p0420 Catalyst System Low Efficiency
 

Threw the code today. The rear 02 is brand new so I know its not that. idle's very smooth and runs great so I'm kinda at a loss here. Could it just be the cat going bad? Anyone else had this one come up?

If your catalytic converter isn't doing its job then it could throw that code even if the car is running fine. If it was something else then I would imagine other codes being present as well. Also was the O2 sensor an OEM replacement or aftermarket?

What I would do at work is I would scan front and rear o2 sensors voltages. If the cat was working you would see the front o2 toggling high and low voltage and the rear o2 would be fairly smooth. If that cat was bad the. You would find both sensors toggling high and low. However. Typically it's just a bad cat. Very rarely have I seen it be something else.

02 sensor was a new factory replacement. I feel like I would be noticing SOMETHING else is their was a problem other then the cat going bad. I havent been able to check voltages on the 02 sensors yet but I do know what to look for, I'm an electronic tech myself and wired up code eliminators on the mustang. I think I can pretty well rule out most of the stuff on sleepy's list. The cat its self just seems like to best to start at least. Probably have to go with a piece of test pipe in place and wire in a code eliminator for now. catalytic converters are to damn expensive.

If it's not plugged, do t worry about replacing it with strait pipe.

I'm leaning more towards the flowmaster. It will just be a swap into the factory pipe and I'll have him cut out the resonator as well. Suitable replacements?
http://www.ebay.com/itm/Flowmaster-2...bed8c9&vxp=mtr
http://www.ebay.com/itm/2-Thunderbol...c877bb&vxp=mtr
Any reason the cheap one wont cut it? at least for a temporary proper solution. its supposed to be "high flow"
found this one to http://www.summitracing.com/parts/cto-6904/overview/

any input? I believe alero's meet California emissions so will a cat that is otherwise legal but doesnt meet California emission through a code?

Is this the Alero you picked up by me?

If it has the AIR tubes on it, it has the Cali emissions, if it doesn't, it just has regular emissions