Good evening,

Can anybody tell me if i should be worry about my 2000 mazda millenia. The check engine light came on, it shows P0421 warm up catalyst , below threshold.
I had the sensor for the catalyst changed a while ago. I really dont want to spend a lot of money.
Does anybody had the same problem? if so, how much did you spend on fixing the problem?

Hope i can get a quick response

Miguel Rivadeneira

 

p0421 is 2.3 motor, you are looking at changing out the pre cat. also known as the exhaust manifold. mazda has dropped the price on this down to 416.00. that's about 1/3 of what it used to be. not a bad job, i just did this a couple of months ago, takes about 3 hours. i would not even think about doing it unless you have a lift and air tools. you will need to pull a lot of stuff off, like the exhaust system.

 

If it is not affecting the driveability of your car just erase it for now! Its more and likely an over sensitive O2 sensor! Run a search within this forum for a code p0421, and it will tell you more of what you want to know!

 

nope, it's your pre cat. if it was the sensor, since it was recently changed, it wouldnt throw a ce lite again. i just went thru this. ce lite came on, i would erase it. it would always come back, and the interval got shorter and shorter. it was cycling about every week, and i changed out the sensors, and reset. about a week later, back on. always 0421(rear bank). changed the pre-cat, and it has been off now for at least 3 months. the rear pre-cat is only 416.00 from mazda, then you gotta get some gaskets. took me about 3 hours, but i had a lift and air tools. we had to drop the exhaust, too. pretty straightforward, but looking back, i would NEVER do it unless i have a lift. you will be surprised at the gain in performance.