Bad O2 sensor?
 

So I have a 2000 Civic EX coupe, and a few months ago I had a check engine light, took it to advanced auto parts and got scan on it, and it was a bad oxygen sensor. So the guy reset the code so the light went away, well I'm planning on replacing it this weekend, but I want to verify it's still bad since the light hasn't come on since. One thing that's for sure is that it's never been replaced any my car has 129K miles on it, and the other thing I notice and it guzzles gas in the past year or so. And the final thing I notice about my car in the past few months is that it runs really choppy or idles very low about 500 rpms when at a stop light. So i'm pretty sure that it all points to a bad Cat or O2 sensor, but does anyone know what this could be? Thanks any help is appreciated.

Re: Bad O2 sensor?
 

How do you figure bad cat or O2 sensor with no CEL? When was the last full tuneup? Did you check timing?

Re: Bad O2 sensor?
 

He said it was scanned by parts store and it came up o2, but they just reset the cel and has not come again.

Dude, change it, I have 246k miles and just did mine with no check engine light.

I had noticed bad gas mileage black tail pipe exhaust on my back bumper.

I did the plugs first it got better, but then even with a CEL I did the o2 anyway.

Re: Bad O2 sensor?
 

I guess I'm not one for just replacing parts on hunches.

Re: Bad O2 sensor?
 

Just throw money at it, eventually youll replace the right part.

Re: Bad O2 sensor?
 

Guys he said the code came up originally, when they reset the code, it is just masking the problem, sometimes parts fail without codes, when the cel comes on typically it is when the part is way out of spec. MAP sensors and O2 sensors can get out of spec and not set off CEL's.

Re: Bad O2 sensor?
 

And the code never came back. He'd be best served by doing simple maintenance like a tune rather than replacing an O2 sensor that only threw a CEL once. Hell. It could be an exhaust leak.

Re: Bad O2 sensor?
 

I'd say full tune up and if gas mileage is still under par, then o2(s) need replacements. Maybe even a new CAT. Check Amazon for great deals.