I have seen a few posts on here for this error code and am sorry for posting this again.

I took this to autozone today to get error code.

P0421

Warm up catalyst efficiency below threshold - cylinders 1-4

Has anyone else had this exact same read out? Where should i start first?

Thank you.

 

i got it right now lol been running with it on for a while its either the o2 sensor or the cat itself , o2 sensor is around $50 the cat weld in is bout $150 im just lazy but it does need to be fixed

 

I too have been running with this code for a while. Every now and then it comes on and i just clear it...

My question to those more knowledgeable than myself: Will this code hurt my car, or just the environment?

thanks.

 

Interesting - Turns out there was a recall for a parameter in the PCM being set incorrectly causing the SES light with that code.

http://www.mitsubishi-forums.com/t24...de-problem.htm
and
http://mitsubishiforum.com/forum/mit...-recall-32516/

Unfortunately i cannot find anything "official" from mitsu.

 

you might start to get crappy gas mileage after a while but mines been on for about a year and im still gettin 28-32mpg im just lazy and dont fix the problem lol

 

My foot is heavier than it should be, I rarely get good mileage in any car. I bet i would make a prius cry.

 

i hear ya, i was like that with my mustang but with gas prices goin crazy i do everything possible to get the best i can. might get better if i change the o2 sensor thats out lol but ive gotten 37mpg out of this car before so....hell i was gettin 28mpg with a blown head gasket for a couple mths.

 

37 MPG, that's impressive. My 02 was pulling the P0421 as well and I replaced the O2 sensor right in the from of the engine compartment (wanted to start with the easy one) and that cleared up the error.

Still getting other P codes now, but that's for another post.

 

I'm getting the same code and I have already changed out the one that's pre-cat. Where exactly is the one after the cat? I just don't wanna be underneath my car looking for it for about 10 minutes if I don't have to.

With situations like mine, it's a total time warp. 10 minutes turns into 2-3 hours a little too often.

When I first got my car about a year ago, I would get about 330-350 miles before I got the idiot light. Since it's averaged at 10.500 gallons filled at that point, that's about 32.50 MPG. Now it kind of struggles to get to 290 or 310 which equates to about 28.50 MPG. I'm pissed haha.

This is with a proper alignment, though tires are a bit grippier. :P

 

the second o2 sensor is under the car, you will see the cat and its right there. you can get the universal sensor and hard wire it or get the plug and play. if the plug and play the plug is under the carpet on passenger side at the floor pan. you will have to remove the shifter console to be able to pull the carpet back but its not that big a deal.

 

i didnt have to remove the console for mine just pulled the carpet up a little

 

Which one is easier in your honest opinion? While I don't mind splicing wires, I don't want to have to tear into my interior. Again. :P

 

The plug and play I think. I rather not have to soldier in the tight space. And its just the kick panel the step panelthen pull up the carpet

 

That doesn't seem so bad.