground, apply the parking brake fully and try to move forward gently in a low gear. Resistance should be immediate. If the truck creeps forward or the brake requires excessive force, have a mechanic inspect it before driving.
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Inspect the brake lever or pedal for excessive travel. When you engage your parking brake, it should lock firmly within 2–3 inches of lever travel (or the equivalent for foot-operated systems). If it sinks or requires more travel than usual, the system may be losing pressure or developing slack.
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Check for air or hydraulic leaks in the parking brake circuit. A hissing sound when the brake is engaged, or fluid pooling under the truck, means the system cannot hold pressure. Do not drive; arrange for repairs immediately.
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Pay special attention if you operate Ford, Dodge, or Freightliner units. Our data shows these makes account for a large share of parking brake citations. If you maintain one of these vehicles, add a dedicated parking brake check to your weekly pre-trip inspection, not just daily.
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Do not ignore sluggish engagement. If your parking brake requires more force than usual to engage, or if you notice it slipping over a few weeks, have the adjustment checked. A mechanic can tighten slack adjusters or bleed air from hydraulic systems before a roadside failure occurs.
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If you receive a citation for 393.42(a), repair it immediately. With a 30.1% out-of-service rate, the next citation for the same defect will likely ground your truck. Schedule repairs as soon as you can reach a service facility.
The parking brake is one of the simplest systems to verify before you roll. Five minutes of testing can prevent a citation, a fine, and downtime.