Mehfuz has written a NativeScript plugin to interact with ODBII sensors. We will publish a proper post in the NativeScript.org blog but, in a nutshell, it uses the BLE APIs on an Android device to interact with an ODBII sensor like this one:
The ODB II Bluetooth adaptor is for Android only because the Bluetooth APIs on iOS are restricted to MFi devices and there are very few of those – most ODB II iOS devices use WiFi instead.
NativeScript is a natural technology for this type of applications. I’ll add a link to the proper NativeScript.org post when it goes live.