How many O2 sensors are on a 2001 SE?

 

FED Spec or Cali SPEC? 3 FED 4 Cali ?? I know the FED spec has 3 b/c I had a FED spec car.

 

FED spec.
I guess that would be 1 upstream and 2 downstream?

 

all 2001 maximas are cali spec... which means 4 O2 sensors...

 

I didn't know that, Maaf karna bhai

 

I didn't either! But now things are starting to make sense. So that would mean that there are 2 upstream and 2 downstream O2 sensors?

 

is all gooood

 

yeah... 2 upstream that monitor A/F ratio... 2 downstream that sit behind the precats and monitor them....

 

so for Cali-spec (my 2K has 4 O2 sensors according to OBD-II) they only have O2 sensors monitoring the precats, none monitoring the main cat?

 

yes........

 

Thanks UMD~ for the info! I've tested my O2 sensors and there is only one out of the 4 that cycles from .1 to .9. If there are 2 upstream, then shouldn't both of them cycle?

 

the front two O2 sensors should have a relatively short cycle time... meaning they will pulse between ~0V to ~1V quickly. The downstream sensors will have a much longer cycle time. Make sure the system is in closed loop mode so that the sensors have heated up sufficiently.

 

OK...I guess the upstream sensor on bank 1 is bad hence the PO420, because only the front bank 2 upstream sensor cycles.

Also the rear bank downstream sensor makes no change (slow) when I induce a lean or rich condition.

 

Wait a second, I just replaced two on my car and there is one sticking in the front of the main cat, doesn't that monitor the cat. Or do you need one in front and one in back of the cat to monitor it?

 

The way I understand it is - we have 4 o2 sensors and 3 cats. There are 2 pre-cats and 1 main cat. There is one upstream sensor for each precat and 1 downstream for each precat.

The upstream sensor's output voltage cycles and the downstream sensors output voltages are based on lean/richness. The PCM compares the downstream sensor's output voltage with the upstream's (for it's bank) and makes the appropriate adjustment for fuel mixture - which is done by varying the pulse width for the injectors.

 

on a 3.0 max w/ fed. spec. we have 2 up stream at either side of the exh. manifold and 1 down stream just right before the cat.

 

I always thought the PCM used the upstream sensor's output to determine leanness/richness, and made fuel trim adjustments based on the upstream sensors alone... the downstream sensors are ONLY used to analyze the efficiency of the precat catalyst. I know the downstream sensors don't change NEARLY as often as the upstream ones (if they do, the PCM knows the catalyst has failed and throws a catalyst efficiency code)

 

Yeah, Cali-spec (mine's a 2K originally commissioned in NY state, shows OBD-II Calif on my OBD-II scan tool) has 4, 1 upstream on each bank, 1 downstream on each bank, whereas it sounds like FED-spec just has 1 downstream in the Y-pipe before the cat?

Strange how neither have an O2 sensor behind the main cat, which would be the most complete solution...

 

the downstream sensors are used to regulate A/F ratio only if one of the upstream sensors is bad... otherwise, they do nothing.

 

On my 01 Max GXE 5spd I have 4 O2 sensors, One in the manifold on the front- one in the precat- front one, then one in the cattman Ypipe- the middle precat has been eliminated and I get no check engine lite. And the final upstream O2 is accutally in the part of the Ypipe that attaches to the rear exhaust manifold. The main cat- which I also don't have anymore has no O2 sensors in it like the older Maximas used to have. The post cat O2 sensors monitor efficiency of the cattalyst and if the cat has been damaged or removed it will set a check engine light. I am not sure why my car has not set a check engine lite for cattalitic converter below threshold after I installed the Cali spec Y pipe on my car, but as soon as I get my Cattman headers and remove the front precat I should find out if I will get a check engine light- I'm a Nissan tech btw so even if I get a CEL I can install a signal generator in place of the O2 sensor that is going to trip the code for the Cat that is no longer there

 

hehehe... a simple 555 timer circuit and some caps and resistors should be enough to make a pulse generator that simulates the O2 sensors...

 

Fed Spec owns Cali spec....

 

quiet exploder boy

 

I've actually thought of that as well. The PCM wants .1 to .9 with a 3hz frequency on the upstreams and .4Vdc on the downstreams.

Two double pole double throw switches could be used; one for bank 1 and one for bank 2. The output of each switch goes to the normal PCM IN and the inputs to the switches would be o2 sensor output OR home made circuit output. One pole input would be upstream o2 and the other would be the 555 at .1 to .9 @ 3hz. The other pole would be downstream o2 and the other would be .4vDC. So if you had a problem with bank 1...bam!.....switch the switch ...clear the code....and forget about it.

 

yeah but my whole thing about this is... its only if I get a CEL for removing of the precat with the new Cattman headers. If thats the case- I will need to hook up a few radioshack pieces up and make up my own "cat" in a chipset :P I'm not removing the O2 sensors.

 

So BlackBird...does it sound like I have a bad cat or o2 sensor? Should BOTH my upstreams be cycling?...cause only one is. I've got the PO420.

 

Maybe this is a stupid question, but have you had the ecu reflashed?

 

the UPSTREAM O2s have to cycle on and on from like .9 to .1 v or so inbetween... if they stay on one spot for too long U got a lazy O2 sensor and its causing U to get ****ty gas mileage. But then again U will get a O2 sensor dettoriration code.

 

shut it tan maxima

 

I have had it flashed and the code came back within a week.