bank 1 mean the bank of cylinder where the number 1 cylinder is and 4 cylinder engine only have 1 bank. there is upstream and downstream o2 sensor. upstream o2 sensor is the one before the cat and downstream is the one after the cat and ECU use it to monitor the cat's efficiency. if the o2 are dead, you'll get a different code.

 

Over the weekend I'll do the manual reset via the battery. Seeing how the error came on right after a quick stop at the Chevy dealer to see the classics on the showroom, I figure it was a random error.

We'll see!

 

It'll probably take 1 or 2 days to come back... I need some number of cool start and heat up for the Ecu confirm that the second O2 sensors need to be replaced.

In my case, that's was append. I change my 02 sensors and nothing came back. (I was thinking I do something wrong with Ecuflash the time cel ligth on.)

 

yea i reset it since saturday and hasnt came back!!

 

^Kewl! I'll see soon enough!

 

So yeah, yesterday the CEL just disappeared by itself...I was right!

 

dam mine came back today!!

but i think it might be my spark plugs
ima change them asap

 

^Ah, sorry man...btw, and thread came under the search keyword of "P421". I beginning to think there's a dealership TSB for it!

 

Acouple things to know about this P0421 warm-up catatyst efficiency below threshold (bank *) code.
Strictly speaking for Mitsubishi vehicle's that have not been modified.

- For people who don't have the time and money. If you don't notice a drivability problem with your car, it will be fine to drive. Only negatives in doing so would be the annoying check engine light. You can keep having the code erased from a local Schucks or Autozone and usually it will stay off for awhile before coming back on. Another negative would be the possibility of not passing your emission tests, if they are required by your state.

- The light will only come on after a certain amount of start cycles once you have the problem.

- Likely to be either a crack in your exhaust manifold or a worn catalytic converter.

- Unlikely to be your oxygen sensor(s) but you should still have them checked out.

 

I have the same issue with my car and I have emissions coming up in June and I am about to install my turbo kit in my car what should I do any suggetions? Will I still get the same code if I put on my turbo and manifold? or should I slap on the stock header for emissions?

 

i have a fooler that extends the post 02 sensor if anyone needs one, just pm me, i got it from rrm. it makes the code go away

 

How can you tell if you have a worn catalytic converter or if your oxygen sensor needs to be changed? If there is a crack in the exhaust manifold, I would have to remove that cover that says don't touch to see that right? (or is that not the exhaust manifold?) I still have stock header but after-market catback exhaust.

I have been riding on this code for maybe 2 months and the check engine light will randomly turn on and off for a couple days; my buddy told me that it's going to cost a couple hundred bucks to fix so I should just ignore it because it's not a big problem. But you know, you want your Lancer in tip-top shape any help towards getting this resolved is apprecated

(Mine said under bank 1 too.)

 

this is the best way to get rid of it with out having to resort going back to oem parts......do this....im doing it as well but mine is costing 5 bucks since im doing a custom one

 

What about when you take emissions test it just takes the light off it will not solve the problem and the code will still come up when you take the test?

 

all it does is trick the o2 sensor into thinking that its seeing what it should. so then it depends how they test the cars. if they look at the o2 sensors by obd2 then your all set. but if they put a 5 gas machine in your tailpipe, you may have issues.
will the code come up when you take the test? no, you get rid of the code by doing this
is this really that hard to understand?