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  #1  
Old 01-23-2013, 05:28 PM
altimaengr altimaengr is offline
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Default 03 altima p420 code

Hi,
I am new to this forum. My 03 altima has been on a roll for about the last year after nearly 100,000 miles with no problems (bought it used)
Fought a stumbling condition that would last just 2-3 minutes then sometimes would be fine for over a month-when I was driving 500 miles a week then. Dealer had it for 3 days and could not figure it out-would not act up long enough. i changed one ignition pack and it seemed to be ok for over 6 months@500 miles a week. It started acting up again and light would not reset it self. I am getting a persistant P420 code. (Engine miss was a different code)Engine has all sorts of power (despite the piston slap-another story) so I am thinking cat is not plugged.
Question; does this code mean I should be changing the upstream O2 sensor or both sensors to get the light to go out?
Bought this car used with about 30k miles and drove it 100k miles with no probs except for the piston slap (which I nursed along with careful driving when cold)
Help and thanks
altimaengr
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  #2  
Old 01-23-2013, 06:10 PM
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Quote:
Question; does this code mean I should be changing the upstream O2 sensor or both sensors to get the light to go out?
It's possible but very unlikely. Usually when you get the P0420 code it ends up to be the catalytic converter. You could try using high octane gas and fuel additives, sometimes just using high octane gas will fix the problem.
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  #3  
Old 01-24-2013, 02:54 AM
altimaengr altimaengr is offline
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Default thanks for the reply

I ran 2 cans of "Cataclean" through it with no improvement
Thought I read somewhere that the 420 code meant I should be looking at only one of the 2 O2 sensors
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  #4  
Old 01-24-2013, 05:38 AM
DCARLTON DCARLTON is offline
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Before assuming the problem is the pre-cat, when is the last both O2 Sensors were replaced? If you don't know or it's been over 100,000 miles ago or never, buy 2 O2 Sensors, same brand, replace them, clear code and see what happens.

O2 Sensors help determine pre-cat efficiency by the ECM comparing values from one to the other. An O2 sensor may be going bad but may not be bad enough to trigger the O2 sensor code but be flaky enough to produce results different enough to trigger the P0420 code (thinking the pre-cat is not efficient).

If you replace both sensors and clear the code and the code returns, then your next step would be to replace the pre-cat. In attempting to fix a problem, start small/cheap and work up.

You can get a scan tool that will read the O2 sensor stream and see what the results are but as I said, if over 100k miles, they need to be replaced anyway before you do anything else. 2 O2 sensors will cost you 1/2 of what a new pre-cat would set you back.

Good luck!
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  #5  
Old 01-24-2013, 07:55 AM
altimaengr altimaengr is offline
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Default p420 code response

Thank you
Never replaced the sensors so I will order from Rockauto today ("Denso" brand is showing as OE)
Just bought a scan tool but It does not do "live" readings as far as I know
Like I said car still has all sorts of power
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  #6  
Old 01-24-2013, 09:16 AM
altimaengr altimaengr is offline
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Default thanks again

Do I need to use antiseize when installing the new O2 sensors? Is there a rule about that?always?never?
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  #7  
Old 01-24-2013, 10:41 AM
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Originally Posted by altimaengr View Post
Do I need to use antiseize when installing the new O2 sensors? Is there a rule about that?always?never?
If available use anti seize on the sensor. Usually all new sensors come with a small pack of anti seize.
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  #8  
Old 01-24-2013, 11:45 AM
DCARLTON DCARLTON is offline
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Most of the sensors I have bought have a cap on the end of them to protect the threads which already have the anti-seize on them.
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  #9  
Old 01-24-2013, 11:57 AM
NissanAltima01 NissanAltima01 is offline
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Don't forget to purchase an oxygen sensor socket and some PB Blaster. All oxygen sensor sockets are the same size and the PB Blaster will help loosen the oxygen sensors.
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  #10  
Old 01-24-2013, 12:33 PM
altimaengr altimaengr is offline
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Default O2 sensors

Thank you all for the information
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  #11  
Old 01-24-2013, 12:45 PM
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I agree. At 100k miles the O2 sensors have reached its upper limit. It may still be working but slow in its response due to soot covering the sensor. Replace both upstream and downstream. Use NGK/NTK, it comes with anti seize. Also replace your spark plugs (NGK) also in its upper limit. Erase the code. If the code returns take note how much time it took to come back. If Chevron gas is available in your area I suggest you use it whenever you can. All Chevron gas grades has Techron that keeps your injectors clean without the need for additives.
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  #12  
Old 02-02-2013, 03:26 PM
altimaengr altimaengr is offline
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Default Code came back

Well the oxygen senosrs came out with needing the special socket or PB blaster, I was surprised how the fasteners held up
Unfortunately the code came right back...16 miles and the 2nd time it was warmed up (I have about 8 miles to work)
I cleared the computer and the light came back on the same way again
I am getting the P420 code so I am resigned to changing the converters
I am looking at the Walker brand on the Rockauto website

Does anyone have any insights?

thanks
P.S. Also does this site (or somewhere else) give a good sequence of operations and bolt torques

Last edited by altimaengr; 02-02-2013 at 03:34 PM.
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  #13  
Old 02-02-2013, 07:19 PM
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check with amazon also you might save $$$ in shipping. you also need a new EM gasket, and new flange gasket used at the bottom of CAT assy. removal, assembly, and torque specs are found in Engine Mechanical manual in Knowledgebase section. you don't need to remove the engine under cover as manual says.
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  #14  
Old 02-03-2013, 11:07 AM
altimaengr altimaengr is offline
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Default thanks

thanks, I would not think of Amazon for car parts
Do you think I should change both cats at the same time?
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  #15  
Old 02-03-2013, 01:28 PM
NissanAltima01 NissanAltima01 is offline
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These catalytic converters are expensive. The one at the front of your engine is going to cost you at least $500+. So if you are thinking of changing the one underneath the car you might want to test it first and i'm sure the one in the front are the only ones going bad in these cars.
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