Konwei KDIAG is the cheapest Bi-Directional scanner I have ever found so far. It might not have the best vehicle & function coverage for advanced functionality but it does already work with 30+ brands and even offers bi-directional tests for not only cheaper price for adapter, but also without any yearly payments. Updates are free for KDIAG.
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Konwei KDIAG is not the best bi-directional scanner but given it’s low price and free updates, it is even cheaper than most engine code readers or ELM327 adapters.
And it comes with features they do not have, like full scan or bi-directional testing.