P0421 code on p5 help...

I have a few questions about my cel light which came on a while back. I started repairing the 'issues' to rid myself of this light so I can get the mazdaratti inspected.

First, I had to replace the 'after cat' o2 sensor. Once that was replaced, there was another cel... That code said it was a vacuum leak or a fuel injector problem (P0171?). Anyway, I discovered that my air intake hose was cracked almost in half. After replacing the hose, I now have another code...the P0421.

My question is how do I know which cat to replace? I see there are two on my car; one is $300 and the other is $80... Since this thing has 120,000 miles on it I only want to spend what I have to. Any help is greatly appreciated.

it will usually be the one that is on the bottom of the exhaust manifold (300) one i believe, or you can do a o2 simulator for 5 dollars Go to auto zone and buy a spark plug non fouler believe it is 42002 the 18mm one, and drill it to 1/2 inch , then unplug your rear o2, put in the non fouler and then the o2 sensor, dont forget to reset the ecu. And youll never see that 0421 ever again.

youll need a drill , 1/2 bit, wd40 for getting bolts off, 10 mm, 21 mm and five minutes

I did the non fouler trick on my car, got rid of a p0420 code...similar to your p0421...The cat doesn't have busted off chunks...you can still see through all the substrate, but I didnt feel like putting in either a new o2 sensor or cat, or both.

So far it's been over 10,000 miles, and no 02 sensor code...although I wonder if a new front 02 sensor would help with mpg.

Oh yeah...it was a rust belt car, so getting the damn rear 02 sensor off took waaaaay longer than 5 minutes.

lilpoindexter said:

Oh yeah...it was a rust belt car, so getting the damn rear 02 sensor off took waaaaay longer than 5 minutes.

Click to expand...

thats where the wd40 comes in handy