Vehicle Maintenance Violations That Most Often Ground a Truck

Vehicle Maintenance is typically the BASIC category with the highest overall violation volume, and it's not hard to see why: a physical inspection of a commercial vehicle can surface dozens of possible mechanical issues, from serious brake defects to a burned-out marker light. Understanding which defects come up most often — and which ones actually result in an out-of-service order versus a citation to fix later — helps put a carrier's vehicle maintenance record in context.

Brake systems

Brake-related defects are consistently among the most common and most serious findings in vehicle inspections. Inspectors check brake adjustment, condition of brake components, and overall system function, because a compromised braking system is one of the most direct contributors to a vehicle being unable to stop safely. Significant brake defects are a common trigger for an immediate out-of-service order rather than a fix-it-later citation.

Tires

Worn tread depth, visible damage, improper inflation, and mismatched tires on the same axle are all checked during inspection. Tire condition affects both stopping distance and stability, particularly relevant for heavy vehicles carrying significant loads, and defects here are common enough to represent a substantial share of vehicle-related findings.

Lighting and electrical

Non-functioning headlights, brake lights, turn signals, or marker lights are frequently cited findings — often less severe individually than a brake defect, but still safety- relevant, especially for visibility in low-light or poor-weather conditions, and cheap enough to fix that a pattern of lighting violations can suggest inconsistent pre-trip inspection practices rather than a one-off oversight.

Steering and suspension

Excessive play in steering components, damaged or missing suspension parts, and related defects affect a vehicle's handling and stability. These are checked as part of a comprehensive inspection and, depending on severity, can be serious enough to warrant an out-of-service order.

Coupling devices

For combination vehicles — a tractor pulling a trailer — the condition of the coupling system connecting the two is inspected specifically, since a failure here can result in trailer separation, one of the more catastrophic mechanical failure modes on the road.

Why maintenance patterns matter more than a single defect

Any individual vehicle can develop a defect between scheduled maintenance intervals — that alone doesn't indicate a poorly run fleet. What's more informative is a pattern across multiple inspections and multiple vehicles within the same carrier: a consistently elevated vehicle out-of-service rate suggests something systemic about how the fleet is maintained, rather than isolated bad luck. See What an Out-of-Service Rate Says About a Carrier for how to read that rate in context, and Reading an Inspection Report: Levels 1–6 for which inspection levels actually check vehicle condition.

Checking a carrier's vehicle maintenance record

A carrier's profile, available through DOT Number Lookup, shows the vehicle out-of-service rate over the trailing 24 months and how it compares to the national median for carriers with a similar number of inspections.