Is this an upstream or downstream sensor?

The 234-4344 is a downstream sensor, mounted after the catalytic converter. Confirm the position on your vehicle before ordering, since upstream and downstream parts are not interchangeable.

How do I know it fits my car?

Check Denso's application lookup or your vehicle's OEM part number against 234-4344. Match engine, model year and sensor position, not just the brand.

Does it come with the connector?

Yes. It is a direct-fit sensor with a factory-style connector for the applications it is listed for, so no splicing is needed on those vehicles.

Do I need a special tool to install it?

An oxygen sensor socket makes removal and installation much easier, especially on a rusted or seized sensor. A standard wrench can work if there is clearance.

Will it fix a check-engine light?

Only if the stored code points to the downstream oxygen sensor circuit. Scan first; a P0420 catalyst code can have other causes, and a new sensor may not clear it.

How does it compare with a universal sensor?

A universal sensor needs its connector spliced onto your old wiring. This one plugs in directly on listed applications, which removes a common source of wiring faults.