If you have an Android phone, a $10–15 Bluetooth OBD2 adapter, and some patience to learn the menus, HHOBD Advanced is a solid free tool. For the price (free), it outperforms many paid apps in raw data access. Just don’t expect polish.
Go into Settings → Adapter Type → Choose "Bluetooth" or "BLE" depending on your device. And check the app’s compatibility list for your car model first. hhobd advanced app
Title: Surprisingly capable for a free app – great for hobbyists If you have an Android phone, a $10–15