P0421
 

2000 mazda 626 4cyc.

Could some1 help me figure out whats wrong. Where 2 check or replace first. My code i keep getting is P0421, warm up catalyst below threshold(bank 1).. Thats all it says, i have no idea what that means. Please help.
Brian

I have an 01 Mazda 626 LX and I pulled that same code. I was told it is usually the spark plugs, the O2 sensor, or the catalytic converter that is not working properly. The majority of the time its the converter that is messed up, but in a few cases like mine it isn't. I replaced my converter since the spark plugs were new and I still have the same code. The only reason I didn't change the O2 sensor yet was because all of the mechanics and forums I looked at kept saying that a bad O2 sensor would cause another code with the P0421. My suggestion is start small. Check the spark plugs, then the O2 sensor, then lastly the converter. They are approximately $4, $65, $150 respectively.

Let me know how your case turns out.