Technical Information

Zirconia Oxygen Sensor

Titania Oxygen Sensor

Zirconia Sensors: An important property of the Zirconia element is that it can conduct oxygen ions above a temperature of about 350°C. When the sensor is fitted, the outside of the Zirconia element is exposed to the exhaust gas and the inside is in contact with reference air.

Both sides of the element are coated with a thin layer of platinum that act as electrodes and carry the sensors voltage signal from the Zirconia element to the lead wire. At operating temperature, oxygen ions are able to pass through the element and deposit a charge on the platinum electrode thus generating a voltage signal.

If the AFR is rich, a high signal voltage is generated across the electrodes due to the difference in oxygen concentration present across the two sides of the element. Conversely, if the AFR is lean, a low voltage is generated across the electrodes due to the small difference in oxygen content between exhaust gases and the reference air inside the sensor.

Titania Sensors: The Titania element in these sensors does not produce a voltage like the Zirconia element. The property of the Titania element which allows for the detection of oxygen in the exhaust gas is its electrical resistance. The electrical resistance of the Titania element changes according to the concentration of oxygen in the exhaust gas.

The ECU supplies a voltage to the Titania sensor which depending on the presence, or lack of oxygen in the exhaust gas, will vary its resistance consequently changing the voltage signal returned back to the ECU relating to a lean or rich AFR.

Due to their different properties Titania and Zirconia sensors should not be interchanged under any circumstance.

Visual inspection alone is not usually sufficient to determine if an oxygen sensor is functioning correctly. However, the following are considered mandatory basic checks:

• The lead wire and connector should be checked for damage. Any damage will interfere with the sensor signal. Due to the fragile nature of the element it is possible for the sensor element to be critically damaged internally, despite the lack of physical external damage.
• The sensor body should be checked for dents, which are a sign of mechanical shock that can crack the sensor element.
• The appearance of the sensor's protector tube can give an indication of possible problems.

Below are some examples of damaged sensors and an indication of what might have been the possible cause. The cause should be rectified and the sensor changed to avoid further problems including damage to the catalytic converter.

For the ECU to control the AFR and keep it within tight limits, the oxygen sensor must be working properly. Failed or worn out oxygen sensors cause problems such as poor fuel economy, failed emission tests, failure of the catalytic converter and poor driveability.

Therefore it is important that you can read the signs of a failed or worn oxygen sensor and have the ability to check their performance.

ON CAR TEST: Before you can test the operation of the sensor, you will need an oscilloscope. You should first check that the basic engine set up is to the manufacturers specification, then thoroughly warm up the engine - remember that the sensor will only function once it has reached its operating temperature.

Using an appropriate connecting device, connect the sensor output to your oscilloscope; do not disconnect the sensor from the ECU. Run the engine at approximately 2000 rpm. A properly functioning oxygen sensor will show a rapidly fluctuating output voltage between approximately 0.1 and 1.0 volts. The time taken for the voltage to change from 0.1 V to 1.0 V (referred to as the lean to rich response time) should be about 300 milliseconds. A similar time should be measured when the voltage changes from 1.0 V to 0.1 V (rich to lean response time).

If the sensor output is constant or the response time is too slow the sensor should be changed. It is a good idea to check the oxygen sensor function at every tune up and before submitting cars for emission tests. A slow sensor will affect fuel economy. A new sensor will pay for itself by cutting fuel costs.