What 393.45D means in plain language
FMCSR 393.45D targets the physical condition of the brake tubing and hoses on your commercial motor vehicle. Specifically, it covers situations where that tubing or hose shows visible damage — think worn-through outer jackets, sections that have been rubbed raw against a frame rail, hoses that have been pinched or kinked into a restricted shape, or any other deterioration that compromises the line's integrity.
The regulation doesn't require that your brakes have already failed. An inspector only needs to observe the damage itself — worn, chafed, crimped, or otherwise compromised tubing — and the citation is written. The condition of the line is the violation, not the downstream braking outcome.
For drivers, that means something you might mentally file under "I'll get that fixed at the next PM" can become a roadside citation before you ever reach the shop. Brake hoses and tubing run through tight, exposed areas of the chassis and are vulnerable to contact with moving parts, road debris, and heat — none of which wait for your next scheduled maintenance stop.
What our enforcement data actually shows
Across our 13 million+ inspection records, 393.45D has generated 3,113 all-time citations, placing it at rank #431 out of 3,036 FMCSR codes by citation volume. That puts it solidly in the upper tier of enforcement activity — not the most-cited code on the books, but far from obscure.
The pace of enforcement is accelerating. Our inspection records show 1,368 citations in the last 12 months and 248 citations in the last 90 days alone, indicating this is not a fading enforcement priority.
On out-of-service outcomes, 393.45D carries a 21.7% all-time OOS rate — 676 vehicles placed out of service out of 3,113 total citations. For context, the all-FMCSR average OOS rate across every code in our database is 31.4%, so 393.45D runs about 10 percentage points below that average. The code is not OOS-eligible as a standalone violation under standard criteria, yet 21.7% of cited vehicles still ended up out of service, which almost certainly reflects inspectors finding additional defects during the same inspection that pushed the vehicle over the OOS threshold.
Looking at the monthly trend, citation volume has been consistently elevated. Our data shows 197 citations in May 2025 — the highest single month in the trailing 12-month window — with counts ranging from 62 to 128 in most other months. The OOS companion count has also remained meaningful, hitting 39 in May 2025 and 35 in August 2025, reinforcing the point that brake hose defects rarely travel alone on a vehicle with deferred maintenance.
Who gets cited most
In the last 180 days, Iowa leads all states with 184 citations for 393.45D, followed by New Mexico at 173 citations and Illinois at 131 citations. The OOS rate variation across those three states is striking and worth understanding.
Iowa's OOS rate sits at 13.6% for this code. New Mexico's is 34.1% — more than 20 percentage points higher. Illinois comes in at 14.5%. North Carolina, with 86 citations, shows the highest OOS rate in the top-state group at 44.2%. Whether these gaps reflect inspector training differences, fleet-mix differences, or the tendency for brake hose violations to cluster with other defects in certain operational corridors, the data in our database indicates that the same citation can carry very different consequences depending on where you're inspected.
On the carrier side, our data shows fleets such as UNITED PARCEL SERVICE INC (USDOT 21800) with 12 all-time citations and SWIFT TRANSPORTATION CO OF ARIZONA LLC (USDOT 54283) with 11 all-time citations appearing at the top of the citation count list. Both operate at massive scale, and their appearance here reflects volume exposure more than anything else.
How severe is this compared to similar codes
Putting 393.45D in context with peer codes in the Vehicle Maintenance category clarifies where it sits on the severity spectrum.
Consider 393.9(a) — Inoperable Required Lamps — which has accumulated 660,737 citations in our database with a 15.4% OOS rate. That code is cited roughly 212 times more often than 393.45D, but carries a lower OOS rate. Brake hose violations are far less common but more likely to contribute to an OOS outcome when they appear.
Then look at 396.3(a)(1) — Inspection, Repair, and Maintenance (general) — which shows 236,919 citations and a 45.3% OOS rate. That code's OOS rate is more than double 393.45D's, but the two codes frequently appear together in the same inspection: our 90-day co-occurrence data shows 396.3A1 and 393.45D appearing on the same inspection report 30 times in just that window.
Finally, 393.47E — Slack Adjuster Defective — shows 180,363 citations at a 0.0% OOS rate as a standalone code, yet it co-occurred with 393.45D 27 times in the last 90 days. Brake system defects cluster. When an inspector finds one, the inspection tends to go deeper.
How to avoid it
The co-occurrence pattern in our inspection data tells a clear story: 393.45D rarely shows up in isolation. It appears alongside lighting defects, missing emergency equipment, general maintenance failures, and other brake-system codes. That means a pre-trip focused specifically on hose and tubing condition — combined with a broader brake system check — is your primary prevention tool.
- Trace every brake line during pre-trip. Walk the full length of each air hose and tubing run on your tractor and trailer. Look for contact wear where lines pass near the frame, suspension components, or exhaust. FRHT, KW, VOLV, PTRB, and INTL makes account for the majority of 393.45D citations in our database — if you're in one of these cabs, know where your chassis routes brake lines close to high-wear areas.
- Squeeze and flex hoses at connection points. Crimped or collapsing hoses may look intact until you manipulate them. Apply light hand pressure to feel for stiffness, soft spots, or internal restriction near couplings and glad hands.
- Check for chafing at any point where a hose runs adjacent to a moving part. Steering linkage, driveshaft, and suspension contact points are the most common culprits. A hose that looks fine when the vehicle is stationary may be rubbing under load.
- Inspect slack adjusters at the same time. Our 90-day data shows 393.47E co-occurring with 393.45D 27 times. Slack adjuster condition and hose condition are both brake-system indicators — if one is off, inspect the other thoroughly.
- Verify your periodic inspection documentation is current and on board. No proof of periodic inspection (396.17C) appeared alongside 393.45D 30 times in the last 90 days. An expired or missing inspection sticker signals to an inspector that brake system maintenance may be overdue, increasing scrutiny on exactly the components covered by 393.45D.
- Don't skip lighting checks on the same pre-trip pass. 393.9 (Inoperable Required Lamp) co-occurred with 393.45D 40 times in the last 90 days — the most common pairing in our data. An inoperable lamp is often what triggers a more thorough inspection that surfaces the brake hose defect.