What is an oxygen sensor and what does it do?
An oxygen sensor measures the amount of oxygen in the engine’s exhaust gas. In combination with the vehicle’s catalytic converter, the oxygen sensor controls the exhaust treatment, and, with the engine control unit (ECU), the oxygen sensor ensures optimal air-fuel mixture composition to ensure overall smooth, powerful, clean and economical engine performance.
A vehicle’s catalytic converter will only function correctly if the air-fuel mixture composition is correct as it is dependent on the amount of oxygen present in the exhaust. The oxygen sensor is the crucial component and feedback mechanism in the engine management system.
Properly functioning Bosch oxygen sensors will help: Reduce fuel consumption. Avoid expensive catalytic converter failures. Reduce exhaust emissions. Improve driving performance. There are two main types of oxygen sensors, “switching” and “wideband”. A “switching” sensor allows the ECU to determine if the exhaust is rich or lean and can be used in both pre- catalyst and post-catalyst positions. A “wideband” sensor allows the ECU to determine how rich or how lean the mixture is, and used only in the precatalyst position.
The signal from the pre-catalyst oxygen sensor is primarily responsible for air-fuel mixture adjustments, while the post-catalyst oxygen sensor signal monitors the performance of the catalytic converter and the amount of oxygen being absorbed during its operation.
Oxygen sensors have evolved over time, and are available as simple single and unheated, two-wire unheated, three and four-wire heated switching sensors and now five-wire wide band sensors.
Heated sensors allow the sensor to reach operating temperatures more quickly providing a quicker response and more accurate data to the ECU, leading to lower emissions. Heated sensors also have an extended service life due to lower sensor deterioration from heat stress.
Bosch offers a range of direct fit oxygen sensors and a universal range. The direct fit type is designed to be a
simple “plug-and-play” type similar to the original equipment item fitted on the vehicle. The universal type sensor is an alternative option in cases where a direct fit option is not available. The universal sensor requires some additional labour for installation.
However, in combination the direct fit and universal oxygen sensor provide a good range to the market to cover the majority of applications.
When should an oxygen sensor be checked and or replaced?
While there are many factors that contribute to premature oxygen sensor failure, it is important to understand that an oxygen sensor is a wear part with a specific service life not unlike a platinum spark plug.
An oxygen sensor should have a service life ranging from 50,000km to 160,000km, depending on its design, but this can be dramatically reduced by abnormal operating conditions, including overheating of the sensor, chemical contamination and impact damage.
Over time, and as the oxygen sensor deteriorates, the output from the sensor slows down giving the impression the engine is running lean with the fuel management system overcompensating, thus leading to increases in fuel consumption.
It is good practise to check oxygen sensor function at every major service.
Tips and precautions
Bosch oxygen sensors are supplied with special high temperature resistant grease for ease of installation. On fitment, oxygen sensors should be first tightened by hand until the sealing washer is in contact with the exhaust mounting boss before using an appropriate spanner tightened to 40 – 60 Nm.
Wideband sensors must not be disconnected while operating as this can lead to premature sensor failure.
The sensor heater supply must never be connected directly to battery supply. The sensors require ECU control of the heater power to avoid thermal-shock, especially if condensation may be present. Do not expose hot sensors to water as thermal shock can damage the sensor.
Do not drop sensors during installation as cracks in the sensor element can occur. Do not use any lubricants or sealants that contain silicone.
Cleaning agents, grease, or repellents must not be used on or near the connecting plug. The sensor must not be exposed to vehicle under body sealants, wax, tar or rust prevention products. Cover sensor if undertaking body repairs.
Ensure the sensor cable has free movement to allow for movement in the exhaust system. For further information on Bosch oxygen sensors please contact 0800 452 896 or visit www.boschautoparts.co.nz