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Check Enginer Light is Never Ending!!

Old 12-20-2010, 01:41 AM
Junior Member
Thread Starter
Join Date: Dec 2010
Posts: 1
Unhappy Check Enginer Light is Never Ending!!

My car is 2003 Mitsubishi Lancer ES, and engine service light is on, code is P0421. My car has approx 35,xxx miles on it. I get oil changes every 3k miles or 6 months as I obviously do not drive a lot. When the light first came on, I changed the O2 sensor. I believe it was the top one at approx $150.00 including parts and labor. The check engine light went on again, same coding. So I changed the lower O2 sensor for another $150.00 including parts and labor. I've read many of posts on here and am looking for some advice.

Also, when I had a friend use the check engine light machine a 0.525 for heat or something had shown up. Not sure if this of further help.

I highly doubt that at 35xxx miles my catalytic converter would be shot when other posts are saying their cars are over 100k miles. Any thoughts or opinions here?

I could really use assistance here as I don't have $1k for a new cat converter.
Old 12-20-2010, 06:39 PM
Junior Member
Join Date: Dec 2010
Posts: 5

I highly doubt your catalatic converter has gone bad with only 35,000 miles on it but depending on what kinda driving you do in town or highway but if you do alot of in town driving where your car sits alot idling your catalatic converter could plug up and go bad. I myself have never seen the code P0421, were did you have the service engine soon light tested and whats it telling you and myself ive never heard anything about the heat thing your dealing with. Sorry trying to help as best as I can
Old 12-21-2010, 08:35 AM
Join Date: Jan 2009
Location: Atlanta, GA
Posts: 48

I'd lay a serious bet that it's your front cat (since you've replaced the O2's), the one in the exhaust manifold (the expensive one). The good news MIGHT BE that you can take it in to a dealer under a cloudy (hard to figure out) recall. Emission components are warranted for 8 years/80,000 miles, so you would seem to have a pretty good argument to be covered. This issue is hitting a lot of Lancer owners from those years, me included. I believe there is a recall on the computer programming on these cars that is supposedly responsible for running the fuel mixture incorrectly, resulting in premature cat failure. PCM update I believe. I fell outside of the recall due to time and miles to get the cat paid for, but the front cat absolutely fixed my issue and many on another forum agree.
Get it in to the dealer as soon as possible since you are well within mileage, but are pushing the limits on age of the car. Be pushy to the service goober that greets you, tell them you KNOW it's covered. Some of those guys get dodgy with warranty work. If they turn you away, find another dealer.
I'm also going to send you some info private message, so check your inbox.

Last edited by Fe2O3; 12-21-2010 at 03:29 PM.
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