P0138 code for an SE-R

[civiceater]

Car: 2003 Sentra SE-R Spec V

Here's a thread when the first time I attempted to get help:http://forums.thevboard.com/vi...=0138

Anyway, finally I got my car into the shop at school for actual diagnostics of the code. I used a Modis to do this. I can understand all of the readings at the freeze frame for the 0138 code, but this: "L fuelT % = 109" or something like that. Is that my long term fuel trim? I was wondering what it actually mean. I know for some cars the fuel trim numbers are either between 0-255 (128 at stoich) or -128 to +128 (0 at stoich). What does the 109 mean? Is it at 109 at the 0-255 scale or the latter? Also same thing for what I'm assuming as my STFT is at 104.

Now I also noticed another thing. I dunno why but for some reason the HO2S2 (rear O2S) is switching rather low and it gave me a pretty square wave. Consistent with no dropouts or spikes unlike the HO2S1 (front) which is switching rather normal (which I'll bring up again because it doesn't have a normal time for switching back and forth). Also the signal never went over 300mV. My instructor said that it could be that the PCM is actually not looking at the signal the O2S is producing but rather the change it will make on the reference voltage that the PCM is sending the O2S. So we went ahead and disconnected the O2S from the harness and started the car to see what kind of signal I would get from the PCM. And it looked like this:

(sorry from the crude pic)

And again it didn't go over 300mV. I thought it was weird since the O2S is not sending any signal to the PCM why would I still get something like that?

Now for the HO2S1 thing mentioned earlier. I was looking at it switch and it was rather odd too. For some reason it would switch from lean (low voltage) to rich (high) for a longer period than the rich to lean switch. I mean if it wasn't consistent I'd consider that normal, but it was consistent. My theory is this. If the 109 I got from the LTFT and the 104 from the STFT (I'm assuming) is letting me know that the computer is correcting to go lean, then I'd see why it takes longer to switch from being lean to rich. Does that sound right?

Did any of that make any sense guys? Hope you guys could shed some lights into what I've been rambling about here lol. Thanks.