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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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Default Re: code po421 2002 L300 v6

Mileage, maintenance done, parts replaced?

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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.

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Old 04-20-2014, 09:20 PM   #6
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Default Re: code po421 2002 L300 v6

[QUOTE=fdryer;1984465]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.

fdryer... I have this code on my '03, L300. I hoping it's the pre-cat O2 sensor like you had. What did you do to determine it was the pre-cat sensor?
thanks

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Old 04-21-2014, 12:54 AM   #7
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Default Re: code po421 2002 L300 v6

What error code? What's mileage?

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Old 04-22-2014, 07:22 PM   #8
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Default Re: code po421 2002 L300 v6

Quote:
Originally Posted by fdryer View Post
What error code? What's mileage?
P0421, the same you you said you had and replaced the pre-O2 sensor. I have the same car L300 03. I have 80K... thanks

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Old 04-22-2014, 07:48 PM   #9
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Default Re: code po421 2002 L300 v6

I don't recall what my error code was but it was for the pre-cat O2 sensors. Looking up error codes, I found P0135/P0155 for faulty heaters on both of my O2 sensors, not for the rear O2 sensors. I recall the heaters caused the fault codes and not the sensors themselves. P0421 is for the rear O2 sensor to indicate a faulty catalytic converter.

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Old 04-22-2014, 10:24 PM   #10
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Default Re: code po421 2002 L300 v6

OK, thanks... I have the P0421 but I hope it's not the cat. This week the check engine light is out and I did no turn it off. My son drives the car to and from school a short distance and I know it does not get fully warmed up. I'm sure this is not helping things.

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Old 04-22-2014, 11:12 PM   #11
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Default Re: code po421 2002 L300 v6

Short trip driving may be the reason for the random P0421 code as the catcon may not heat up to operating temperature where the O2 sensor may read correct oxygen levels. While it's just guessing, maybe a longer drive, 20 minutes or more will help the catcon and keep the error light off. If a longer drive or two results in no error codes then you might dodge the bullet about replacing things.

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Old 04-27-2014, 09:30 PM   #12
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Default Re: code po421 2002 L300 v6

Quote:
Originally Posted by fdryer View Post
Short trip driving may be the reason for the random P0421 code as the catcon may not heat up to operating temperature where the O2 sensor may read correct oxygen levels. While it's just guessing, maybe a longer drive, 20 minutes or more will help the catcon and keep the error light off. If a longer drive or two results in no error codes then you might dodge the bullet about replacing things.
I hope your right, like I said my son does drive it a short distance. The code come back on Friday after a week of being off. Going try and take it on a couple of long trips this week.

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Old 05-05-2014, 06:45 AM   #13
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Default Re: code po421 2002 L300 v6

This could be a 5 dollar fix. I had a P0420 a while ago. took out the bank 2 O2 sensor, installed the spark plug non fouler with the sensor back on and no more code. It eliminate all the codes that has to do with the cat. There's a youtube vid on it.

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