Top 5 Reasons Trucks Fail DOT Inspections

To help fleet managers and drivers stay proactive, here are the top 5 reasons trucks fail DOT (Department of Transportation) inspections.

Brake System Violations

Brakes are the most frequently cited component during DOT inspections—and with good reason. A semi-truck’s brake system is its most critical safety mechanism, but it’s also one of the most complex. DOT inspectors routinely check for worn brake pads, contaminated linings, cracked brake drums, and air leaks.

Example: Slack adjusters, for instance, are often found to be out of spec. These small but mighty components compensate for brake shoe wear and must maintain proper pushrod travel. If an inspector spots a brake stroke that exceeds acceptable limits or finds an air leak in the service chambers, the truck is coming off the road.

Actionable Tip:

Perform a weekly brake stroke test. Use a brake stroke gauge to measure pushrod travel. Train drivers to identify warning signs like a spongy brake pedal or air compressor cycling too frequently.

Tire and Wheel Infractions

DOT inspectors are hawk-eyed when it comes to tires—and for good reason. A blown tire at 65 mph can spell disaster. Trucks routinely fail inspections due to:

• Insufficient tread depth (less than 4/32" on steer tires)
• Sidewall damage
• Mismatched tire types

Wheels are another common offender. Cracked rims, missing lug nuts, or improper torque on studs can lead to wheel separation—a catastrophic and preventable failure.

Actionable Tip:

Use a tread depth gauge during pre-trip inspections and never assume visual checks are enough. Rotate and balance tires regularly, and re-torque wheel assemblies after installation.

Lighting and Reflector Deficiencies

Don’t underestimate the importance of lights and reflectors. From inoperable turn signals to missing reflective tape, lighting violations are among the easiest to spot—and the easiest to prevent.

Trucks are required to have fully operational clearance lights, brake lights, tail lights, and license plate illumination. Any malfunction—no matter how small—can flag a violation.

In fact, improper or missing conspicuity tape along the trailer’s side or rear can lead to an automatic failure.

Actionable Tip:

Conduct daily walkarounds with lights turned on. Confirm every signal functions correctly and replace bulbs immediately. Always carry spares and fuses in your cab.

Suspension System Failures

A truck’s suspension system does more than just keep the ride smooth—it bears the weight of the load and protects critical drivetrain components. DOT inspectors are trained to check for:

• Cracked leaf springs
• Air bag leaks
• Worn bushings
• Misaligned axles

One overlooked area is the shock absorber mounts. If these mounts are rusted through or broken, they compromise the entire suspension integrity and invite a quick out-of-service order.

Actionable Tip:

Check for uneven ride height and visible damage around the leaf spring hangers or air ride bags. Listen for air leaks around your suspension during post-trip inspections.

Fluid Leaks and Engine Compartment Issues

DOT inspectors will thoroughly examine under the hood. Common red flags include oil leaks, fuel seepage, and coolant residue. A leak doesn’t have to be severe to warrant a violation—if it's visible and unaddressed, it’s enough to fail.

Another frequent infraction involves loose or frayed belts and hoses. The serpentine belt, which powers components like the alternator and water pump, must be in good condition and properly tensioned.

Actionable Tip:

Inspect your engine bay weekly. Clean any oil or fluid drips promptly to monitor future leaks. Tighten hose clamps and replace cracked belts before they snap.

Stay Proactive With Your Maintenance

Failing a DOT inspection is not only a regulatory nightmare but also a hit to your business's reputation. The most common violations—brakes, tires, lights, suspension, and fluid leaks—are preventable with routine checks and proper driver training. A well-maintained truck not only passes inspections but ensures safer roads for everyone.

If you require a DOT inspection in Mt Nebo, WV, contact AMF Enterprises today!