[ReplicaR]

How do I determine which 02 Sensor needs to be changed. I know there are two of them, each one is around 220 dollars, which is definitely not cheap. I'd rather not replace both if I don't have to. Car gets a check engine light ever now and then, and goes off on it's own. I've checked the code, and it's the O2 Sensor code. Would taking it to dealer do me any good or would they just tell me to replace both?

Edit: BTW, the code was P0420.

 

[olegus]

P0420 can be either O2 sensor or bad catalytic. If you want to take chances, try to change a sensor that is after the cat, they(Denso) should be available for around $60, I believe.