Pre-Cat Oxygen Sensor, Bosch - E30 325e, E28 535i (87-88) - 11781716156

This pre-cat O2 sensor (located before the catalytic converter) was used on a handful of BMW models, most notably the E30 325e & 325es, but also on a limited range of 80's 5/6/7 series (see list below).

The pre-cat O2 sensor, also known as a Lambda probe and was used on the E30 325e, E28 535i, and 1987 Model E24 635CSi. It is one of the most important sensors on the M20 eta and later M30 engines. The pre-cat sensor tells the engine computer how well the engine is working (note: 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.

Please note: On M30 models (E28 535i, E24 635Csi, E23 735i) this sensor is ONLY for specific years. See list below: 

E28 535i & 535is - 1987-1988 models ONLY. 
E24 635Csi - 1987 model ONLY. 
E23 735i - 1985 & 1986 models ONLY. 

NOT for M30 models not listed above. Please check your M30 fitments carefully (this applies to 535i / 635Csi / 735i only). 

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.