All 2003 Sonatas use four wire oxygen sensors.  If someone is selling
2-wire sensors for a 2003 Sonata, you should take that as an
indication that you should stay away.

Additionally, there was a change in ECM logic and oxygen sensor design
for the V6 partway through the 2003 production run.  Even if you
purchased a four wire sensor, there’s no guarantee it’s correct for
your car.

Furthermore, many Hyundai oxygen sensors have a bias voltage.  I’ve
heard of problems using aftermarket oxygen sensors