Tried searching for some info on this topic, but can't really find anything useful. Anyways, my driver's side cat is going down the tubes due these codes I've been getting for the last couple months: P1177 (O2 correction behind catalyst, B2 limit attained) and P0421 (Warm Up Catalyst Efficiency Below Threshold). So I've been toying with the idea to:

A.) Buy a used cat or the whole down-pipe section that includes the precat and postcat from a used parts place.

or

B.) Buy a new cat from Magnaflow, Flowmaster, etc and weld them in place.

What would you guys suggest doing? My biggest worry about A would be that the used cat may be clogged or on it's way out the door already. I'm also unsure how I would go about installing the aftermarket cats, relocating the sensor bungs, and what to do with the precat.

My car is kinda high in mileage so I don't wanna throw more money than necessary at it. I would like some MPGs back as well, haha.

Any help or advice is greatly appreciated!

 

There's a possibility that your B2 secondary O2 sensor is failing. Since they're next to each other on the pipes, you could swap the two rear O2s in the exhaust bungs, leaving them plugged in, and see what happens after clearing the codes. This way the driver side O2 is measuring the efficiency of the passenger side cat, and vice versa. If you start seeing codes for the passenger side cat having trouble, you'll know the driver's cat is bad. If the codes continue to indicate a bad driver side cat, your issues are in the B2S2 oxygen sensor.

 

I'm pretty sure the O2 sensor is okay since I replaced the secondary O2 sensors for both sides about a month ago. But I'll switch them like you said just to make sure that my cat is really failing.

If the cat is bad, what route would you suggest going?

Thanks

 

Chances are then that the sensors are ok. Make sure they're tight too though. If you have to replace the cat, I'd find one from a car being parted out.

 

I'll check that. I guess I need to add a cat to the list of things my car needs! Ugh. Thanks for the help.