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  #1  
Old 01-25-2012, 01:47 PM
rotor57 rotor57 is offline
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Default 2005 Altima 2.5L P0420 Code

A couple of weeks ago I had a P0420 code pop up. I cleared it and it came back today, roughly 400 miles later. The car has 143K miles and I'm guessing its time to replace the O2 sensors but looking through the threads the horror stories of pre-cat failure have me concerned. Since the recall doesn't address the 05 model did Nissan fix the problem prior? Is replacing the O2 sensors the best place to start?
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  #2  
Old 01-25-2012, 06:33 PM
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Quote:
Since the recall doesn't address the 05 model did Nissan fix the problem prior?
No. Unfortunately they didn't.

Quote:
Is replacing the O2 sensors the best place to start?
Usually it doesn't. But you could try reprogramming the ECM first.

There are two bulletin for this code. One suggest reprogramming the ECM (NTB10-083) and the other one are for California cars that suggest replacing the cat (NTB09-046)

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  #3  
Old 01-26-2012, 12:19 PM
DCARLTON DCARLTON is offline
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Start with the simple stuff and work towards the more involved (expensive) stuff.

If you are the original owner of the car, you know if the car has been taken into the dealer and had the re-programming done. This re-programming was part of an earlier recall that was supposed to help the timing of valves opening and closing and allowing heat and controlling the 'suction' of cat material back into the engine. I don't know the specific years of the recall; if yours hasn't/wasn't done, Nissan can do that for you.

If that has been done, they can also determine if the P0420 code is the result of a bad pre-cat. If they determine the pre-cat is not a problem (this will most likely be the result), then you have a a couple of options.

Since the car has over 100,000 miles, I would replace both O2 sensors and see if the problem goes away; this has been known to correct the code even though the code is a pre-cat code, not an O2 sensor code (and you are over due on this anyway). If the sensors detect a difference in the before and after values, the P0420 code will be thrown. However, if a O2 sensor is flaky, the values will be different sometimes (and sometimes the O2 sensor will correct itself and your light will go off, only to come back on later).

Replace the O2 sensors and see what happens. They are fairly inexpensive and easy for the DIY'er. Once the O2 sensors are replaced, drive to your nearest Autozone, Advanced or other parts store that can read the codes and reset them or read through the threads here to find out how to reset the codes.

If you drive it for about 2 tanks of gas and the light hasn't come back on, you will know your issue is corrected. If not, then your pre-cat may need replacing and you can do that too, buying the part from ebay for much less than the dealership.

If your pre-cat is at fault, you may notice a higher consumption of oil than normal. Our 2002 had to have its oil replaced by 3500 miles (200,000 miles) or it would be down a quart. It was consistent and I knew what to expect. You should know what is normal for your car as well.

Don't assume the worse (engine/cat failure). I'm not saying it is or isn't the cat, but it isn't always the worst of our fears.
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  #4  
Old 01-26-2012, 01:23 PM
rotor57 rotor57 is offline
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Thank you both, gentlemen. I'll start with the ECM and work my way up.
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  #5  
Old 01-31-2012, 12:21 PM
bracketchev1221 bracketchev1221 is offline
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I had the same issue. The code would come in, then go away and then come back. I replaced the cat, 2 sensors and the plugs. I bought the NGK sensors off ebay and a Walker direct fit cat. It was an easy swap. Mine had 167,000 on it when I changed it. I think it was a total of $450 in parts.
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  #6  
Old 02-05-2012, 07:41 AM
bsalsber bsalsber is offline
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Default same P0420 Code

I just got the same P0420 code in my 2005 Nissan Altima 2S (101,000 miles).

I took the car into Pepboys and they said I would probably need to replace the catalytic converter and O2 sensors. Quoted me around $1,200.



How much should I expect that to cost? Is this mechanical problem normal for Nissan Altimas?

I bought it certified pre-owned at 93,000 miles.

Should I expect future mechanical problems like this? I've thought about selling it after I fix it. However, if it will last me at least three years I'll keep it.
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  #7  
Old 02-05-2012, 07:09 PM
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Check this out:

OBDII Code P0420 - Catalyst System Efficiency Below Threshold Bank 1 | Engine-Codes.com
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  #8  
Old 02-06-2012, 06:33 AM
DCARLTON DCARLTON is offline
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bsalsber - read the above posts before committing to spend 1200.

The O2 sensors should be replaced, you're at 100k; any mileage you get on a O2 sensor over 100k is a bonus. Replace both at the same time with the same brand (NGK preferred, Bosch will work). If your 420 code goes away, then you're done. Once they are replaced, make sure your codes are reset, Pepboys should be able to do this for you, Autozone definitely can. The O2 sensors should set you back $120 or less depending on how much you shop around. The best prices appear to be either Amazon or your local Advanced Auto Parts.

Replacement is simple and they were color coded on the 2002, probably the same on the 2005. Unplug, unscrew the old, screw in the new and re-plug. Get the ones for the car, do not get the Universal fit ones where you have to change the wiring.

If this doesn't fix the issue, then your pre-cat would be the next likely suspect. This is not a hard job if you are mechanically inclined, dedicate 2-4 hours to the job and you can get it done yourself with a minimal amount of tools.

I'm betting on the O2 Sensor replacement fixing your problem.

Edit:
The link above assumes 100 percent working O2 sensors. In a perfect world with new sensors, the assumption is true, however, the first paragraph of the link Benny posted gives you an idea as to how the P0420 is diagnosed.....it uses readings from THE O2 SENSORS. If one is bad, going bad, flaky or slightly out of spec (but still responsive enough for the ECM to see it), it will still function in its handicapped way and not throw a code for a bad O2 sensor, but will effect the readings before and after the pre-cat. Don't immediately suspect the pre-cat as the problem unless you know the other less expensive parts are working 100 percent as expected.

Last edited by DCARLTON; 02-06-2012 at 06:37 AM.
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  #9  
Old 02-06-2012, 09:30 AM
bsalsber bsalsber is offline
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Thanks for the help. I think I'll have the ECM checked out first then take a look and see where I need to go from there.

Just want to get as much mileage out of my investment as I can before I upgrade in car.

I would do it myself but I'm mechanically inclined although I love learning about how engines & cars work.

I'll report back soon the details.
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  #10  
Old 02-21-2012, 09:13 AM
bsalsber bsalsber is offline
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Well I took the car into the dealership yesterday and was told the diagnosis is an engine intake valve leaking.

How can this relate to a P0420 code?

They gave me an estimate to fix it for $2,000. I declined and am tentatively selling it this weekend to a buyer.
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  #11  
Old 02-22-2012, 08:25 AM
DCARLTON DCARLTON is offline
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That's the funny thing about the 420 code, it gets triggered for something that may have nothing to do with the pre-cat.

I'm not sure I'm buying the leaky valve, but I'm sure an expert will chime in.
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  #12  
Old 02-22-2012, 09:43 AM
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You can minimize the cost if you do this:
1. Do a compression test. The cylinder that is really out of specs is the source of the problem.
2. If you tackle the head removal and confidence to put it back then take it to the machine shop for the valve job.
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  #13  
Old 05-27-2012, 08:08 AM
tr1989 tr1989 is offline
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Default not O2 sensor, its crankshaft!!

P0420
Injector cleaner was a temp fix on my 2005 Altima S at 130k. We baby this car and well maintained. it seems the Nissan P0420 code overrides other codes. This maybe why no crankshaft code, but the fix so far is the crankshaft sensor!
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  #14  
Old 10-22-2019, 11:50 PM
[email protected] kleavitt1967@gmail.c is offline
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Took my 2005 Altima to United Nissan to have the P0420 fixed which I read was because of the faulty ecm module and they said they'd reprogram it. But after arriving they quoted me almost $3000 to repair everything else. When I declined they refused to reprogram the ecm because the check engine light was on and didn't do a damn thing to the car.
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  #15  
Old 10-23-2019, 11:33 AM
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If your car has over 100k miles and oxygen sensor hasn't been replaced and I don''t know the maintenance history. You might want to replace the Upstream Oxygen Sensor first. I know the sensor has its own trouble code and you say why would I do that when there's no error code. But the oxygen sensors live inside the CAT. It is very easy to replace specially if you have the QR25 engine.
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