How do I know the 234-5049 fits my car?

Check the part number against your vehicle's engine and model-year application list before ordering. DENSO builds several air/fuel sensors that look alike but differ in connector and calibration.

Is this an oxygen sensor or an air/fuel ratio sensor?

It is a wideband air/fuel ratio sensor, which gives the engine computer a broader mixture reading than a narrowband oxygen sensor. They are not interchangeable.

Do I need a special socket to install it?

Yes, an oxygen sensor socket with a slot for the wire makes removal and installation much easier. The sensor itself does not include tools.

Should I replace both sensors at once?

Replace only the sensor the codes point to, and fix any vacuum or fuel faults first. Replacing a good sensor will not cure a mixture problem caused elsewhere.

The sensor with its factory-style connector. Anti-seize and mounting hardware are generally not included, so check whether your application needs them.