§393.48 is the foundational brake-condition rule: all brakes with which a CMV is equipped, including those of any towed vehicle, must be operative at all times. The rule sits behind §393.47 (adjustment), §393.52 (performance), and the §393.42–§393.46 design requirements — a brake that fails any of these is also "inoperative" under §393.48.
OOS
A brake counts toward the 20% OOS threshold if it is missing, broken, disconnected, contaminated with oil or grease, or otherwise inoperative. When 20% or more of the brakes on the vehicle are defective, the vehicle is OOS under the NAS Out-of-Service Criteria.
Severity weight
Severity weight 4 in the Vehicle Maintenance BASIC. The weight rises when a §393.48 finding is cited together with §393.47 (out of adjustment) and §393.52 (performance) — the cluster, not the single weight, is what moves the percentile.
How to prevent it
- Treat any oil- or grease-contaminated brake as inoperative — the seal failure usually predates the contamination.
- Replace shoes and drums together when wear is uneven; preserve the wheel-end as a unit.
- A disconnected air line, kinked hose, or stuck push rod all count as "inoperative" — pre-trip air-brake test catches most of these.
How Roadworthy HQ helps
§393.48 findings logged in Roadworthy HQ link to the vehicle alongside §393.47 and §393.52 findings so the wheel-end-by-wheel-end picture is visible. Dispatch is blocked under §396.11(c) until §396.9(d)(3) repair certification is on file.