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Air Fuel Ratio Sensors (Oxygen Sensors)

Air fuel ratio sensors(early 2000's) are an evolution of conventional oxygen sensors (1980's). An air fuel ratio (A/F) sensor measures oxygen content of the exhaust in a wider range. It looks very similar to the conventional oxygen sensor, but has more wires.

A Toyota corolla air fuel ratio sensor

The air fuel ratio sensor is installed in the exhaust manifold or in the front exhaust pipe, before the catalytic converter. The job of the air fuel ratio sensor is to measure the oxygen content in the exhaust and provide feedback to the engine computer (PCM). Based on air fuel ratio sensor signal, the computer adjusts the air to fuel ratio to keep it at the optimum level.

Difference between oxygen sensors and air fuel ratio sensors

Air fuel ratio sensor problems
Often a sensor gets contaminated or simply fails with age. In some cars, the heating element inside the sensor fails causing the malfunction.
In some cars, a sensor wiring may get shorted out after rubbing against metal parts due to corrosion of the wire coverings. It is good to look at the wiring and connector when fixing problems with your sensors.

When the engine computer detects that the air fuel ratio sensor signal is out of expected range it illuminates the check engine light. Most common OBDII trouble codes related to an air fuel ratio sensor are P0131, P0134, P0135, P0133, P0031 and P1135. You can easily get more details using a scan tool.

In some cars you may notice a drop in the fuel economy or some minor driveability issues.

A Bosch air fuel ratio sensor

Bank 1 or Bank 2
In a car, an air fuel ratio sensor is designated as Sensor 1 (upstream, before the catalytic converter), Bank 1 or Bank 2. A rear (downstream sensor, after the catalytic converter) is always Sensor 2. The term Bank refers to a row of cylinders. In several inline 4-cylinder engines there is only one bank, Bank 1.
 Different manufacturers designate banks differently according to their engine configurations, number of cylinders etc. To know for sure, check the model specific service manual. Download one if you ain't got a copy.

Air fuel ratio sensor replacement
Always use an OEM sensor (fit for fit) when replacing a failed sensor. Do not "work another one put". It's inputs are important in engine management. Get a new one if possible.
Due to years of heat and corrosion, you must be careful when taking out the sensor. Some WD40 would really help.

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Email; vverteautosevcs@gmail.com
Phone; 09137103730



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