Check Engine Light on....what's this code?

gapeachsp5

Member
:
03 Mazda 6s
I posted in the P5 section, but no one seems to know. My check engine light came on, so I went to Autozone and they found the code to be:P0031

I know it's an o2 sensor, but does anyone know which one? God I hope it's the first 'cuz it's cheaper.

Any help? I did a search, found one guy that said it was the first, but no one responded to his thread, so I don't know whether or not he was correct.
 
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