Testing the Oxygen (O2) Sensor

[Soul Shinobi]

After expressing concern for strange idle condition (bouncing between 500 and 1000 RPM on warm starts) someone recomended testing my O2 sensor, so I did.

I used the ever useful B10 ECU scan tool to get voltage readings.

My Haynes manual says the O2 sensor should read 0.10-0.20 volts (meaning it's running in open loop mode) when the car starts cold, and should then read between 0.10 (lean) and 0.90 (rich) after just a few minutes when the exhaust has warmed up. Also it states that if the sensor takes a long time to exit open loop mode or it doesn't exit open loop mode, then replace it.

Okay, so according to my ECU my O2 sensor read as such:

0.30 then 0.26 volts (could be increased when I revved, but that shouldn't count I don't think). Then after a few minutes it started reading between 0.10 and 0.80 (never went into 0.90 territory). Sometimes it would stay steady at 0.4-0.5 for just a bit but would then fluctuate in the acceptable range. When revving the voltage would change rapidly, and if I held the engine at any RPM the voltage would fluctuate. Just once it dipped to 0.04 after I took my foot off the pedal.

Of course I observed many more things than the Haynes manual covers, so I thought I'd show this all to you for evaluation, I don't know a whole lot about cars yet and couldn't guess if my car's deviations from the ideal condition are acceptable, or if they mean something specific.

[Legacy777]

The O2 sensor voltage should bounce around between 0.1 v and 0.9 v

If it's not moving much or very slowly, then it should probably be replaced.

[grippingdrifting]

What is proper behavior for the O2 sensor voltage?

When I used the scan tool my voltage was changing rapidly. It was hard to determine what the exact voltage was but I noticed values between .04v and .93v.

[Soul Shinobi]

That range seems okay, but I don't know if it's supposed to dip below 0.1v; mine does but I think mine might be on its last legs. It should be moving rapidly, like Legacy777 said.

If it's not moving much or very slowly, then it should probably be replaced.