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I'm getting codes p0031 and p1148 on my 2007 Altima 3.5 SE.

From what I've read, p1148 is caused by p0031. P0031 relates to the voltage on the heater circuit of the 02 sensor on Bank 1, Sensor 1.

I know that most likely I just need to replace the O2 sensor, but I'm unsure (after researching for hours) which one I should be replacing.

Does anyone know if this would be the Front or Rear? And if it is downstream or upstream?

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Bank 1 is the same side as the number one spark plug

Bank 2 is the opposite side as the number one spark plug

Sensor 1 is before the catalytic converter

Sensor 2 is after the catalytic converter

Bank 1 Sensor 1, would be the same side as the number one spark plug before the catalytic converter.

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Looking at auto parts sites, they all notate the plugs by front/rear and upstream/downstream. Do you know which one I should be getting? (Also, thanks for the concise info!) – clifgriffin Jul 7 '11 at 14:19
@clifgriffin - I'd consult a Haynes/Chiltons manual to find out where Cylinder 1 is, and that'll give you front/back since your engine is transverse-mounted. Since Sensor 1 is before the catalytic converter, that would be considered "upstream". – Iszi Jul 14 '11 at 20:00

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