I have a FED spec, 2000 Maxima SE. Recently had the Warpspeed Y-pipe, 2.25" Test Pipe, and 2.5" SRS catback installed. After 500 miles, the CEL came on for these following codes.

1. P0325 (Knock Sensor/Circuit Bank 1)
2. P0138 (Rear O2 Sensor Bank 1)
3. P0139 (Rear O2 Sensor Bank 1)

During the Y-pipe install: The mechanic cutted the Rear 02 Sensor wire, soldered it back, then added some kind of anti-seize on the Rear 02 Sensor and reinstalled it on the new Warpspeed Y-pipe. The 3rd sensor after the catalytic converter is not plugged in because there was no O2 bung on the test pipe or catback.

Here are my questions:

1. Will cutting or adding anti-seize on the O2 sensor cause the CEL for P0138/P0139?
2. Will the code P0138/P0139 cause code P0325?
3. Does the 2000/2001 Maxima require the 3rd sensor after the catalytic converter to be plugged in?
4. What's the best fix to all of these problem? Replace sensors or an O2 simulator?

 

I have heard cutting sensors causing faulty signals, but unless you installed antifoulers (has worked well for others), the code seems legit even if it is working properly. Install anti-foulers on the secondaries. Anti-sieze should be applied to bolts/sensors that may be prone to rust and will be removed at a later interval. This allows removal without damaging things and creating more work unnecessarily.

 

Edited: Sorry, two threads with code questions. Got the two blended.

 

I'll look into installing the antifouler on the rear o2 sensor. Do you know if the 3rd sensor after the catalytic converter need one as well or be plugged in?

 

I'm not as familiar with the 5th gens. Check out the header threads for the 3.0 on remedies. But the only two ways to illuminate a code is either sim or antifoulers on secondaries.

 

So here is the O2 Sensor Diagram for the FED spec 5th gen maxima.

http://nissanhelp.com/diy/maxima/pro...2_sesnor_1.gif

Since I have a test pipe on, would it still throw a code if I welded an O2 bung to attach the rear O2 sensor that's after the main catalytic converter (Reference to O2S2-B1 on the diagram)?

If I do decide to weld an O2 bung on, is the correct size a 14mm? I remember reading somewhere that the rear O2 sensor is smaller than the two front O2 sensors which are 18mm.

I also read somewhere that an O2 simulator/anti-fouler is pointless if the O2 sensor is not in the exhaust pipe? Can someone confirm this?

I remember also reading something about a resistor trick with 2x25ohms 25 watts resistor in series to the O2 sensor that will get rid of the CEL...

 

Today I decided to get the Rear O2 bung welded on. Cost me $28.10 to get it done ($4.10 for the O2 bung, $24 for labor). Good deal! Hopefully the code does not pop up again. For future reference to anyone who is wondering about the size of the O2 bung, it is 18mmx1.5 thread pitch. Case closed

 

Yes, must hook up the sensor or sim it. You might end up needing an antifouler. You will need to clear your codes and see if the light comes back on. You need to wait for at least 100-150 miles before rechecking. In my experience it takes that long for an O2 code to be thrown.