What's the difference between a bidirectional scan tool and a regular OBD2 code reader?

A regular code reader only pulls and clears diagnostic trouble codes and shows live data. A bidirectional tool can send commands back to the vehicle—cycling actuators, running active component tests, performing ABS brake bleeds, and completing service resets like EPB, oil, and TPMS. Several listings in this category (such as basic code readers) are not truly bidirectional despite appearing in adjacent searches, so confirm the active-test feature before buying.