oxygen sensor on car

I did the following tests on the 1zz engine.On this engine this sensor was located on the exhaust manifold just when it goes into one pipe.This sensor has 4 wires:
colour                                 use
white                                  signal
white                                  O2 sensor
white                                  ground
black                                 power heater

The sensor I was working with was a zirconia switching sensor.I had to hoock up a oscilloscope to the sensor to get a patern.I did this by back-probeing the signal wire and putting my oscilloscope to it.My first task was to get a pattern at 2500rpm.With this pattern I found that the higher the voltage gets the richer it is.

The voltage goes as high as 0.715v and it goes as low as 0.1v.The average voltage was 0.6v,the oscilloscope had a function to calculate this.This sensor had 3 cross count.One cross count is when it goes from low to high or high to low.

My next task was to get a pattern of the oxygen signal at idle in closed loop.Closed loop is when car is warm and the ECU uses actual information to adjust sensor and not a set map like open loop.

In this one the voltage only went up to 0.2v and went to as low as 0.1v again.0.15 was my average voltage and again it had 3 cross counts.

In the next task I had to make my oxygen sensor go rich and get the pattern.I did this by giving it a quick accelaration.

This gave out a higher voltage of over 0.85v.If this did not give a high voltage the voltage will be changed and will not give a good wave form.

Next thing I had to do was make the oxygen sensor go lean.I did this by running the rpm to 3000 then sudenly dropping the throttle.

The voltage dropped from 0.8v to 0.1v.This shows us the lower the voltage the leaner the car is running.If the voltage is not high the waveform will be bad and wont go down as low as it should.

Next thing I did was measuring the response time I did this by sudenly acceleratin to see how quickly the sensor went from lean to rich.

The voltage went from 0.1v all the way up to 0.8v the bottom is at idleing the goin up is at accelerating and the top is when it is rich.It took the sensor 100ms to go from rich to lean


The zircronia sensor is based on a solid-state elctrochemical fuel cell called the nernst cell.On this system when the voltage is 0.2v this indicates a lean mixture and at 0.8v it indicates a rich mixture.It is most sensitive near stiochmetric point and less sensitive when rich or lean.

this is a good picure of http://www.wikipedia.org/ to show how the sensor works.