I wrote this article to save you a few hours of research and some money.
If you happen to have a 2006 Hyundai Sonata, it seems that around 100.000 miles (160.930 km) you need to replace the oxygen sensors. If you don’t do so your catalytic converter will go bad; that is much more expensive.
This is not rocket science, however it requires some basic skills.
You need Oxygen sensor(s), 7/8 inch (22mm) oxygen sensor socket (with a groove in the middle for the cable) and ratchet for it (a long one since it can be hard unscrewing the old ones), anti-seize, gloves, and patience.
I suggest go with Japanese parts.
Front: Denseo part number 234-4433, rear: Denseo part number 234-4439.
On the 4 cylinder, 2.4L engines you have two. One before the catalytic converter (front) and one after (rear). I don’t know how it is on the 6 cylinder ones.
The sensors are located somewhere under the windshield wipers. If you stand in front of the car looking at the car the front one is on the left side and the rear one on the right.
The front one has a ring on it and the sensor itself is a tiny bit thicker. Don’t mix them up!
The sensor replacement has to be done with a cool engine; it is easier to unscrew the old one(s) and you also won’t burn yourself. Before you insert the new ones put anti-seize only on the screw part of them.
If you are here you should know already how to connect a OBDII scanner to your car and read values with your phone or dedicated tool. I use Panlong WiFi OBD2 tool and FourStroke app, which is free; however if you want to read O₂ levels then you’ll need the premium version ($3,99). Mostly you need to check your O₂ sensors voltage. This should jump between 0.1V and 0.9V, more about them here. If you see their value is moving between these two values then your job was done, all should be good.
Warning! Do the work at your own risk! If you are not sure what to do and lack basic car repair competence, don’t do it
PS: After changing the O₂ sensors and cleaning the Mass Airflow Sensor my gas consumption went down about 5%.