A pre-purchase used car inspection with OBD2 complements a mechanical checklist: you want a cold start, a highway segment, and a scan before and after the drive.

Read all modules your adapter exposes (often powertrain on generic tools), check for permanent vs pending codes, inspect readiness monitors for incomplete tests (could indicate recent clearing), and review freeze frame if MIL is on.

Live data during the test drive: engine temp rise, fuel trim behavior, and misfire counts. Unusual long-term trim swings may hint at hidden intake or fuel issues.

No pass/fail from codes alone—pair OBD2 findings with body/interior wear, service history, and an independent mechanic when stakes are high.