Engine code PO421
 

My 2002 Pro5 Check engine light has come on and the car has a definite loss of power.
Went to Autozone and they came up with Engine code PO421 -"warm up catalyst below threshold"
He then tried to sell me a new O2 sensor for $250.
Any help or ideas?
Thanks, Pat

It could be the same code I just had but I am not sure. Mazda hase a 120,000km 8yr or is it a 128,000km 8yr emissions warranty. My cat is being replaced because the code I just got saying the second O2 sensor was getting a inconsistent reading. Go check out the dealer first and don’t let them tell you they will still charge you for pulling the code. I had a huge fight with my dealer about this because I feel if the code is from a warranty issue I should not have to pay….and I won!!!!!

warranty
 

yo, just going through the forum to try and solve my problem. my O2 sensor went bad and wether i change the one after or before the catalyc converter, they are about $200 each. so my question to your thread is, you are saying that the emission warranty is for 8 years - 120, 000 km but all my factory warranties experied already, can i still get this one? i really dont want to spend all that money on a tiny ass sensor. please get back to me, thanks

P0421 simply means the first O2 is too close the reading of the second O2. Changing the sensor would be like shooting the 6 o'clock news guy when he is just reporting.

You need a new convertor. The parts and labor are covered for 8 yrs and 80,000 miles.

Exactly. This is a government regulation relating to emissions standards. ALL cars sold in the US are required to meet the 8 yr, 80,000 mi requirement.