So i've been having this o2 sensor problem for close to a year now and just dealing with it. When the light first came on I took it to Auto Zone to read the code and they said one of the sensors was throwing the code which was P2A03. I never got around to replacing it and so a few months later I started to notice a dramastic drop in my gas mileage from 19 city down to 13. I took it back to have the code read again and it had an extra code saying the other o2 sensor was out as well. (for those that don't know, I'm reffering to the sensors on the exhaust manifolds).

So yesterday I decided to fix the problem. My car is an 06 5AT. I have another 06 6MT that runs just fine. I decided to take the o2 sensors out of the 6MT and put them in my 5AT because these sensors new are over 200 a piece from the dealer and didn't want to buy a nonreturnable item which I wasn't 100% sure was the problem. I was told by the parts guy at Infiniti that they were the same. So after doing that I resetted the computer and started driving it around. The damn light came back on again. This time I decided to take it to a shop to have it properly diagnosed.

So the mechanic puts the scan tool on it and I'm there watching and talking with him. He then tells me bank 2 o2 sensor is bad and then scrolls down to show the numbers that the sensors are reading. Bank 1 sensor was pretty much staying in the low 1.30's but bank 2 was a little more erratic. It would go from 1.30 then drop down to the teens then would go up to the 1.70's. This erratic reading is what throws the SES light.

I don't understand this. I took a sensor out of a perfectly working car and my car is still throwing a code. I'm thinking this is something other than an o2 sensor problem. Are there other things that could make an o2 sensor read erraticly like that? Maybe a clogged injector or something? Any help is appreciated. I'll probably post this on some other forums just to get all the help I can.

 

Is the 06 an HR or revup motor, because i think the HR runs wideband sensors as std, not sure about the revup though.

 

The sensors are the same on both. I did come across this though while I was searching around. I'm thinking this is the problem as I did reuse the old gaskets from my oem cats when I installed the HFC's. Lately, I have been able to smell gas in the cabin but I attributed it to the fact the ecu was running a much more rich mixture to make sure the engine doesn't run lean since it didn't have the sensors working to go by. I was just thinking the smell was coming out of the rear of the exhaust. I never thought an exhaust leak downstream of the sensor would make it act up like that though.

http://my350z.com/forum/maintenance-...-ses-code.html

 

The main sensor is quite close to the first cat pipe join, so i guess a leak could cause air to be drawn in due the exhaust pulse, and so causing bad reading, IE a false lean, so the ecu responds by making the mixture rich, hence the bad fuel consumption.

 

yeah, I'll find out when I change the gaskets.

 

did you get to solve this issue?

 

It was from an exhaust leak b/w cat and Ypipe.

 

Man i know this is llike 10 years old but ive been having the same exact problem for like a year now. I really hope its just an exhaust leak because ive spent like $600 0n o2 sensors in the last year lmao.

 

if your exhaust is all OEM then you may have an exhaust leak. If you have test pipes like I had then you'll need to google "megan racing o2 extensions". That's what cured my problem.

 

I have the stock cats with a cat back right now. I did have test pipes with the extension but still had the codes. It still backfires and looses power so its probably my sparks or injectors.

 

So what would end up happening if I just left the o2 sensors out? I've been working to put them back in, but I was wondering if I would lose an extreme amount of power. To be completely honest my 0 to 60 currently is in 17 seconds, would the o2 sensors be to blame??

 

The downstream O2 sensors? U can leave those out. They wont affect engine performance at all. Obviously with the hole plugged.

The upstream sensors, they will make ur engine run like crap.

 

Could a leak around the cats put an engine into limp mode?

 

doubt it cause people run test pipes all the time with no limp mode

 

Welll...I'm not sure the above it quite true. A lot of things can put a car into limp mode. Dead O2, bad cam or crank sensor are examples. Unplugging or a dead intake air sensor or a bad MAF are also possible items.

I don't know that a leak around the cat would cause it, it would more likely flash that it wasn't reading right and you would get an error.

First question is, what other errors are you getting?