OXYGEN SENSOR

THEORY

The oxygen sensor is a Zirconia switching sensor. It is located in the exhaust manifold. It is used to detect the oxygen content of the exhaust gases as they pass from the engine. The amount of oxygen in the exhaust is a measure of the air-fuel ratio of the mixture entering the engine. The oxygen sensor feeds information to the ECU, which then adjusts the fuel injection pulse width at the injectors. This is a continuous process, so the optimum air-fuel ratio is always obtained. The oxygen sensor, also called lambda sensor, is used to provide a closed loop operating system.

PROCESS    

·       First of all I recorded the colours for each of the wires at the sensor side of the connector not the ECU side of the connector.  The following is the use of each wire:-

      I.        A black or blue wire will usually be the O2 sensor signal.

    II.        Grey may be the sensor ground.

  III.        Heater power and ground are often white. But there may be                                            other colours.

Colour: - Use or Purpose

White: - Heater Positive (+)

White: - Heater Negative (-)

Grey: - Signal Negative (-)

Black: - Signal Positive (+)

·       Then I back probed the Oxygen Signal Wire with a pin and connect to an oscilloscope. Then I checked that it was connected to the Oxygen sensor signal. Then I ran the engine and checked that weather I got signal or not, and I got the signal.

·       Then I watched and recorded the Oxygen Signal pattern at 2500 rpm. The engine should be warmed up and enter closed loop so you see a normal cycling pattern. You may have to hold the rpm about 2500 for half a minute to go into closed loop.

The voltage fluctuated between 0.869V and 0.139V. The average voltage was 0.475V.

The number of “Cross Counts” the signal had in 10 seconds (One cross count is when it goes from high to low, or from low to high) were 25 (at 2700 RPM).

When the signal is not cycling normally, the signal does misfires in one cylinder; the cycle will have dips in it.

·       Then I recorded the Oxygen Signal pattern at idle rpm. The engine should be warmed up and enter closed loop so you see a normal cycling pattern. You may have to hold the rpm about 2500 for half a minute to go into closed loop. Then let the RPM come down to idle.

The voltage fluctuated between 0.9V and 0.119V and the average voltage came around to be 0.475V.

It had 10 “CROSS COUNTS”

If the signal is not cycling normally, the signal will have a negative pattern on the graph.

·       Then I made the Oxygen Sensor go rich by accelerating once or twice. (The fuel system should normally make the system go rich when you do a sudden acceleration.) Push on the accelerator quickly but don’t let the rpm go high enough to hurt the engine. The signal should go over 0.85V.

The reading went highest to 1V.

If the signal is not going high normally, the signal will have a very low voltage and it will be lower than 1.0 volt.

·       Then I made the Oxygen Sensor go lean by doing sudden deceleration. Gently run the rpm to about 3000, and let the rpm drop suddenly. The fuel system should make the system go lean on deceleration. The signal should go below 0.2 V

The voltage went 0.015V the lowest

When the signal is not going low normally, the signal will be above zero volts, might be a sluggish oxygen sensor.

REFLECTION

The oxygen sensor is very useful sensor. If the reading of the oxygen sensor would not be appropriate then there would be a problem in the car.