Oxygen Sensors On Vehicle (WS6)

Oxygen Sensor On Vehicle

The oxygen sensor was located in the exhaust piping after the exhaust manifold before the catalytic converter. This oxygen sensor has 4 wires. This is a heated type Zirconium switching sensor. The wires were:

white - heater supply

black - signal

grey  - sensor ground

white with black strip - heater ground.

I back probed the signal wire on the oxygen sensor and connected the oscilloscope.

I started the engine and let it warm up 4 a bit to enter closed looped mode to see a cycling pattern. I Reved it to 2500RPM for about a minute and it went to closed loop and i could see it cycling.

The voltage went up to 0.9v highest and lowest went down to 0.2v. The average voltage is 0.5v.There was 15 cross counts in 10 seconds. Cross count are voltage high to low or low to high.The signal would not cycle properly if the sensor had a problem wit it. The pattern will be different.

Then with the engine heated up and the oxygen sensor in closed loop we recorded the pattern at idle.

The voltage goes up to 0.7v highest and lowest goes down to 0.2v.The average voltage is 0.35v. At idle cross counts decreased to 7 at 10seconds. The highest voltage is also low then at 2500 rpm because the mixture is leaner at idle than at 2500 RPM. The cross counts also decreased at idle because the revs are lower at idle so the emissions are lower so the oxygen sensor reads slower and then sends out signals slower therefore the cycle is slower.If the signal is not cycling normally there is a problem with the sensor due to contamination  or damage.

Then we made the oxygen sensor go rich by acceleration at short periods.

The signal went high to 0.9v showing a rich mixture.If the signal didn't go high the ecu would not know that the mixture is rich so  would richen the mixture more as it knows there is more air entering the engine. The ecu will think that there is more oxygen in the exhaust so it will richen the mixture more and do more adjustments. This would lead to high fuel consumption and high hydro carbons and unburnt fuel coming out of the exhaust.




We then make the oxygen sensor go lean by doing sudden deceleration. We ran the engine to about 3000RPM for a bit and then let the RPM drop suddenly.

The voltage drops down to 0.2v telling the mixture is lean. If the signal is not going low normally then there is a problem. The signal will be telling the ecu that the fuel mixture is still rich   and then the ecu will make the mixture more leaner. which will cause problems when the problem when the engine decelerates. 


We then measured the response time of the sensor to  know that the  sensor can quickly respond to changes in the exhaust gas. We did a sudden acceleration and recoreded the pattern and then looked at how quick it went from lean to rich. My time was set to 100ms per division.

It took 120ms to go from lean to rich and is within specifications. The sensor is working properly and is quick enough to respond to changes in the exhaust gas.


I conclude that the oxygen sensor is in good condition as the outputs are correct when we made a rich and lean condition. It also cycles correctly in closed loop. 0.2v for a lean mixture and 0.9 for a rich mixture. Also the response time is within specifications.

Zirconium have 2 electrodes which provide an output voltage corresponding in relation to the amount oxygen in the exhaust and amount of oxygen in the atmosphere. The inside of the measuring tube is connected to the atmosphere and the outside of the measuring tube where the exhaust gases travel. If more oxygen in the exhaust the voltage is low that is 0.2v and less oxygen in the exhaust giving a high voltage that is 0.9v. Thats how we get 0.2 to be a lean mixture and 0.9 to be a rich mixture.