Top 7 Preventive Maintenance Gaps That Lead to Failed DOT Inspections

DOT Inspections Don’t Forgive Neglect

The Department of Transportation (DOT) doesn’t hand out warnings when your truck misses the mark—they hand out citations, out-of-service orders, and lost driving hours. But the frustrating truth for many fleet owners and drivers is that most DOT violations aren’t caused by major mechanical failures. They’re caused by small, preventable gaps in maintenance.

At Myles Truck Repair, we see the same culprits show up again and again during roadside inspections and compliance audits. Whether you manage a fleet or run your own rig, these overlooked issues can spell serious trouble. In this post, we’ll walk through the top 7 preventive maintenance (PM) gaps that lead to failed DOT inspections—and how to close them for good.

1. Brake System Issues

Why It Happens

DOT officers frequently cite trucks for brake adjustment, worn pads, air leaks, or out-of-adjustment slack adjusters. Many operators assume “if it stops, it’s fine”—but that’s a costly misconception. Even minor differences in brake stroke can cause the entire vehicle to be flagged.

What to Do

• Check brake stroke and adjustment regularly
  
  
• Drain air tanks to prevent moisture buildup
  
  
• Inspect for cracked drums, worn linings, and leaking wheel seals
  
  
• Grease slack adjusters and confirm they’re working automatically
  
  
• Include brake function in your pre-trip and BIT inspection routine
  
  

2. Lighting and Electrical Failures

Why It Happens

Malfunctioning marker lights, missing reflectors, and corroded connectors are quick DOT targets. Moisture and vibration take a toll on lighting systems, especially trailers that see winter road salt or off-road use.

What to Do

• Test all exterior lights during daily pre-trips
  
  
• Use dielectric grease on plug connectors
  
  
• Replace corroded or exposed trailer wiring
  
  
• Confirm that all reflectors and conspicuity tape are intact and visible
  
  
• Add lighting checks to every PM interval and repair as needed
  
  

3. Tire and Wheel Condition

Why It Happens

DOT requires a minimum tread depth (4/32” on steer tires, 2/32” elsewhere). But inspections don’t stop at tread—they check inflation, mismatched sizes, sidewall bulges, and visible cords. Wheels are also inspected for cracks, missing lug nuts, and rust jacking.

What to Do

• Use tread depth gauges, not just visual inspection
  
  
• Monitor tire pressure weekly
  
  
• Inspect inside duals during every service
  
  
• Check for rim cracks, missing lug nuts, and signs of loose studs
  
  
• Replace aged or weather-cracked tires, even if they still have tread
  
  

4. Suspension and Steering Wear

Why It Happens

DOT checks for worn bushings, loose kingpins, cracked springs, and excessive steering wheel play. Many of these issues build slowly over time and may not feel dramatic to the driver—until an officer gets under the frame with a pry bar.

What to Do

• Regularly inspect spring packs, hangers, and U-bolts
  
  
• Raise the axle and test for kingpin movement
  
  
• Replace leaking or worn-out shocks
  
  
• Check that steering lash is within regulation
  
  
• Include steering/suspension checks in 90-day PMs or BIT Inspections
  
  

5. Fluid Leaks and Underbody Contamination

Why It Happens

DOT does not allow active leaks from oil, coolant, fuel, or brake fluid systems. Even small seeps can trigger a citation if they’re visible, especially near brakes, driveline components, or electrical systems.

What to Do

• Steam-clean the undercarriage before inspections
  
  
• Replace worn gaskets, hoses, or seals at the first sign of seepage
  
  
• Track fluid consumption between services—if you’re topping off, you’re leaking
  
  
• Check hydraulic and DEF systems for seepage as well
  
  

6. Exhaust and Emissions Equipment

Why It Happens

Cracked DPF housings, disconnected EGR tubes, and leaking exhaust manifolds can cause failed inspections and out-of-service violations, especially in states with emissions enforcement programs. Missing heat shields or visibly tampered components are also flagged.

What to Do

• Inspect for soot trails near clamps or joints
  
  
• Verify DPF and SCR systems are intact and mounted properly
  
  
• Don’t ignore active regen warnings or check engine lights
  
  
• Keep OEM heat shielding in place
  
  
• Have your emissions system scanned during every PM
  
  

7. Documentation and Inspection Recordkeeping

Why It Happens

DOT audits don’t just check the vehicle—they check your paperwork. Missing pre-trip inspection logs, outdated annuals, or incomplete repair records are enough to trigger fines or audit failures, even if your truck is mechanically sound.

What to Do

• Keep driver vehicle inspection reports (DVIRs) in the cab
  
  
• Maintain up-to-date annual inspection certificates
  
  
• Log all BIT inspections every 90 days
  
  
• Track PMs by mileage or engine hours—not guesswork
  
  
• Use fleet software or binders to organize inspection history and service logs
  
  

Why Preventive Maintenance Matters for Compliance

DOT inspectors aren’t out to fail good drivers. What they want to see is that your vehicle is safe, roadworthy, and well-maintained. Preventive maintenance isn’t just about avoiding repair bills—it’s about building a record of diligence and responsibility.

At Myles Truck Repair, we help fleet operators and owner-operators stay ahead of inspections with data-driven PM schedules, checklist documentation, and complete vehicle evaluations.

Bonus: How BIT Inspections Tie In

For fleets operating in California, BIT inspections are required every 90 days. This state-mandated PM system covers many of the same items as DOT inspections, including:

• Brake system components
  
  
• Steering and suspension integrity
  
  
• Tire and wheel condition
  
  
• Lights and reflective tape
  
  
• Exhaust leaks and mountings
  
  

Falling behind on BIT inspections increases your risk of failing roadside DOT stops—especially if you’re flagged during a pull-over or after a weigh station check.

How to Build a PM Program That Passes Inspections

Step 1: Use Checklists

Create a comprehensive PM checklist for each vehicle class in your fleet. Include specific intervals and components based on manufacturer specs, operating environment, and duty cycle.

Step 2: Schedule Inspections Smartly

Don’t rely on memory or guesswork. Use telematics, fleet maintenance software, or manual logs to schedule inspections and services based on mileage, engine hours, or calendar time.

Step 3: Train Your Drivers

Drivers are your first line of defense. Train them to conduct thorough pre-trip inspections, report faults, and understand which issues can lead to an OOS violation.

Step 4: Keep Records Clean

Your PMs, repairs, inspections, and follow-up actions should be well-documented and accessible. DOT audits often ask for proof of repairs or inspection history.

Step 5: Partner with the Right Shop

Choose a repair partner that understands DOT and BIT inspection criteria. At Myles Truck Repair, we perform PM services, offer inspection simulations, and help prepare documentation to pass real-world audits.

Final Thoughts

Failed DOT inspections often stem from missed maintenance—not major malfunctions. By closing these seven common PM gaps, you reduce the risk of violations, improve vehicle safety, and show regulators that your fleet takes compliance seriously.

Whether you manage five trucks or fifty, the key to passing every inspection is simple: stay ahead of wear, keep your records clean, and partner with a shop that knows the rules inside and out.

Ready to review your PM strategy? Contact Myles Truck Repair today—we’ll help you build an inspection-ready fleet from the ground up.