I am confused about what brand of oxygen sensor to buy for my 1998 Honda Accord, LX, 4 cylinder engine. My mechanic said check engine code is PO420 and it is the upstream sensor. He also said he wanted $350 to replace it. I found a Denso 234-4620 for $60 on Amazon.com. What is really confusing is there are sensors for CA emmission engines which are about $100 more expensive. I looked on under my hood on the white emmission sticker to see if I have the CA emission system. It didn't specifically say one way or another. I live in LV, NV and this accord could have come from CA. I know my engine is the L4 (2.3L) and think the ID: is F23A1, so what is up with this F23A5 I keep seeing? Thanks.

Buy an exact replacement--you may want to remove the old sensor first and get the part no. off it. Here's how to do the job yourself:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563.html#post223376

I am confused about what brand of oxygen sensor to buy for my 1998 Honda Accord, LX, 4 cylinder engine. My mechanic said check engine code is PO420 and it is the upstream sensor. He also said he wanted $350 to replace it. I found a Denso 234-4620 for $60 on Amazon.com. What is really confusing is there are sensors for CA emmission engines which are about $100 more expensive. I looked on under my hood on the white emmission sticker to see if I have the CA emmision system. It didn't specifically say one way or another. I live in LV, NV and this accord could have come from CA. I know my engine is the L4 (2.3L) and think the ID: is F23A1, so what is up with this F23A5 I keep seeing? Thanks.

DTC P0420 is Catalyst efficiency below threshold

Its amazing that your mechanic wants to throw an oxygen sensors at your car to fix a dying catalytic converter, he must be one heck of a mechanic and I hope you have deep pockets.

You're going to want to use Genuine Honda replacement when you do replace anything because otherwise you'll be paying & replacing again shortly.