I'm trying to fix up a 2005 Civic DX that's new to me, 90k miles. Initially it wouldn't pass SMOG due to a P0139 problem (O2 sensor slow response, Bank 1-Sensor 2). There's only BOSCH sensors around here, so I use it for the immediate fix on the downstream O2. Clear the code and it drives fine. After about 40 miles, it's now throwing P0420. I wanted to get some 2nd opinions as that's what the Internet is good for. I know it could be the cat, the upstream O2 sensor, or maybe I got a bad/wrong downstream sensor (for the wrong engine ID - I didn't know they were that specific until today)?

• After researching, I don't think its the cat as it drives fine (to me anyway), plus the SMOG test had all acceptable values in the actual measurements.
• I'm up for replacing the upstream O2 sensor, but there's several part numbers on rockauto for denso.

Anyway, just wanted to get some thoughts before I throw more (expensive) parts at the problem. Are civic's picky about their O2 Sensor for each submodel? I'm thinking about getting an O2 sensor for the correct engine first... *sigh*

EDIT: I just did a VIN lookup, and it says it's a Civic EX (2dr coup, AT), which matches the BOSCH sensor I bought. So I'm pretty sure the O2 sensor is right at this point, just a Bosch.

Cheers!

 

Don't use BOSCH. Use OEM Denso or NTK.