Hi everyone. New to the forums.

I had autozone do a computer code check and it came up P0420. The definition explanation is "catalyst efficiency monitor malfunction - bank 1". Does anyone have a sense of what might be causing this? Thanks.

Mazda Protege '99 Standard

 

autozone couldn't tell you? You can do two things, call a mazda dealerand ask mechanic or the parts guy( have had good info from both in the past) or in the middle of menu bar , click the search and type in the P0420 and you'll be shown past posts about the topic. Good hunting!!

 

possible 02 sensor

 

i was thinking the 02 sensor also. which one?

 

its not the o2 sensor if it was it would say the cat efficancy really on every cat there are 2 o2 sensors one before the cat and one after the first one will read the fuel being left in the exhaust pipe and the second one will read the fuel again now if there is a change between the 2 sensors it means the cat is doing its job but when both sensors read the same thing it means the cat is not working. what you can do is take it to an exahust shop and have them check out the cat before you go ahead and replace it right away cause i have the exact same problem and ill tell you this your looking at least $400 to replace it thats the cheapest i have found. and no you can't put a universal one on because mazda designed the cat a certain way so you have to buy there's a universal one will not fit.

 

Does anyone know the oem and p/n for the 02 sensor for this vehicle?