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I have 2004 mitsubishi lancer. Service engine soon light is on. It gave P0421 error message. I changed O2 sensor1 and catalytic convertor with manifold but the problem did not solve. What will I do?

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According to my quick bit of research you should contact the dealer. it is a recall. a couple of people posted online that was what happened to them and it was repaired for free. also, i 'm reading that the mileage does not effect this recall in particular. no harm, no foul to make a phone call.

Posted on Sep 24, 2008


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P0421 CODES AND C1201

C1201 error code means that you have some problem in engine control system.

Possible causes for P0421 error
  • Warm Up Three Way Catalytic converter deterioration or malfunction
  • Exhaust system leaks
  • Loose front or rear HO2Ss
  • Faulty front heater O2 sensor
  • O2 sensors harness is open or shorted
  • O2 sensors poor electrical connection

The P0421 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem.

Apr 24, 2014 | Toyota Avensis Cars & Trucks

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2003 mitsubishi lancer will not pass smog code P0421 comes up what is this.

code P0421 may mean that one or more of the following has happened:
  • The catalytic converter is no longer functioning properly
  • An oxygen sensor is not reading (functioning) properly
  • A sparkplug is fouled up
Possible Solutions

Feb 27, 2011 | 2003 Mitsubishi Lancer

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Codes for engine 2003 mits lancer the code is P0421 warm up catalyst efficieny low bank one. what does this mean. and how do i fix it .thanks chad


Aug 02, 2010 | 2003 Mitsubishi Lancer

1 Answer

Mitsubishi pinin fault code P0421

yes this is your catalytic convertor is clogged you have to change before is damages ur o2 sensors

Feb 12, 2010 | 2001 Mitsubishi Montero

2 Answers

Engine light on- PO421 Catalyst system bank 1

taken from:

Code P0421- Call Mitsu before you do anything! I called my nearest dealership today and for those who dont know, if your check engine light is on and its showing fault code P0421 this may be from a factory recall on the warm-up converter and a PCM reflash. MILEAGE OF THE CAR DOES NOT EFFECT THIS RECALL. Anyone whos had problem with a dealership not doing the repairs because of mileage needs to contact another dealer or the owner of the dealership. This is what the service manager told me today so though I'd share. Getting mine fixed tomorrow at 10am, I cant wait.

For more information about this code Google "Fault Code P0421" You'll get tons of information Last edited by Swankzer; Jun 2, 2008 at 12:31 PM.

Sep 30, 2009 | 2002 Mitsubishi Lancer

1 Answer

2003 Lancer the service engine soon light keeps coming on, have changed out both O2 sensors and the gas cap, the code is P0421. The light comes on about 15 miles after filling up with gas

I can see that you've done the right things, but something is still amiss... Mitsubishi says

A code P0421 may mean that one or more of the following has happened:
  • The catalytic converter is no longer functioning properly
  • An oxygen sensor is not reading (functioning) properly
  • A sparkplug is fouled
Measure the voltage at the oxygen sensor on Bank 1 (the rear sensor, or the sensor after the converter). In fact, it would be a good idea to test each oxygen O2 sensor while you're at it.

One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.

Sep 23, 2009 | 2003 Mitsubishi Lancer

1 Answer

Service engine soon light is on

That is a heated o2 sensor problem o2 sensor should be replaced about every 80,000-100,00 miles.

Aug 14, 2009 | 2003 Mitsubishi Lancer

3 Answers

Spinning My Wheels!! ---- P0421 Code Mitsubishi Galant

I have the same vehicle, same code P0421, changed the BOTH O2 sensors and the check engine light was still on, took it to my fathers garage and checked the Catalytic Converter, and it was ok later I found out that P0421 means that the vehicle doesn't have the proper mixture of gas and air (running richer) so I changed the MAX air flow sensor and wala the code went away.

Mar 30, 2009 | 2003 Mitsubishi Galant

1 Answer

My service engine soon light is on on my 2004 Mitsubishi Lancer.

You can't guess with this vehicle take it to Auto-Zone they will check the code for free and get back to me. Good Luck

Nov 29, 2008 | 2003 Mitsubishi Lancer

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