OBD-II (On-Board Diagnostics)

OBD-II is a standardized diagnostic system built into all US vehicles since 1996. It monitors engine performance, emissions, and other components. When a problem is detected, it stores a diagnostic trouble code (DTC) and may trigger the check engine light.

OBD-II scanning is a standard part of used vehicle inspection. It reveals stored fault codes that may indicate current or past issues, even when the check engine light is off. Dealers should include an OBD scan in every acquisition inspection to catch issues before they become recon surprises or post-sale problems.