5 Things That Will Fail a DOT Trailer Inspection

Every time a trailer hits the road, it’s subject to potential roadside inspection — and when something fails, it’s not just a citation. It’s downtime, CSA points, and a potential safety risk. While there are dozens of potential violations, a handful of issues show up again and again.

Here are five of the most common DOT trailer inspection failures — and how your shop can prevent them.

. Non-Functioning Lights

Lighting violations are one of the most frequently cited issues in trailer inspections. Missing or non-functioning brake lights, turn signals, or marker lamps are easy for DOT officers to spot and will lead to immediate citation.

Prevent It: Use automated light testers like the Pro-Check 720 to check every circuit for power and integrity — not just whether the lights turn on.

2. Air Brake System Leaks

DOT inspectors routinely check the trailer’s air system for pressure retention and leak rates. Even minor leaks or faulty valves can fail an inspection and require immediate OOS (out-of-service) designation.

Prevent It: Integrate air system testing into every PM using a diagnostic tool capable of leak detection and valve performance analysis.

3. ABS Faults

A lit ABS warning lamp, missing diagnostic response, or faulty sensors will cause a trailer to fail inspection. Many ABS faults are intermittent or tied to wiring issues — making them easy to miss in visual checks.

Prevent It: Run an ABS diagnostic using tools like the Inspector 930 to pull fault codes and confirm system readiness.

4. Exposed or Damaged Wiring

Loose, exposed, or corroded wiring is another top reason for failure. Inspectors will flag trailers with compromised harnesses, damaged connectors, or signs of insulation wear — especially around junction boxes and rear lighting assemblies.

Prevent It: Conduct regular trailer wiring inspections with attention to plug integrity, wire routing, and proper grounding.

5. Tire and Brake Wear

While not electrical, this is one failure that shows up often and can sideline an otherwise roadworthy trailer. Bald tires, low tread depth, and out-of-adjustment brakes are a direct path to OOS status.

Prevent It: Ensure your PM schedule includes clear criteria for tire and brake wear thresholds — and that inspections are documented properly.

Don’t Leave Inspections to Chance

DOT trailer inspection failures are costly, but they’re preventable. Shops that implement systematic diagnostics with automated testing tools can eliminate guesswork and reduce roadside violations significantly.

Explore tools like the Inspector 930 to run lighting, ABS, and air brake diagnostics — all in one process.

For more on how Lite-Check helps fleets pass inspections with confidence, visit Lite-Check.com, call 509-535-7512, or email info@lite-check.com.