OK so lately I have been having a terrible misfire. It only seems to happen when I am sitting at a light or when I take my foot off the brake to ease up a little (I drive an auto). It doesn't jerk (misfire?), when I am driving. Because I have had the P0421 code for so long (at least 3yrs, but out of warranty), the guy I am taking it to believes that this is the cause of my problems. He's saying that the car can not properly get rid of the fumes from the engine which is why my car is misfiring. I called the dealer and they told me the same thing.

Now the shop I am thinking of taking my car to, has a pretty good reputation and I don't think they are trying to rip me off. I called the dealer and they also said that over time this code could start to cause misfires like this. The shop is quoting me $800 out the door. This includes labor, new front and rear engine mounts (they went out), and the cat.

My question to you guys is, do you think that the infamous P0421 problem could eventually cause me misfires?

LMK guys, I am scheduled for this morning

 

Buy the mounts and cat.
Spend half a day doing it all yourself, and save a bundle.
If your cat is clogged, it will indeed misfire.

The code doesn't make your car misfire.
If the code created a misfire condition, then most everyone with aftermarket header would be misfiring since most everyone with a header have P0421 light up their dash.
A code isn't a cause, it's a result.

 

Thanks for the response!

I have had this code for the past 3 years or so. Its just that now I can actually afford to pay to have it fixed now. I just never thought that a cat could be the cause of a misfire. 800 doesn't seem too bad considering the dealer quoted almost 1200 for just the cat and install. If I had a place to do it myself I definitely would.

 

My 02 Lancer ES just got the P0421 this morning. I haven't had any misfires or noticed it running any differently. Should i assume it's a sensor problem?

 

i won't assume it is a sensor problem, since there is another code for the Oxygen Sensor, atleast in my year, research yours

here are my experiences with this mysterious number.

the P0421 problem is something that I find really amusing, not sure if anyone else feels this way...

I had the P0421 problem started around Nov, when it is really cold in Canada. I've asked the mechanics on what this can do to my car, they said 'poor fuel mileage, less efficient engine' so I've been comparing my Winter Cost for driving on my Lancer, it came up to an avg of 10.5 km/L, not bad for a 5 year old car, especially when it was new, it was only doing about 11.x km/L during winter.

P0421 used to pop up every two weeks when the lancer is driven in the city, that frequency slowed down to once every month and a half when I switch to driving in the country side (daily driven)

and Since the snow melt, I haven't had a single pop up yet (that's since March). I am now back up to 13.x km/L because I no longer have to spend five min warming up the engine in the morning and evening.

so, would I consider changing my Catalytic converter? Maybe, if I can a few hundred bucks to spare, or if the light comes up and stays up, no matter how many times i reset it.

The funny thing is, the last time it came up, it shut it self off within the same drive.