Cel - P0421 Bank 1 Cat Efficiency Below Limit

[michaeltroysmith]

Had my CEL come on once again.... seems to be common occurence. Well this time I went to Mazda to run a diagnostic. Here are the results so that everyone knows. P0421 code came up and when cross referenced with Mazda's many service bulletins, it comes up that the Right Rear O2 sensor should be replaced due to over-sensitivity. Part number KJY2-18-861. If you are in Canada this part retails for $136.27 and there is a labour factor of 0.8 of an hour. The service manager told me that this is a common occurence and indicates no problem with the engine or catalytic, just a "over-sensitive" sensor installed at factory. After surfing the internet for comparative prices.... I am going to stick with the dealer, as I have seen everything from $100 USD to $240 USD. So $137 Canadian is a good enough deal and since they have the tools I will get them to change the part when I have the 96000km (60000 mile) service done.

[mazdatech]

i have seen this problem and the person put an o2 in it like the tsb said but it ended up being the precat was coming apart i replaced the pre cat and fixed the promblem(the dead giveaway was the new o2 sensor that i unsrewed was speckled with peices of whiite stuff ...(pieces of the cat) but it could have been a combination of the two that fixed the problem.