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Old 02-21-2013, 01:03 PM   #1
south42
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2004 L-Series 3.0L Sedan
Default 2004 l300 - p0421

Just picked up this vehicle, 82500 miles. Put new plugs in, new air and cabin filters. The vehicle has thrown this code (P0421) twice. My understanding is that the bank 1 (firewall side) pre-cat converter is bad, or the O2 sensor downstream of the bank 1 pre-cat is going bad.

Two questions...

Is my understanding correct?

Is there an easy way to determine which (02 sensor or pre-cat) part is needing replaced?

Thanks.

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Old 02-21-2013, 01:48 PM   #2
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Default Re: 2004 l300 - p0421

P0421 Warm Up Catalyst Efficiency Below Threshold Bank 1

Four O2 sensors, a pair for each exhaust bank, the main pair is before the two pre-cats while the remaining pair is behind the two pre-cats. The main sensors are the important ones that tell the ecm when to regulate the fuel/air mixtures for emissions control. The ones after the pre-cats are for measuring catcon efficiency and tend to output a steady millivolt signal when the catcons at operating temperatures. Sensors aren't outputting until exhaust temps exceed 600F.

Factors determining a failed O2 sensor; wiring damage, loose connections, catcon worn out/damaged, excessively rich fuel mixtures, lean fuel mixtures, etc.. Experience and equipment can help narrow down either the pre-cat or O2 sensor fault. First thing to do is to inspect the O2 sensor and wiring as a visual can go a long way to finding the easy stuff before going further. Measuring output requires a multimeter and connections to the O2 sensor and observing output from cold start up to normal engine operating temps. Comparing outputs from the other sensor is one way while knowing the normal output is another. 500-800 millivolts (0.5-0.8v) is normal. This assumes the engine isn't running excessively rich or lean and the pre-cat isn't burned/worn out. Testing the sensor off the engine requires a propane torch to heat the sensor above 600F for any output to be seen on a multimeter capable of measuring less than 1-volt dc.

Rockauto, Autozone, Advance Auto, etc., all sell O2 sensors. The post cat sensor is the one you're looking for unless its the pre-cat.

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Old 03-05-2013, 03:54 PM   #3
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Default Re: 2004 l300 - p0421

Pulled the O2 Sensor and cleaned it with a little Muzzleloader bore cleaner and a shop rag. Put it back in and havent had the code again. Did go ahead an ordered a new O2 sensor, and will install it when it gets here.

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Old 03-05-2013, 07:14 PM   #4
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Default Re: 2004 l300 - p0421

"Four O2 sensors, a pair for each exhaust bank, the main pair is before the two pre-cats"
He has a 4 cyl.

Mike

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Old 03-05-2013, 08:45 PM   #5
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Default Re: 2004 l300 - p0421

Yes, he does but the title says '2004 l300'......

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Old 03-06-2013, 10:38 AM   #6
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Default Re: 2004 l300 - p0421

its a 6 cyl...and it threw the code again last night...the new O2 sensor will go in this weekend.

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Old 03-06-2013, 10:47 AM   #7
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Default Re: 2004 l300 - p0421

Quote:
Originally Posted by fdryer View Post
Yes, he does but the title says '2004 l300'......
That model number and engine size would've confused me as well. I remembered spotting this oddity in Rockauto.com for the '04 models. Here's a quote from Wikipedia about the model name change for that year:

"2004: Anti-lock brakes and traction control were standard again, the automatic air conditioning was discontinued (leaving all models with the manual air conditioning), and the manual transmission was dropped, leaving all models with a four-speed automatic. The "L200" and "LW200" names were discontinued. Both L-Series sedan and wagon models were officially renamed "L300," adopting a trim level structure like that of Saturn's Ion compact. The previous L200/LW200 were now the L300.1, powered by the 2.2L Ecotec and having no available options. The L300.2 was powered by the 3.0L V6 and had the same range of options as before. The L300.3 had the chrome alloy wheels and a standard power driver's seat, and was unique in offering the "Premium Choice Package." This offered the choice between OnStar, rear DVD entertainment, or (on sedans) a power sunroof at no extra charge."

Frankly, since the L Series already had a model name history I don't understand why the just didn't leave it alone......oh well.

(It's interesting to note that the quote states Saturn discontinued the automatic air conditioning "[leaving all models with the manual air conditioning]." It was either a simple cost consideration for production or perhaps Saturn discovered too many irregularities and complaints about the about the auto a/c. )

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Old 03-06-2013, 05:11 PM   #8
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Default Re: 2004 l300 - p0421

"its a 6 cyl...and it threw the code again last night...the new O2 sensor will go in this weekend"
But your stats say 2.2L which is a 4 cyl. I'm confused.

Mike

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Old 03-07-2013, 12:34 AM   #9
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Default Re: 2004 l300 - p0421

Whether this is a second car not listed or incorrect car stat may have to wait until the OP fixes the problem. Perhaps he'll see and clear this up for everyone...............but this thread is about a V6 L300 as he pointed out in post#6.

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Old 03-07-2013, 12:35 AM   #10
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Default Re: 2004 l300 - p0421

Whether this is a second car not listed or incorrect car stat may have to wait until the OP fixes the problem. Perhaps he'll see and clear this up for everyone...............but this thread is about a V6 L300.

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Old 03-07-2013, 10:27 AM   #11
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Default Re: 2004 l300 - p0421

Quote:
Originally Posted by south42 View Post
My understanding is that the bank 1 (firewall side) pre-cat converter is bad, or the O2 sensor downstream of the bank 1 pre-cat is going bad.
You're right, FDryer, it must be a V6. The statement above won't apply to a 4 cylinder engine. An error must've been made when entering the vehicle information on south42's account.

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Old 03-08-2013, 03:17 PM   #12
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Default Re: 2004 l300 - p0421

Sorry for the confusion...got a little click happy when setting up account...

New O2 sensor went in last night, so far so good...just for good measure, I soaked all the bolts to remove the cat convert pipe assy just in case.

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Old 03-08-2013, 03:55 PM   #13
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Default Re: 2004 l300 - p0421

Thanks for 'unconfusing' some of us.

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Old 03-11-2013, 08:23 AM   #14
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Default Re: 2004 l300 - p0421

Made it about 300 miles and threw code again...looks like I will be shopping for the cat...

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