Question: Will a malfunctionin O2 sensor decrease mileage? if so by how much. I had this SES light and had the car scanned. It was recording a high voltage reading on the o2 sensor at the rear bank 1 sensor. I just noticed that the mileage on my 01 SE is terrible. Is this a sign that a tuneup is required? if so what are the best plugs for the Maximas?

Thanks for your help.

 

do you have a aftermarket y-pipe?

you could be due for a ECU update, read this to see if it applies to you:
http://maxima.theowensfamily.com/tsb/NTB02-051a.pdf

the secondary o2 is only used for monitoring purposes, gas mileage shouldn't be affected (well at least mine hasn't changed too much driving with the same code)

 

ngk is what ive found runs best whether copper or platnium is up to you. i go with copper since they are 1.69 a piece, burn hotter than plats and are very easy to change in my 01. plats will last longer though. as far as the code, larrio is steering you in the right direction. i had the same code a while back and nissan replaced both secondary o2 sensors and flashed the ecu. the code you are getting for the o2 sensor will not affect mpg since it only monitors the precats.
do the regular check list for plugs, pcv, air filter, clean throttle body and fuel system. also check tire pressures as they will drop when it gets cold out. i am not sure of your weather patterns or fuel reguations but when its gets cold in certain parts of the US, they add alot more additives to the fuel which add to decreased mpg.

 

Larrio/Sloppy Max:

Thanks for the advise. I'm not sure if the Max I have came with aftermarket Y-pipes. It's the 2oth anniversary ed and I just got last Tuesday. I have not had the chance to inspect the whole set up as temps here in Toronto dropped to freezing.

I will definitely do the tune-up and have the wheels aligned. Other than the fuel economy issue, the engine purrs like a cat considering it has 65 k miles.

Enjoy the weekend.

 

since its stock and a AE, just check the tsb to see which version of the ECU you have.

mine is ver.16, which does not apply for the ECU reflash (i'm AE also). But yours could be an older version, especially if you have never gotten a p0420 code

 

When my SES light came on at 28K miles, I had 2 O2 sensor codes. P0139 and P1147. My gas mileage dropped with a quickness. I ended up having both bad ones replaced and reprogramming of my ECU. My gas mileage slowly returned to normal after that.

 

Larrio/CharlieK

I'm leaing towards changing both rear O2 sensors as suggested in the service bulletin that Larrio sent and have the ecu checked if it needs to be reprogrammed. Other than that, I'm just wondering why it took me this long to get a Max. This thing is a dream to drive.

Thanks.