Pre-Cat Oxygen Sensor, Bosch - E30 E24 E28 - 11781286638

This pre-cat O2 sensor is located before the catalytic converter, measures 520mm in length and has a 3 pol (3 pin) connector. Be aware there were sometimes more than one oxygen sensor that might be used, so check your fitment carefully before ordering. 

This sensor was often found on the E30 325e & 325es (2.7 liter eta engine), the E28 535i (1985 and 1986), E24 635CSi (1985-1986), and E23 735i (1985-1986). 

Please note: On 5/6/7 series this sensor is NOT for cars after the 1986 model year. BMW changed the pre-cat O2 sensor on these 5/6/7 series models after 1986, and this is the earlier style / fitment. 

A pre-cat O2 sensor is also known as a Lambda probe, and is one of the most important sensors on the M20 and M30 engines. The pre-cat oxygen sensor tells the engine computer how well the engine is working (but NOT how clean the emissions are). The pre-cat sensor gives the ECU feedback on the engine tuning - if it's running lean or rich - and the ECU makes adjustments based on its data. The ECU adjusts fuel injection based on the data so the sensor also affects fuel economy in addition to performance. An integrated heater circuit helps prolong the life of the sensor but can also fail and give a check engine light.

Signs of an O2 sensor failure include worse fuel economy, lack of torque, hard starting, and fault codes for the sensor(s). It is a good idea to replace the O2 sensor at regular intervals rather than waiting for a failure. Since the performance degrades over time you may not even notice the loss in performance or economy.

This is a genuine Bosch E30/E28/E24 O2 sensor. Bosch is the original supplier to BMW for oxygen sensors, as well as the original inventor of the O2 sensor.