1991 240sx: O2 sensor unplugged but not getting a code

[vancouverbc]

I'm getting other codes but not the code for O2 sensor. The mode 2 self-diagnostic test indicates the fuel mix is good.

[vancouverbc]

Just remembered that the O2 sensor doesnt do anything below 2000 rpm.Ill have to test above 2000 rpm.

[vancouverbc]

I tried over 2000 rpm, and cant trigger the O2 sensor code.

The voltage reading is a little under 1 volt for the O2 sensor.

[180fan]

consistently? That voltage should bounce back and fourth between 0 and 1 volt.

[vancouverbc]

The O2 sensor voltage starts off at around .2 when engine is cold and gradually rises to around 1 volt. I'll have to try this with the O2 sensor connected to ecu. The 1 volt reading at idle does suggest a rich mixture. Not sure how reliable this is.

[vancouverbc]

An old or dirty o2 sensor will read lean so that is not my problem. I cleaned o2 sensor anyway. Before cleaining, I did test the O2 sensor with it connected to ecu. There was no difference during idle(volts were close to 1, still) but above a 1500 rpm, the reading went crazy alternating from .2 volts .4 to .5 to .8 volts. This makes sense since O2 sensor does not attempt to control anything until 1500-2000 rpm. I wish there was a definitive way to know if you are running rich.

[MTX450]

I don't know if this thread is still active or not, but I just wanted to shed some light on a similar problem I am having. I just noticed that the car today was running like crap (usually is) and so I figured I would pull the o2 to see if there was any difference in performance. I know for a fact that when you pull the o2 sensor, you are suppost to get a CEL. Well, in my case, I get nothing. Current symptoms are hesitation between like 2500-3000k and ****ty idle (Need to clean out AIV). Oh, and I get like 20mpg. My question is, what is causing the car not to throw a CEL? Is it possibly a faulty ECU? I have also rebooted the ECU numerous times (starting and stopping motor)

[vancouverbc]

Mine turned out to be a bad ecu. I did get a rich code and other codes worked. As you say, a disconnected o2 sensor should produce code.My symptoms were subtle and only detected by emissions test.

The best place to get ecu is in the forums when people part out their car.

[MTX450]

Thanks!

I'm gonna go get a new o2 sensor, and put it in and see if it does anything...just for the hell of it

If it doesn't help, I will look into a new ECU