precat/catalytic converter in 2005 2.5S - Nissan Forums : Nissan Forum
 
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#1 Old 11-08-2010, 08:20 PM
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precat/catalytic converter in 2005 2.5S

I have a 2005 2.5S. Last month my engine light came on and I ended up replacing the catalytic converter. Last night, not 3 weeks later, the light came on again and now its saying I need to replace the precat. I have just under 137000 miles on my car and everyone I have talked to said thats low milage to replace all of this. I've tried to research the problem and I'm getting mixed answers. Some say I just need the computer updated by a dealership and others say I need to replace it asap or my engine will go bad. From what I can see this appears to be a pretty widespread problem. Any suggestions?

I'm sorry if this question has been answered before but I was trying to look through previous posts and do other research and I'm still uncertain about what to do. Also, I'm new to this and want to thank you all because in looking up answers to this problem I have learned some new things about my car and things I should keep an eye out for! Thanks everyone!!
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#2 Old 11-08-2010, 08:23 PM
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How did you know your precat was bad the first time the engine light came on?
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#3 Old 11-08-2010, 08:27 PM
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I didn't know. I just had the catalytic converter replaced and now they are telling me that the precat is bad and that's why the light came on. I'm not real familiar with car parts but my stepdad is a mechanic and I'm trying to get as much info as I can before I call him and tell him whats up.
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#4 Old 11-08-2010, 08:32 PM
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I would then replace the upstream oxygen sensor (near the exhaust manifold). This sensor determines if your precat is bad or not. Since you replaced the precat, the sensor is sending an inaccurate reading which is why your engine light is on. I heard most oxygen sensors last around 100,000 miles or so.

I am not 100% sure if it is your upstream oxygen sensor, but that would be the first thing I would replace. This is all assuming the code is P0420.

Last edited by bob1234; 11-08-2010 at 08:34 PM.
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#5 Old 11-08-2010, 08:32 PM
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If the SES light is saying catalyst below threshold, go back to where you bought the converter and ask them for warranty. Don't be shy, ask for FULL warranty, labor included. We see this happen every so often on aftermarket converters.


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#6 Old 11-08-2010, 08:35 PM
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thanks!!
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#7 Old 11-08-2010, 08:49 PM
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You have 2 catalytic converters on your car. Along with 2 oxygen sensors. One sensor is before the pre catalytic converter so it only reads air/fuel ratios. The second sensor is after the pre catalytic converter and before the main catayltic converter. So there is no sensor that can tell you if the main catalytic converter is bad or not. If you had your main catalytic converter replaced which is under the car I doubt it has already gone bad. The pre catalytic converters on the 2.5 altima is known for failing and coming apart which will ruin your motor. Also 137,000 miles is NOT too low of miles to have catalytic converter problems especially with the pre converter. Your second O2 sensor might be bad and might be receiving and sending false readings. But with how many miles you have it is a high chance that your pre catalytic converter is coming apart or clogged. Does your oil level drop between oil changes? Do you check your oil level? A compression test wouldn't hurt either because if they pre cat has started to come apart your motor might be on its way out.

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#8 Old 11-09-2010, 01:45 AM
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Good luck - I'd look at the oxygen sensors as well. If you do end up needing one or both, buy 'em from Amazon. Search for "bosch oxygen sensor" and click on one that comes up, then put in your car info. It'll probably not be the one for the Altima so they'll show you the ones that fit. They're consistently cheaper than any place I've found.
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#9 Old 11-09-2010, 01:45 AM
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Op, which converter did you replace 3 weeks ago?


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#10 Old 11-09-2010, 03:03 AM
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If you decide to replace an aftermarket header without pre-cat, make sure you can remove the CEL after the installation. I replaced mine couple weeks ago, I cannot remove it even I put 2 o2 spacers on the secondary o2 sensor. I didnt try o2 sim, but heard no use for 05,06 alt. If anyone has idea, please tell me. Thanks
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#11 Old 11-09-2010, 03:07 AM
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^^ No fix for that on the 05+ models yet. You will prob have to live with it. Sorry

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#12 Old 11-09-2010, 05:55 PM
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Just to clarify there is no CEL fix for the 05-06 V6 with headers. I have a 05 2.5 with a header and 2 stacked O2 spacers and haven't had a CEL from it. So all 02-06 2.5 altimas can use O2 spacers to keep the CEL off after you install a header.

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#13 Old 11-09-2010, 06:51 PM
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Quote:
Originally Posted by 3rdgen2.5s View Post
Just to clarify there is no CEL fix for the 05-06 V6 with headers. I have a 05 2.5 with a header and 2 stacked O2 spacers and haven't had a CEL from it. So all 02-06 2.5 altimas can use O2 spacers to keep the CEL off after you install a header.
You mean you put 2 stacked o2 spacers on the secondary o2 sensor? I did that, but the CEL on after running 10+miles. How did you make it? where did you buy the o2 spacer?
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#14 Old 11-09-2010, 08:07 PM
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Quote:
Originally Posted by swat518 View Post
You mean you put 2 stacked o2 spacers on the secondary o2 sensor? I did that, but the CEL on after running 10+miles. How did you make it? where did you buy the o2 spacer?
Do you have a 3.5 or a 2.5? Yes I have 2 stacked spacers on the second O2 sensor. I got them from markspecv here on the forums pre-drilled out and stacked.

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