The oxygen sensor, also known as the lambda sensor, is in the exhaust system and measures the oxygen level in the exhaust gases. This information is later used by the central computer of your Cadenza (ECU or PCM) to control the fuel injection and allow the engine to work efficiently without wasting fuel or reducing its efficiency.
The exhaust system may have 1 or 2 oxygen sensors. The main one is in the inlet of the catalytic converter, and it monitors the gases that come out of the engine. The second one (if your car has one) is in the catalytic converter outlet, and its purpose is to monitor its performance. It is important to remember that if the catalytic converter malfunctions, extremely pollutant gases will be released into the atmosphere. The oxygen sensor usually begins to fail after the car has driven from 55,000 to 90,000 miles (90,000 to 140,000 km), and that is when you should replace it. If it is working correctly, you do not have to replace it. Take into account that this is not an essential component with set maintenance periods, even if it helps your Cadenza work efficiently by reducing its emissions, and it also helps extend the engine lifespan. The oxygen sensor usually malfunctions when a lot of dirt has been accumulated due to the wrong fuel type or low-quality fuel usage. Most of the time you just need to clean it for it to go back to normal.
You will usually notice that the oxygen sensor is faulty when the idle speed is unstable, there is increased fuel consumption, and the check engine light comes on (you can see this light below).