We tested the O² sensor on a Toyota 1ZZ engine. The 1ZZ has a 3-wire O² sensor. The wires represent the following: White = Heater Power, White (Black strip) = Heater Earth, Black = O² Signal Wire.
This is Zirconia switching type sensor. When the back probe was inserted we got this oscilloscope reading:
From a visual inspection of this signal pattern, we can discern that the signal fluctuates from as low as .05v, to .785v. Our Oscilloscope could not give us an average voltage, but with a quick calculation, I came up with an average of around .418v. This signal had 8 cross counts (Cross counts being one fluctuation from high to low, or visa versa).
We then warmed the engine up in order to test the 0² sensor in closed loop mode.
In closed loop, the signal from the 0² should cycle above and below .5v. The result we recieved from the sensor was far from that.
The signal was floating at just over .1v. This is a very undesirable signal. The cross counts were unmeasurable as there was barely any change in the signal. A sudden acceleration showed a much better resulting signal.
The highest voltage recorded on this signal was .818v. This signifies a rich mixture. This is what is desirable, as the reason we tested with a quick acceleration was to simulate a rich running condition.
Next we recorded the signal after a sudden drop in acceleration, to idle. This was to simulate a lean condition.
The signal did just as i thought it would. As you can see, it has dropped from the good, clear signal, back down to the flat, low signal that it was giving originally.
Apart from at idle, this 0² Sensor gave good readings, leading me to believe that there is a fault in the wiring for the sensor. From the readings i have taken, I believe that this 0² sensor is functioning correctly, and that the circuit for the sensor must be checked for faults.
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