When I first got my car, I used a Bosch O2 sensor, and it passed emissions . I recently failed emissions, and broke down and bought a factory sensor $98. Between tests I had put on a Thorley header. Comparing both O2 sensors side by side, I see why I failed. The Bosch is so short at the tip, that it wasn't even in the exhaust stream. The Toyota sensor is much longer at the tip, and was designed to work with the header, that was, at the time an OEM accessory part. This was an expensive mistake trying to save a few bucks. Live and learn.