PO430 to remove the catalytic converter or not

[cptkirkh]

I have 2005 pathfinder with 144,000 miles. Ok so i got the service engine soon light. I checked the code and it was a PO430. Everything works great on the the vehicle. After the light went on i went on a 500 mile trip and the light went out. Then after a month of being home it came back on. I bought a odb ii adapter to check the voltages on the O2 sensors and here is what it shows.

bank 1 senors 1 shows .4
bank 1 senors 2 shows .4
bank 2 sensor 1 shows .6
bank 2 sensor 2 shows .4

from what i read those are normal and it really must be the cat that is the issues. is that what everyone elses thinks also? if so has anyone tried a replacement cat you can buy for 250 online? Thanks

[smj999smj]

Oxygen sensors have a constantly varying voltage, ranging from 0 volts up to approximately 1.1 volts, cycling up and down as the mixture goes from rich to lean. P0420/430 codes are for catalyst efficiency and in order to test a converter for efficiency, one must be able to graph the oxygen sensor signals on one particular bank and compare the frequency of rich-lean cycling of the pre-cat sensor to that of the post-cat sensor. These has to be tested under a certain condition, usually engine fully warmed up and vehicle driving and engine at a specific RPM range. Conditions for testing will be listed in the factory service manual, along with other diagnostic tests to determine the cause of said trouble codes. As a general rule, the post-cat sensor will cycle approximately half the frequency of the pre-cat sensor if the catalytic converter is operating efficiently. A ratio close of 1:1 would indicate an inefficient catalytic converter, meaning that it is not breaking down the exhaust emissions properly. For those vehicles that use air/fuel ratio sensors instead of front oxygen sensors, which look very similar, the air/fuel ratio sensors operate at a much tighter range, usually 400-600 millivolts and even with a scantool can be difficult to test for catalytic efficiency. Bottom line, upstream catalytic converters failing on R51's are not an uncommon problem. If there are no other codes, the engine is running well and there are no exhaust leaks, chances are pretty good that the cause of a P0420/430 code is a bad upstream catalytic converter. As far as aftermarket converters, it's best to stick with a well known brand, like Bosal or Walker. There have been some issues with lesser quality catalytic converters not fixing the problem or not lasting very long.

[cptkirkh]

i ran the engine like it said in the service manual and then reved it to 3500 RPMs and here is the graphed output from torque pro



"https://drive.google.com/file/d/0B6O2a1 ... sp=sharing"

[smj999smj]

All those graphs show only one cycle of each sensor. You're going to need to graph over a longer length of time and count each of those cycles for the front and rear sensors and compare. Also, P0430 is specific to Bank #2, which, on your vehicle, is the left, or "driver's side," bank, so you only have to graph the Bank 2 sensors. Personally, if you don't have any exhaust leaks and the engine is running well without any additional codes, I would resign myself to the fact that I'm going to need a upstream, driver's side, catalytic converter. I had mine replaced at around 85000 miles on my '06. If you don't want to spend the money, you can sometimes "trick" the ECM by installing an O2 sensor spacer on the rear, Bank 2 oxygen sensor. Be advised this will not pass an emissions inspection if seen in some states.

[cptkirkh]

Thanks for the advice and you are right i guess i just need to bite the bullet and pay for it. When you replaced yours did you go with Nissan or aftermarket? Thanks.

[smj999smj]

Mine was actually replaced right before I bought it under Nissan extended warranty, so it was a Nissan part.