DOT Inspection Checklist for Commercial Trucks

Every commercial motor vehicle operating under FMCSA authority needs a periodic inspection at least once every 12 months, under 49 CFR § 396.17. That's separate from the roadside inspections a state trooper or DOT officer can perform at any time — the periodic inspection is a scheduled, thorough check that produces documentation you keep on file. This checklist covers what a proper inspection actually looks at, so you know what to check before it's due.

Brake system

Brakes are the single most common reason a truck or trailer gets placed out of service. An inspector checks:

• Brake adjustment on every axle, within spec for the slack adjuster type
• Air or hydraulic lines for leaks, cracking, or chafing
• Brake chambers, drums or rotors, and linings for wear or damage
• The low-air-pressure warning system and spring brake (parking brake) function

Steering and suspension

• Steering wheel free play and the steering column, gear box, and linkage
• Springs, shocks, and mounting hardware for cracks, breaks, or missing parts
• Axle positioning — nothing shifted or out of alignment

Lighting and electrical

Every required lamp has to work and be the correct color: headlamps, tail lamps, brake lamps, turn signals, and marker/clearance lamps on both the tractor and trailer. A single burned-out marker light is an easy, avoidable out-of-service violation.

Tires and wheels

• Tread depth — 4/32" minimum on steer axle tires, 2/32" on others
• No visible cord, sidewall damage, or improper repairs
• Wheel and rim condition, and lug nut torque/condition

Coupling devices

Fifth wheel, kingpin, and locking mechanism condition on tractor-trailer combinations, plus the safety chains or equivalent on pintle-hitch setups.

Frame, body, and exhaust

The inspector also checks the frame for cracks or visible repairs, the exhaust system for leaks that could route fumes into the cab, and — for the tractor — the windshield, wipers, mirrors, and horn.

Getting ready before yours is due

The best time to catch a brake or lighting issue is before an inspector finds it. If it's been close to 12 months, or you're not sure when the last inspection was documented, a pre-check against this list — and repairs handled the same visit — is usually faster and cheaper than dealing with an out-of-service violation later.