Oxygen Sensor

The oxygen sensor is one of the most important elements of the modern fuel injection systems. A finely tuned fuel injection system with an oxygen sensor can maintain an air/fuel ratio within a close tolerance of .02 percent. Keeping the engine at the stoichiometric level (14.6:1 air/fuel ratio) helps the engine generate the most power with the least amount of emissions.

The oxygen sensor is located in the exhaust system of the engine, and senses the oxygen content of the exhaust gases. The amount of oxygen in the exhaust varies according to the air/fuel ratio of the fuel injection system. The oxygen sensor produces a small voltage signal that is interpreted by the electronic control unit (ECU) of the fuel injection system. The ECU makes constant adjustments in fuel delivery according to the signal generated by the oxygen sensor in order to maintain the optimum air/fuel ratio.

There are a few signs that your oxygen sensor may be failing. In general, it is difficult to diagnose problems with the sensor, unless all of the other components in the fuel injection system have been checked and determined to be operating correctly. Some of the symptoms of a failed oxygen sensor system are:

Irregular idle during warm-up
Irregular idle with warm engine
Engine will not accelerate and backfires
Poor engine performance
Fuel consumption is high
Driving performance is weak
CO concentration at idle is too high or too low
Check Engine light is illuminated

In general, if the oxygen sensor is not working, the car will be running very poorly, and will also be outputting a lot of harmful emissions. On most BMWs, the engine's computer will give you a warning signal that lights up the Check Engine Lamp if the signal received by the computer is out of it's normal range...

In general, it is recommend that we should be replaced this every 30,000 miles...

reference from: http://www.pelicanparts.com/bmw/techarticles/E36-O2_Sensor/E36-O2_Sensor.htm