Problem with O2 sensor self-diagnostic test

[Kallikak]

I'm sorry if this has been discussed before and I didn't think of the proper combination of keywords to search, but I tried to do the self-diagnostic test for the 02 sensor today as described in the FAQs.

1 - Turn on ignition switch (do not start engine).2 - Turn diagnostic mode selector on ECU fully clockwise.3 - Wait a few seconds.4 - Turn diagnostic mode selector fully counterclockwise.5 - You are now in MODE-II.6 - Start engine and let fully warm up (temperature up to normal).7 - Run engine at 2000 RPM or higher for about two minutes under no load8 - Check that the inspection lamp (red LED) on the ECU goes on and off more than 5 times during 10 seconds at 2000 RPM.

I didn't get the inspection light to come on at all. Not once. The CEL would come on for a few seconds and then go off once or twice, but that was it. The car was sitting for about 30-45 min or so after driving before I tried this. Is it possible the engine wasn't warm enough? In the normal mode, the CEL does not come on at all. Would a bad 02 sensor necessarily cause the CEL to come on? Is there something I missed when trying this? I suppose the next step will be to check the continuity in the wire from the 02 sensor to the ECU.

I just bought my '92 240SX with 120k miles on it; I have no idea when/if the 02 sensor was ever replaced. I've been noticing a big difference in fuel mileage, at least going by the gas gauge on my second tank. I want to just not trust the gauge, but it still bothers me. Thanks everyone.

[vancouverbc]

I'm working on the same thing right now. When you get into mode 2 by turning the screw(before turning engine on) do you get the five long flashes and 5 short flashes indicating all is well? I dont have to warm my car up too much before doing the O2 test. As long as your rpms are up close to 2000, you should be getting a blinking light. alternting between rich and lean.

I've been told that this test is not definitive. YOu need to get a volt meter and test the O2 sensor. Not sure how to do that.

Dont forget that the O2 sensor does nothing under 2000 rpm.

My cel light in dash(orange on far left) does not come on when i have codes in the ecu. The cel light does come on in mode 2 and blinks out the codes in unison with light on ecu.

A faulty o2 sensor does not necessarily thow a code.