Error Code P1148 on 2002 Nissan Xterra

Hi all,

I have a question about the severity of a check engine cody that has been coming up on my 2002 Nissan Xterra. It is currently giving an error code that states P1148. When I googled it, it stated the following:

“The Diagnostic Trouble Code (DTC) will set when the closed-loop control function for bank 1 does not operate even when the vehicle is driving in the specified condition, the closed-loop control function for bank 2 does not operate even when the vehicle is driving in the specified condition.”

A little background info. My catalytic converter has been bad for several years but in the state I live in I am not required to fix it nor do I have the money to do so just yet. I am not sure if this had anything to do with this code.

What I’m curious if any of you could tell me is if this is something that is detrimental to the performance of the vehicle if I do not get this looked into immediately? I have not noticed any substatial performance degradation in my vehicle in the recent few days since the light has come on except for every once and a while a bit of a strong fuel smell when I start it. I have noticed an error code P1143 code which will come on as well and has to do with air fuel ratio. However, everything I have found online seems to mention it is not majorly detrimental to the functioning of the vehicle except for fuel economy. And I have not noticed a major decrease. I noticed when I was looking into error code P1148 that other error codes would come up as well that were of similar nature. Any insight provided is much appreciated and thank you all very much.


You try to fix 1 thing then another issue pops up.

The code indicates the heated O2 sensor is not function. Causing the computer to remain in the open loop mode.

So the computer is going to operate the engine as if it never reached operating temperature.

The most likely cause for this code is a failed heated O2 sensor for bank 1.


I think that is the story of my life with cars. It seems like it’s only a matter of time before your next car bill.

Thanks Tester. Do you know if you can drive for a few months without it causing further damage? A lot of what I’ve read just states you lose fuel economy. Also, do you know if an oxygen sensor is very difficult to fix on my own?

If you own a floor jack, a set of decent jack stands (or some extra wheels to place under the front wheels), and the necessary tools (wrenches, breaker bar) it’s not difficult at all. If doing it yourself, the parts are not expensive either, when purchased online from RockAuto.

Also, even if you are not required to pass an emissions test, I would still replace the oxygen sensors, in order to maintain efficient operation. I would not spend the money on catalytic converter(s), nor would I spend money trying to repair evaporative emissions leaks unless required to pass an emissions test. Even then, there are techniques which will allow one to get a car through emissions without paying to fix a problem if it’s a “monitor” which is not continuous.

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Here’s where the O2 sensor is located.

and here’s the tool required to replace it.



Thanks bcohen2010 for this insight. Super helpful and I very much appreciate it.

Thank you so much Tester. You really helped me out a lot!!!

So I looked into the 02 sensor part on and I found options from $20-$47 per unit. I don’t really know if theres much difference in the quality of these units. I also saw that in the specifications of some of these models it said something like “upstream left or downstream right” could you explain what this means? Is this particular unit listed below one that would fix the issue? Also, do I need to replace more than one sensor or is it just one? Thanks so much!

The code indicated that O2 sensor is sensor 1/bank 1.

Bank 1 is the exhaust manifold on the same side as cylinder 1.


So that means bank 1 is the passenger side of the engine, and sensor 1 is on that manifold.


The upstream O2 sensor is located in the exhaust pipe ahead of the CAT. The downstream sensor is in the exhaust after the CAT.

So would I need to purchase Upstream left Oxygen Sensor? Thank you.