Oxygen Sensor And What It Does
Oxygen Sensors measure the amount of oxygen in the exhaust gases and send a signal to the Engine Control Unit (ECU). The ECU monitors the signal and accordingly adjusts the amount of fuel entering the engine, keeping the air-fuel ratio closer to stoichiometric ratio. Thus, an Oxygen Sensor optimizes the performance and fuel efficiency and minimizes emissions.
High oxygen content in the exhaust gas indicates a lean mixture which affects performance and causes problems like knocking, misfire and may also damage the engine. Low oxygen content indicates a rich mixture which causes excess emissions and reduces the fuel economy.
How many Oxygen Sensors are there in my vehicle and where they are located?
The number of oxygen sensor depends on the car make, model and mainly on the size and type of the engine. It also depends on the type of the OBD sensor: OBD-I or OBD-II.
In most cases, there are two oxygen sensors in a four cylinder engine. One is located on the exhaust manifold before the catalytic converter and another is located after the catalytic converter on the exhaust pipe. In V6 or V8 engines there are four oxygen sensors, two O2 sensors are located before catalytic converter on each cylinder bank and other two O2 sensors are located after catalytic converter on respective banks.
How Does the Oxygen Sensor Work?
An Oxygen sensor is installed in such a way that one of its surfaces is in contact with the exhaust gas flow and another surface with the outside air. Oxygen sensors do not measure the concentration of the oxygen gas in the exhaust gas, but measure the difference between the amount of oxygen in the exhaust and in outside air.
Based on the oxygen quantity in exhaust gases, voltage signals are provided constantly to the ECU so that it can maintain a stoichiometric air fuel ratio by regulating the fuel injection.
What are Upstream Oxygen Sensors and Downstream Oxygen Sensors?
The upstream oxygen sensor is located right before the catalytic converter. It is installed in the exhaust manifold or in the exhaust pipe near the engine. The role of the upstream oxygen sensor is to optimize the air-fuel ratio entering the engine. There can be one or two oxygen sensors depending on the number of cylinders.
Upstream monitors the oxygen gas in the exhaust gas and provides a signal to the ECU whether the mixture is weak or rich. When there is a high level of oxygen in the exhaust gas, ECU assumes that the air-fuel mixture is lean - so it adds more fuel to the engine. And when there is low oxygen in the in the exhaust, the ECU assumes that the air-fuel mixture is rich and it reduces the fuel supply accordingly.
The downstream oxygen sensor is located in the exhaust pipe after the catalytic converter. The role of the downstream oxygen sensor is to monitor the working and efficiency of the catalytic converter. There may be one or two oxygen sensors depending on the number of cylinders.
The ECU compares the signal from upstream and downstream sensors. If the catalytic convertor is working properly, the amount of oxygen after the catalytic converter should be near to the specified constant value.
If the signal from the downstream sensor varies from the constant value, this tells you that the catalytic converter is not working properly. Hence, the ECU switch on the ‘CHECK ENGINE’ light on the dash.
Why and How Often should I change my Oxygen Sensor?
Oxygen sensors play an important role in both fuel efficiency and engine performance. If Oxygen Sensors are not performing well, it leads to lowered performance of the engine and poor fuel efficiency which ultimately decreases your vehicle's driveability. Hence, it is of utmost importance to keep the Oxygen Sensors up to the mark for the longevity of your vehicle and to receive efficient performance from it.
Every vehicle manufacturer has different recommendations on how often the oxygen sensor should be changed. It is specified at the beginning in terms of mileage or time period depending upon expected day to day use of the vehicle. However, it is strongly advised to get it checked at regular intervals as it depends upon gas-containment, as well as local weather.
How do I know that my Oxygen Sensor is not working properly?
There is no particular symptom that indicates malfunctioning of Oxygen Sensors.One case would be drastic decrease of fuel economy or mileage. Also, you need to check your Oxygen Sensors if the engine is not responding quickly or showing less power while running. Other reasons may include engine hesitation, engine stalling, increased exhaust emission, rough idling and engine pinning.
What are possible causes of Oxygen sensors to be damaged?
Your car's Oxygen Sensor can get damaged from the following
■By incorrect use of silicone gasket sealers.
■Oil deposits on the outer surface.
■If the engine runs on a rich air-fuel mixture for a long time
■By natural aging or accident shocks.
We carry oxygen sensors of many brands.