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Code P0420 (bank 1)


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Hi everyone, 


I haven't had my Pathfinder very long, so forgive me if I'm not attuned to its anatomy.


I'm getting a P0420 code and will be replacing the O2 sensors first. 


My question is, where is bank 1? And is it the pre-cat or post cat O2? Or should I just replace all 4? I didn't realize that this thing has 4 of them.


Thanks for any input...


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Bank 1 is passenger side. Try replacing the downstream O2 sensor first. It’s the one after the cat. “V” configuration engines have 4 O2 sensors. Inline engines (with only one exhaust manifold) have only 2 sensors.

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Common problem starting after 75K. Ultimately, you’ll probably need to do all 4 but I’d do it piecemeal. The post Cat ones are a cake walk, the pre Cat ones are not fun at all. Usual failure code is “Heated O2 Sensor”


O2 Sensors

Bank 1 = 1 Passenger

Bank 2 = 2 Driver

Sensor 1 = 1 Before Catalytic

Sensor 2 = 2 After Catatlytic


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My B2S2 sensor went out about a month ago and getting out wasn't too hard. The bolts for the heat shield were completely gone and if I removed them then there was no putting them back. So all I did was cut the little heat shield tab that comes off and covers the sensor. The second hard part was removed the seized sensor. With a little heat and some force it came out pretty easy. if you do have to heat up the exhaust to get it out, make sure you're heating the outside threads and not the threads of the sensor itself. Most people say use an Oxy torch, but I was too lazy to drag out my hoses so i just used small propane torch and it worked great. took me about an hour and a bit, but most of the time was waiting for the cat to cool off before I touched it.

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