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P0421 Yes i searched..

  #1  
Old 07-10-2009, 05:47 AM
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Default P0421 Yes i searched..

So my car is an 03 lancer, has had a p0421 code for a while. I replaced the cat and both o2 sensors and the problem still isnt fixed. Any ideads?
 
  #2  
Old 07-10-2009, 08:43 AM
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How many sensors on your car? I thought it was 3 not 2 sensors
 
  #3  
Old 07-13-2009, 04:51 PM
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the ONLY thing that will cause that is a failed cat.

NOT failed o2 sensors.
 
  #4  
Old 07-14-2009, 09:07 AM
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He never answered me back it means he solved the problem.

He said he replaced the Cat Back but still has a problem he probably replaced all 02 sensor.
 
  #5  
Old 07-19-2009, 07:39 AM
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naw it hasnt been fixed. Im still pondering of what it could be.. I tested the tps sensor, checked the spark plugs countless things. Any other suggestions. One thing i noticed which is VERY odd is the downstream o2 sensor is before the cat and not after it. I find that very odd. How is it supposted see if the cat is working or not?
 
  #6  
Old 07-20-2009, 08:26 AM
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This code that keeps coming back could be the following.
Aftermarket Cat installed. (These cars need originals)
heated O2s wiring problem check wiring to PCM / ECM
if all checks out good you could well have a bad PCM / ECM
Your cat is up on the exhaust manifold right under the first O2s
if i remember correctly.
 
  #7  
Old 07-20-2009, 07:03 PM
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you replaced the wrong cat.

the one thats monitored is in the exhaust manifold
 
  #8  
Old 07-20-2009, 07:11 PM
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Originally Posted by Manybrews View Post
you replaced the wrong cat.

the one thats monitored is in the exhaust manifold
X2 on this.
 
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