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Old 06-18-2012, 02:59 PM   #1
solidbass
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Default code po421 2002 L300 v6

so about a week ago my cars check engine light came on with the code po421; which has something to do with the cat not running efficiently enough because it's too cold or something. anyways, this happened about 2 months after changing my thermostat. is it possible that the thermostat/extension tube is leaking coolant onto the cat causing the problem?

would anyone recommend Bar's Leaks Radiator Stop Leak as a fix or does that stuff gum everything up after awhile?

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Old 05-26-2013, 06:22 AM   #2
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Idea Re: code po421 2002 L300 v6

I just got this code po421 350 miles after I replaced bank 1 o2 sensors, thermostat&T sensor,and replaced spark plugs. auto zone scan pull this po 421 bad converter,or vacuum leak,or oil leaking into valve guildes to pistons. I;ll bet its the convertor because when I kick it in the ass to pass it stalling out ,and seems exhaust is louder under hood next to fire wall. other words not flowing like it should.

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Old 05-26-2013, 12:27 PM   #3
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2003 L-Series 3.0L Sedan
Default Re: code po421 2002 L300 v6

Mileage, maintenance done, parts replaced?

...
*The CPS is the heart of the entire EFI system. No cps = dead EFI system*
*There's more to a/c than just a few cans of refrigerant*
*There's more to brakes than just replacing parts*

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Old 06-02-2013, 03:35 PM   #4
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Default Re: code po421 2002 L300 v6

it has 140,000 on it. ive had the front upstream o2 sensor changed as well as the back downstream 02 sensor. i actually put seafoam in the car and it shut the code off for a few months...now its back on with a another code po442. im gonna throw some more seafoam injector cleaner and hope for the best.

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Old 06-02-2013, 05:15 PM   #5
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Default Re: code po421 2002 L300 v6

Well, from your first post, leaking coolant on the exterior of the exhaust system wouldn't cause the P0421 error code as it points to the catcon either worn out or the O2 sensor. Mileage has a bearing on both. I was forced to replace a pre-cat O2 sensor after only 75k miles () due to the heater failing. The error light intermittently turning on and off won't go well if NYS inspection sees this or sees any recent pending errors. Replacing the O2 sensors is only one solution and correct if the error codes don't come back otherwise the catcons are next in consideration. The P0442 error is for an evaporative system leak - either the gas cap seal or other issue is now the new problem.

If this DTC P0442 Evaporative Emission (EVAP) System Small Leak Detected is a gas cap issue, examine the cap gasket and filler neck. A brittle gasket, dry rot and cracking will allow the error as a vacuum leak occurs here. A gasket in undamaged condition may simply need cleaning and a little silicone spray to rejuvenate it or outright replacement. The filler neck should be smooth and clean of any stuck debris to allow a good seal when the gas cap is put on.

...
*The CPS is the heart of the entire EFI system. No cps = dead EFI system*
*There's more to a/c than just a few cans of refrigerant*
*There's more to brakes than just replacing parts*

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