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My wife has an 05 Nissan Altima 2.5 S. For the last 2 years it has had a P0420 code that I have used a scan tool to erase a half dozen times in those 2 years. I recently started researching the problem on the internet, and I have found some pretty scary stuff out there. Some say that if the cat is bad it can start to disinegrate and the particles get sucked back into the cylinders causing wear and oil loss. It seems to me that if the cat is a little plugged up it could cause more back pressure on the engine, but the only way particles could be sucked back into the engine is if the exhaust valves are bad. I plan on doing the infrared thermomoter check to see if there is the 100 degree difference, but I will have to upgrade my scan tool to be able to see if the post O2 sensor is reading as it should(my current tool only reads codes). What are your thoughts on this? I did notice in the last oil change it was a quart low, so I am worried that I have some engine damage.
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Unfortunately this is an all too common issues with the 2.5 and some of the 3.5 engines. The only true way of diagnosing the symptom is to drop the cat for inspection. Good luck!.
p0420 three way catalyst function.have you checked
the exhaust before the o2 sensor for leaks? pull your
plugs to see if fouled. either the catalyst efficiency
is gone in the cat or the engine is having a problem and
killed the cat. have you tried a compression check? also try doing
a power balance test.what have you tried so far?Here is some stuff to check for this problem. Please note that the cat is bad at the end, after all others check ok.
Sensor heating or heater solenoid faulty
Connector terminal contact is damaged or corroded
Wire harness – Check harness for correct voltage, open, short to ground or short to voltage
Update control unit software – Check for the latest control unit update
Powertrain or Engine Control Module faulty, needs to be ruled out
HO2S sensor contamination/damaged
Exhaust leaks or restrictions
Catalytic converter improper operation or physically damaged
Please move with care as it can get well expensive to fix it, make sure you check the sensors, it is cheaper than the cats.How many miles are on the car? I have a 2001 Nissan Maxima and I had the same exact code but I never heard of particles being sent back into the engine. My cat has been bad for over a year and nothing that I know of affected the engine so really you shouldn’t worry. Especially if its been like that for over two years. The code could also be a bad sensor reading so check your o2 sensors going into the cat which in my car was the bank 1 sensor 2 o2 sensor I don’t know about your car though. If your cat is bad then you should replace it. I got mines replaced about a week ago and the code hasn’t popped up since. Good luck.
The 2.5 QR25DE engine from Nissan is plagued with issues. Nissan actually recalled allot of the 03 to 06 Sentra’s and Altima’s due to engine issues, mainly excessive oil consumption. This stemmed from a incorrect break in period at the factory.
They are also known for the butterfly screws on the throttle body plate to be sucked in to the engine as well as pre-cat failure also.
There is also recalls to reprogram the PCM to help reduce the chance of Cat. damage by adjusting the fuel ratio’s.
This engine was discussed a few times on the old forum site so i would recommend doing a search.
If you start noticing excessive oil consumption, the only true fix is to rebuild the motor. It would be pointless using a junk yard unit as it may contain the same problem.
Good luck and keep us posted.
[quote=”dreamer2355″ post=31303]The 2.5 QR25DE engine from Nissan is plagued with issues. Nissan actually recalled allot of the 03 to 06 Sentra’s and Altima’s due to engine issues, mainly excessive oil consumption. This stemmed from a incorrect break in period at the factory.
They are also known for the butterfly screws on the throttle body plate to be sucked in to the engine as well as pre-cat failure also.
There is also recalls to reprogram the PCM to help reduce the chance of Cat. damage by adjusting the fuel ratio’s.
This engine was discussed a few times on the old forum site so i would recommend doing a search.
If you start noticing excessive oil consumption, the only true fix is to rebuild the motor. It would be pointless using a junk yard unit as it may contain the same problem.
Good luck and keep us posted.[/quote]
+1
I took the car to autzone a few years ago to get the code read before i bought my own code reader(before all the P0420 codes) and they told me it was an O2 sensor. Is there a code that will set that tells you the O2 sensor itself is bad? Didnt think of it much till now, I will have to test the post cat O2 sensor.I also wanted to mention I took the car in for a bad crank sensor a couple of years ago(after the MIL had already been lit) and the dealer said that they cleared the codes and re flashed the ECM and replaced the crank sensor. They mentioned the P0420 code but said “it could have been a piece of trash that got caught in the cat as a random thing and if it happens again we will go ahead and replace the cat”. Now I am hoping that mabe the extended warranty I paid for is still in effect and will cover this otherwise its all in my hands.
A P0420 does not mean the O2 sensor is bad, it’s more likely to be a bad catalytic converter. You can verify this by looking at the live data on a scan tool. You’ll need to have one that can do this. Pull up the readings for both the front and rear O2 sensors. The front sensor should switch back and forth over .5v fairly rapidly whereas the rear O2 should stay pretty steady near .5v. If the rear sensor switches at a similar rate to the front sensor then the catalytic converter is not working and that is the reason for the code. if the sensor stays steady around .5v (I don’t think this is likely with that code) then perhaps there’s a wiring issue or an issue with one of the sensors themselves.
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