What a DOT Inspection Actually Tests
Commercial vehicle inspections conducted by enforcement officers follow the Commercial Vehicle Safety Alliance (CVSA) North American Standard inspection program, which draws its out-of-service criteria from FMCSA 49 CFR Part 393 (Parts and Accessories Necessary for Safe Operation) and Part 396 (Inspection, Repair, and Maintenance). The Level I inspection — a full vehicle and driver inspection — is the most comprehensive. Level II and III inspections cover subsets of the same criteria. The CVSA program includes eight inspection levels. Level IV covers special study inspections; Level V is a vehicle-only inspection without a driver; Level VI covers HRCQ radioactive material shipments; Level VII covers jurisdiction-specific programs; and Level VIII is a wireless electronic inspection conducted while the vehicle is in motion.
For medium-duty commercial fleets operating in Texas and the surrounding region, annual inspections are mandatory, and roadside inspections can happen any time the truck is on a public road. A truck placed out of service at roadside costs far more than the fine alone — it means a driver waiting for either a repair to be made on-site or a tow to a shop, lost work hours, and in some cases missed project deadlines.
The best way to avoid a roadside out-of-service order is a systematic pre-inspection routine before any truck goes on the road. What follows is the walk-around sequence we use.
Service Brakes and Brake System
Brakes are the single most common reason commercial vehicles receive out-of-service orders under CVSA criteria. The inspector will measure brake lining thickness and check for cracked or missing hardware. You should too.
Pre-inspection checks:
- Lining thickness — FMCSA 393.47(d)(1) sets steering axle OOS thresholds at less than 3/16 inch (4.8 mm) for shoes with a continuous strip of lining (the most common S-cam drum configuration), or less than 1/4 inch (6.4 mm) for shoes with two pads. Non-steering air drum brakes must be at or above 1/4 inch (6.4 mm). Measure with a gauge, not a visual estimate.
- Air brake systems — If the vehicle uses air brakes, check system pressure build-up time, governor cut-out pressure, and low-pressure warning indicator function. Check air lines for chafing, cracking, or contact with hot components.
- Slack adjusters — Automatic slack adjusters that are out of adjustment are an out-of-service item. Push-rod travel limits vary by chamber size, ranging from 1¼ inch for smaller chambers to 2 inches for long-stroke (LS) chambers. Always verify against the applicable chamber size in the CVSA push-rod stroke table — do not use a 2-inch rule of thumb across all configurations.
- Brake drums and rotors — Cracked drums are an immediate out-of-service condition. Check for scoring depth on rotors if the vehicle uses disc brakes.
Tires and Wheels
Pre-inspection checks:
- Tread depth — Under 49 CFR 393.75, front/steer tires on trucks and truck-tractors must have at least 4/32-inch tread depth; all other tires must have at least 2/32-inch. CVSA out-of-service criteria are slightly less stringent: steer tires go OOS at less than 2/32-inch in two adjacent grooves, and other tires at less than 1/32-inch in two adjacent grooves at three circumferential locations. Inspect across the full width of the contact surface, not just the center groove.
- Tire pressure — Under-inflation is an out-of-service condition when inflation is less than 50% of the maximum inflation pressure marked on the tire sidewall (per 49 CFR 393.75(a)(3)). Beyond the OOS threshold, chronic under-inflation damages tires, increases fuel consumption, and is one of the primary contributors to tire failure on hot pavement.
- Sidewall condition — Any fabric break, bump, bulge, or cut that exposes the ply or belt is an immediate OOS condition.
- Wheel fasteners — Loose or missing lug nuts are an OOS condition. Check for rust streaking from wheel stud holes, which indicates movement.
- Dual spacing — On dual-tire configurations, check that spacing is adequate and that no tire is making contact with its pair.
Lighting and Electrical Systems
Lighting failures are common and often go unnoticed until enforcement finds them. A complete lighting check takes under five minutes with a second person or a reflective surface to check rears.
Lights to verify:
- Headlights (both high and low beam)
- Tail lights, brake lights, and reverse lights
- Turn signals, front and rear
- Hazard flashers
- Side marker lights and clearance lights on Class 6+ trucks
- License plate illumination
- Any work lights, amber strobes, or auxiliary lighting that is required for the truck's operating role
For TMA trucks specifically, the amber warning lights, arrow board circuits, and any integrated lighting on the attenuator must also function. These aren't FMCSA inspection items per se, but they are required operational equipment for work-zone deployment and are subject to review by state DOT enforcement in Texas.
Steering, Suspension, and Frame
Steering:
- Check steering wheel free play — excess free play (more than the manufacturer-specified limit, generally around 2 inches measured at the rim on a large wheel) is an OOS condition.
- Inspect tie rod ends and drag link for looseness. Grab and rock the tire to check for play at steering components.
- Inspect the power steering system for fluid level and visible leaks.
Suspension:
- Look for cracked or missing leaf spring leaves. Any cracked spring is an OOS condition.
- Check U-bolt torque — loose U-bolts are common on trucks operating in work-zone start/stop duty.
- Inspect shock absorbers for active fluid leaks.
Frame:
- Walk the frame rails fore and aft. Cracked frame rails, missing crossmembers, or loose body mounts are all OOS conditions.
- For TMA trucks, give extra attention to the rear frame section where the attenuator mounting subframe attaches.
Fuel System, Exhaust, and Engine Compartment
Fuel system:
- Inspect fuel tanks for visible leaks. Even a seeping tank fitting is an OOS condition.
- Check that tank mounting brackets and straps are secure.
- Inspect fuel lines for chafing or heat damage near the exhaust system.
Exhaust:
- The exhaust system must be leak-free forward of the cab or any enclosed area. Exhaust leaks at manifold joints, flex sections, or EGR connections are both an OOS condition and an operating hazard.
- Check the DEF tank and lines on post-2010 diesels. A DEF system fault that induces engine derate does not create an immediate OOS, but it will create a problem before the truck reaches its destination.
Engine compartment:
- Check coolant level and look for leaks at hoses, the thermostat housing, and water pump.
- Check oil level.
- Inspect belts for glazing, fraying, or cracking.
- Look for any active fault codes on the dash — particularly emissions-related codes that may indicate a DPF issue developing.
The Eight Categories That Generate the Most OOS Orders
CVSA annual inspection data consistently shows that most out-of-service orders come from a relatively short list of conditions. For medium-duty fleets, the most common are:
- Brake lining thickness below threshold
- Air brake adjustment (slack adjuster out of adjustment)
- Tire tread depth or sidewall damage
- Inoperative lights (brake lights and tail lights most common)
- Cracked or leaking fuel tanks
- Broken or missing leaf spring leaves
- Inoperative or missing required emergency equipment (fire extinguisher, warning triangles)
- Windshield defects in the driver's line of sight (less common but frequently cited)
A driver-level pre-trip inspection — required under FMCSA 396.13 for all drivers of commercial motor vehicles subject to 49 CFR Part 396 — should catch most of these. The shop-level inspection at each PM service should catch what drivers miss.
Coupling Devices (Where Applicable)
For medium-duty trucks towing trailers — which includes many service configurations and TMA setups with towed equipment — the coupling inspection is critical:
- Fifth wheel: check for missing or loose mounting bolts, cracks in the fifth wheel casting, and proper locking jaw engagement.
- Pintle hook or ball hitch: check for wear in the hook's locking mechanism, proper safety chain attachment, and working breakaway cable if required.
- Electrical connection: test all trailer lighting functions at the connector before departure.
Our fleet services team performs annual DOT inspections and pre-inspection walk-arounds for medium-duty fleets across North Texas and the DFW Metroplex, including mobile service at your yard.
Talk to us
If you want a qualified shop to perform a DOT inspection or pre-inspection review on your fleet, call (940) 600-5131 or schedule through our contact form.