What Does a Pre-Purchase Semi Truck Inspection Include?
A complete breakdown of the eight inspection categories, what an ECM scan reveals, and how to read your Sell My Rig report before buying a used semi.
A pre-purchase semi truck inspection from Sell My Rig Inspections covers eight categories: engine and powertrain, transmission and drivetrain, brakes and suspension, tires and wheels, frame and structural, electrical and lights, cab and interior, and documents and VIN. The inspector pulls ECM fault codes through the J1939 port, measures brake lining and tread depth with calipers, photographs 200+ checkpoints, and delivers the full report the same day for $350 flat.
The 8 categories explained
A thorough semi truck inspection is organized into eight categories so nothing gets missed.
- Engine & Powertrain — ECM diagnostic scan, fault codes, DPF/DOC/SCR aftertreatment status, oil and coolant condition, turbo boost, and air filter.
- Transmission & Drivetrain — shift quality through all gears, clutch, driveshaft and U-joints, differential seals, and axle condition.
- Brakes & Suspension — brake lining depth measured with calipers, drum condition, chambers and slack adjusters, air leak-down test, shocks, springs, and steering.
- Tires & Wheels — tread depth in 32nds at every position, brand, size, age, sidewall condition, wheel cracks, and lug torque.
- Frame & Structural — frame rails, crossmembers, fifth wheel, accident damage, and rust.
- Electrical & Lights — battery load test, alternator output, all running lights, wiring harness, and instrument cluster.
- Cab & Interior — HVAC, sleeper, door seals and glass, seats, gauges, and controls.
- Documents & VIN — VIN verification against the door placard, GVWR and engine stickers, NMVTIS title history, NHTSA recall check, and odometer disclosure.
What an ECM scan tells you
The ECM (Engine Control Module) scan connects to the J1939 diagnostic port and pulls every stored and active fault code, plus aftertreatment status. This is the single most valuable part of the inspection because it surfaces hidden engine problems and tampered data a visual check can never catch.
Why tread depth matters in 32nds
Tread depth is measured in 32nds of an inch at every tire position. Steer tires are legal down to 4/32" and other positions to 2/32". Documenting each position tells you how much tire life you are actually buying and whether uneven wear points to an alignment or suspension problem.
What the inspector checks vs. what they don't
Sell My Rig inspectors report observable, measurable condition. They do not provide a pass/fail grade or guarantee future reliability — they give you the data so you can decide.
How to read your report
Your report groups findings by category with photos attached to each. Red flags mean walk away or budget a major repair. Yellow flags are negotiation leverage. Green items are confirmed good.