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Discussion Starter · #1 ·
Need an opinion! I purchased my 2002 Nissan Altima 2.5 in 2011 with 150,000. Right after I purchased it, the head gasket went. I had that fixed and the car has run very well since that time. My car now has 211,000 and is still running great except for I am now getting the dreaded P0420 code. Its using oil like crazy and as I have read it's probably the Pre cat. I just want an opinion on If I should go ahead and replace the cat. It has a lot of miles and I realize this, however It's been such a good car and I would like to get 300,000 miles out of it. I am not sure if the engine has been damaged yet. Like I said before It's running fine, but I do have the code. Yesterday we changed the upstream o2 sensor and it was in rough shape. (picture attached). Just wondering if anyone has replaced the pre-cat with this many miles on it and has it been worth it. Like I said I really believe I can get 300,000 miles from her. Do you think I have a good chance of this happening?

Would appreciate anyone's opinion.
 

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Replacing the precat or going with a free flow header is the one of the first things you do as preventive maintenance on l31 especially 02's. I went the header route as it was cheaper and gave me small performance gains. Installation is straight forward and there is write up on the forum if you search it up!
Goodluck!!
 

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ohh geez the dreaded pre-cat issue, i would say get it replaced as soon as possible before it is completely fubared and goes and destroys your motor also
 

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Discussion Starter · #4 ·
Thanks for the feedback.

I am going to replace the downstream 02 sensor and I have ran 1 container of the cataclean through the fuel tank. I will put another container in it after the other 02 sensor goes in. Even if the code disappears, hopefully it will buy me a little more time to get either another pre cat or just go with the headers. Keeping my fingers crossed as I want her to reach 300,000 miles.
 

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Engine using oil the engine is already shot. The cat material has killed the oil rings.

I've rebuilt three engines that have died this way so I know of what I'm saying............good luck.
 

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Engine using oil the engine is already shot. The cat material has killed the oil rings.

I've rebuilt three engines that have died this way so I know of what I'm saying............good luck.
The reason the precat went is that the camshaft and crankshaft position plastic sensors (which are exactly the same part but just in different places)were garbage and should have been replaced with Nissan's redesigned metal sensor back in 2007 when there was a 800000 car massive recall on them. Nissan refused to replace the sensors except if the customer would pay for it (even though still on warranty!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!) Most customers balked and then dealers were told by Nissan to tell the customer that they would reprogram the ECM for free
to fix the problem. 99.9% of the customers went that route. However there were many VIN numbers left off the list. On the ones that were on the recall list and who agreed to get the ECM reprogrammed the problem did not go away completely for the following reason. Nissan reprogrammed the ECM by telling the ECM to ignore the crankshaft position sensor but left the camshaft position sensor unchanged and still in the car. It turns out that you don't need both sensors just the camshaft position sensor. However because they were both the same part, the camshaft position sensor also eventually went bad but not as bad as the crankshaft one because the crankshaft sensor was in a hotter place being right in the engine block. However over time the camshaft position sensor would cause the engine fuel mix to be too rich and the engine would release unburnt fuel into the exhaust and eventually the cats would deteriorate and partially plug and since the DOHC CAM SETUP allows both the intake air valve and the exhaust valve to be both open at the same time and since the precat is so close to the exhaust manifold (bolted on to it) cat materiel gets sucked back up into the engine eventually destroying it. Don't put any more money into that car. Spending money for 2 new cats, 2 new oxygen sensors and 2 new crankshaft/camshaft position sensors, and a new engine would be ridiculous. Don't walk away from that car. RUN away from that car. I have a 2006 Altima which had the crankshaft position sensor ignored by the reprogramming of the ECM. (it was done by the previous owner of the car) but I changed the camshaft position sensor and the 2 cats along with 2 oxygen sensors soon after I bought the used car. Even now I still only hope I saved my engine. In your case it is too late.
 
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