Question about 2004 Mitsubishi Endeavor

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Serveral weeks ago my service engine light came on so I took my Endeavor to the dealer and they said it was randomly misfiring so I should replace the spark plugs. Since I was at 97,000 miles that seemed reasonable. Since then the light has come back on twice with the P0421 code. The weather was cooler yesterday and the light went back out. What should I do now?

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The signal concerns your catalytic converter. Generally either the catalytic converter is at fault ( ouch!) or the oxygen (lambda) sensor is reporting too much oxygen i.e. the car is running lean. Keep running the car but at some point maybe have the car exhaust checked for nitrous oxide content. At the same time time, once you have run the plugs for a while, take one out and check it it for condition: light grey is perfect, black indicates too rich and glazed indicates way too hot. If glazed and the nitrous oxide content of the exhaust is high then the EGR valve and ports should be stripped and cleaned.

Posted on May 11, 2010

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This code indicates that the catalytic converter is not working well enough. The dealer installed the plugs in hope that maybe the engine would run cleaner and not load the cat so much with new plugs installed. Bottom line, you need a new catalytic converter, but be sitting down when they give you the price. I would see if I could get warranty on this as it is mandatory in some areas.

Posted on May 11, 2010

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