What to Check Before You Drive a Commercial Vehicle

What a commercial vehicle inspection covers

A commercial vehicle inspection is a safety check you perform before operating the vehicle. In South Carolina, the Department of Motor Vehicles requires commercial vehicle owners to maintain their trucks in safe operating condition, and many inspections are documented for compliance and insurance purposes. The inspection itself is not a government test you submit to — it is a hands-on walkthrough of the vehicle's critical systems that you or a may have access to mechanic complete.

The inspection covers the engine, brakes, tires, lights, steering, coupling devices (if applicable), and safety equipment. Some items must be checked daily before driving; others are part of a more thorough weekly or monthly review. The goal is to catch problems before they become safety hazards or cause breakdowns that cost you time and money.

If your fleet operates under Department of Transportation (DOT) regulations — which applies if you haul certain cargo or cross state lines — you will need to document these inspections. Even if DOT rules do not apply to your operation, keeping records of what you checked and when protects you if an accident occurs and someone questions whether the vehicle was maintained properly.

Key Takeaways

• Daily pre-trip inspections should take 15 to 30 minutes and cover brakes, tires, lights, steering, and safety equipment before the vehicle leaves the lot.
• Weekly or monthly inspections go deeper, checking fluid levels, hose condition, coupling devices, and structural damage that daily checks might miss.
• DOT-regulated vehicles require written inspection reports; even if your operation is not DOT-regulated, written records protect you legally.
• Many insurance companies offer discounts if you maintain documented inspection records, and some require them as a condition of coverage.
• A failed inspection item should be repaired before the vehicle returns to service, and the repair should be documented alongside the original inspection report.

Daily pre-trip inspection items

Before each shift, walk around the vehicle and check the items that affect immediate safety. Start with the tires: look for uneven wear, bulges, cuts, or tread depth below 4/32 of an inch (use a penny inserted into the tread as a rough gauge). Check that all tires are inflated to the pressure listed on the driver's door jamb or in your owner's manual, not the maximum pressure on the tire itself.

Next, inspect all lights: headlights, taillights, brake lights, turn signals, and clearance lights if your vehicle is over 80 inches wide. Turn them on and walk the perimeter to confirm each one works. Check the windshield and mirrors for cracks or damage that blocks visibility. Look at the windshield wipers and washer fluid level.

Test the brakes by pressing the pedal firmly while the vehicle is parked and listening for unusual sounds. If you have air brakes, check the air pressure gauge and listen for air leaks. Verify that the steering wheel moves smoothly without excessive play or grinding sounds. Check that all doors close securely and latches hold. Look under the vehicle for leaks of oil, coolant, brake fluid, or fuel — a small puddle under the engine is normal after a long run, but a fresh leak is not.

Confirm that safety equipment is present and accessible: fire extinguisher, spare fuses, spare belts, warning triangles or flares, and a first aid kit if required by your insurance or company policy. If your vehicle has a coupling device (fifth wheel or pintle hook), inspect it for cracks, loose bolts, or corrosion.

Weekly and monthly inspection items

Once a week, perform a more thorough check that includes items the daily inspection does not cover. Open the hood and check fluid levels: engine oil, coolant, brake fluid, power steering fluid, and windshield washer fluid. Top off any that are low. Look at hoses and belts for cracks, fraying, or loose clamps. A cracked hose or worn belt can fail without warning and leave you stranded.

Inspect the battery terminals for corrosion (a white or blue-green crusty buildup) and tighten any loose connections. Check that the battery is secure in its mounting bracket. Look at the alternator and starter for loose bolts or signs of damage.

Once a month, get under the vehicle (safely, on a lift or with proper jack stands) and inspect the suspension components: springs, shocks, and U-bolts for cracks or looseness. Check brake lines and hoses for leaks, cracks, or abrasion. Inspect the frame for cracks or rust that has eaten through the metal. Look at the exhaust system for loose hangers, holes, or damage.

Check the cargo area or truck bed for damage, rust, or loose tie-down points. If you haul a trailer, inspect the trailer's tires, lights, brakes, and coupling connection. Verify that all safety chains or cables are present and secure.

How to document inspections

If your operation is DOT-regulated, you must keep written inspection reports. The report should include the date, time, vehicle identification number (VIN), odometer reading, driver name, and a list of items checked with a pass or fail mark for each. Any item that fails must be noted with a description of the defect — for example, "left rear tire tread 2/32 inch" or "brake light not functioning."

The driver who performed the inspection should sign and date the report. If a defect is found, the report must be given to the vehicle owner or maintenance supervisor, and the defect must be repaired before the vehicle is used again. Once repaired, the mechanic should sign off on the repair and note the date and mileage.

Even if DOT rules do not apply to your fleet, keeping the same type of written record is wise. Many insurance companies ask to see inspection records when you file a claim, and a documented history of maintenance protects you if someone argues the vehicle was not properly maintained. Store records for at least one year, organized by vehicle and date.

You can use a paper form, a spreadsheet, or a fleet management app — the format does not matter as long as the information is clear and complete. Some fleet owners photograph defects (a tire with low tread, a cracked light lens) and attach the photo to the report for clarity.

What to do when you find a defect

If an inspection reveals a problem, do not ignore it or defer the repair. A failed brake, a bald tire, or a broken light is a safety hazard and a legal liability. If the vehicle is DOT-regulated, operating it with a known defect can result in fines and out-of-service orders that ground the vehicle until repairs are made.

Assign the repair to a may have access to mechanic as soon as possible. If the defect is minor and can be fixed quickly (a burned-out bulb, a loose bolt), repair it before the next shift. If the repair is complex (brake work, engine diagnostics), schedule the vehicle for maintenance and use a backup vehicle if you have one. Document the repair with the date, mileage, parts replaced, and mechanic's signature.

If a driver reports a defect during a shift and you cannot repair it immediately, remove the vehicle from service. Do not ask the driver to continue operating an unsafe vehicle, and do not allow another driver to take it out. The cost of a repair is far less than the cost of an accident, a fine, or a lawsuit.

Inspection requirements for DOT-regulated vehicles

If your commercial vehicles are subject to DOT regulations — which typically applies if you haul hazardous materials, carry passengers, or operate across state lines — you must follow specific inspection rules. The Federal Motor Carrier Safety Administration (FMCSA) requires that vehicles be inspected before each day of operation and that defects be documented in writing.

DOT inspections are more detailed than general safety checks. They include examination of the coupling system, brake performance, steering, lighting, and cargo securement. If an inspection uncovers a defect that makes the vehicle unsafe, it must be repaired and verified before the vehicle returns to service.

The FMCSA also conducts roadside inspections of commercial vehicles. If an inspector finds violations of maintenance or inspection rules, the vehicle can be placed out of service until repairs are made, and you may face fines. Keeping thorough inspection records demonstrates that you are taking maintenance seriously and can reduce penalties if a violation is found.

Contact the South Carolina Department of Motor Vehicles or the FMCSA website to confirm whether your operation is DOT-regulated. If you are unsure, assume it is — the rules are designed to protect public safety, and compliance is not optional.

Common inspection failures and how to prevent them

Tire defects are the most common inspection failure. Tires wear unevenly if the vehicle is not aligned properly, if tire pressure is not maintained, or if the suspension is damaged. Check tire pressure weekly and have the alignment checked annually. Replace tires before they reach the legal minimum tread depth of 2/32 inch; many fleet operators replace at 4/32 inch to avoid unexpected failures.

Brake problems are the second most common failure. Brake fluid should be clear; if it is dark or cloudy, it has absorbed moisture and should be flushed. Brake pads should be inspected monthly and replaced before they wear through to the rotor. Air brake systems should be tested for leaks and proper pressure. If you hear grinding, squealing, or a soft pedal, have brakes inspected immediately.

Lighting failures are easy to prevent: check all lights weekly, replace burned-out bulbs immediately, and keep spare bulbs and fuses on hand. Corroded or loose connections can cause lights to fail intermittently; clean and tighten connections during monthly inspections.

Fluid leaks often indicate worn seals or loose fittings. Small leaks can be tightened; larger leaks require component replacement. Do not ignore leaks — they worsen quickly and can cause catastrophic failure if the fluid level drops too low.

Frequently Asked Questions

How often should I inspect a commercial vehicle?

Daily pre-trip inspections are required before each shift. Weekly inspections should cover fluid levels and hose condition. Monthly inspections should include suspension, brakes, and frame inspection. If your vehicle is DOT-regulated, daily written inspections are mandatory; if not, written records are still recommended for insurance and legal protection.

Can a driver perform the inspection, or does a mechanic have to do it?

Drivers can and should perform daily pre-trip inspections — they are trained to spot obvious problems and take responsibility for the vehicle's condition. Weekly and monthly inspections can be done by a may have access to driver or a mechanic. DOT regulations require that the person performing the inspection be able to identify defects; if you are unsure whether a driver has that skill, have a mechanic do the inspection.

What happens if I operate a vehicle with a known defect?

If the vehicle is DOT-regulated, you face fines and the vehicle can be placed out of service. If an accident occurs and the defect contributed to the accident, your insurance may deny the claim and you could be held personally liable. Operating an unsafe vehicle is never worth the risk.

Do I need to keep inspection records forever?

DOT regulations require records to be kept for at least one year. For legal protection, keep records for at least three years in case of a lawsuit or insurance claim. After that, you can discard them unless your insurance company requires a longer retention period.

What if I cannot afford to fix a defect right away?

Remove the vehicle from service until the repair is made. If you have multiple vehicles, use a backup while the defective one is being repaired. The cost of a repair is far less than the cost of an accident, a fine, or a lawsuit. If cash flow is tight, prioritize safety-critical repairs (brakes, tires, steering) over cosmetic ones.