A few days ago my 2002 Max's SES came on. I checked the codes and found them to be P0139 and P1147. Acompaning the two codes is a sharp decrease in milage to the tune of about 6 miles to the gallon. The exact number was derived directly from the trip computers calculation. Now, I'm aware of the fact that the trip computer isn't all that accurate, but the decrease in milage is backed up by ancedotal observations taken from my trips to and from home and school. Otherwise, the car runs fine.

I looked up each code:
0139 appearently corresponds to a bad post cat(is that correct?) O2 sensor and
1147 appearently could very well mean my MAF is bad. I'm even more suspicious of the MAF because I have had the "won't rev past 2.5K RPMS" before and because of the 3 some odd O2 and MAF related threads on the front page.
Now, I'm not familiar with my cars intake and exhaust systems so please correct me if I'm incorrect.

I have a new MAF, but its part number 22680-2Y001; the MAF sensor for the 99-01 Maximas. Is there anyway I can forgo spending 500 dollars on the A33B model and use this spare MAF? And I will probably need an ECM reflash as well.

I've searched the forum with no luck as all relivent links point to deleted or incorrect threads.

Thank you.

 

Is your 2nd code P1148 or P1147? You refer to both.

I have had the exact same P0139 and P1147 codes and they are both for the white O2 sensor. I replaced the sensor and all has been well since. If you've never had your ECM updated, it might be a good idea to get this done at the dealership too (should be about an hour or less of labour).

As for the MAF, you can use the 22680-2Y001 MAF and just transfer the thermistor from your existing MAF to this one. This has been done successfully by many people on the ORG.

There are a LOT of links to this stuff on the site, but they are tough to find. If you get to a link that appears irrelevant, change the "showthread" in the link text to "oldthread" and see if that works for you. This is supposed to work but I have found instances where it doesn't, plus if the link is to a specific post instead of an entire thread I don't think it works.

 

P0139 is a downstream of one of the precats, which won't/shouldn't affect fuel maps at all, just light the MIL to say your precat isn't functioning up to par (other meanings too, but mainly dead/failing sensor or bad precat).

P1148, according to the FSM, only refers to O2 sensors:



But not entirely familiar with A33B EC, so my best guess is by the FSM. I'd say replace the O2 sensor, and see what happens.

When my rear O2 (upstream) sensor went out, along with my usual driving, I was getting a worst of 12.x MPG.

 

Its 1147, excuse my mistake. Are there one or two downstream white o2 sensors? I will replace mine and see what happens.

I did not know about the "showthread" to "oldthread" change, but thanks for informing me. I will use that from now on.

 

P0139 & P1147 both refer to the white O2 sensor. Replace that one and you should be good to go. There is only one white sensor. It is a relatively easy job - the clips are a PITA but if you buy a OEM replacement, it comes with new clips so you can just break the old ones to get them off.

 

P0139 corresponds to an 02 sensor with white cable. It should be the second closest one to the front on the y-pipe (atleast thats how it is on 01 FED SPEC)

 

Thank you guys, I will change it when this run of prelims is through.

 

Finally have time to change the sensor and I'm confused as to which sensor to purchase and change.
Finding simple information telling me exactly where each sensor is, and exactly where the white o2 sensor is has proven impossible. Replacement sensors are classified by either number of wires (1,2,3,4) or location (pre/post cat and reward (1) or forward (2) bank). I don't understand exactly which one the white O2 sensor is. Could someone help me out here?

Thanks.

 

Found a sensor
here
Its the one at the top of the page and is marked as "center, under the engine". This is the correct one, no?