Pre-Cat Oxygen Sensor, Bosch - E30 325i, E31 850CSi (11781720860)
E30 325i: 1988-1992. Genuine Bosch O2 sensor to keep your emissions system running smoothly
E30 325i, E31 850CSi pre-cat O2 sensor (located before the catalytic converter).
The pre-cat O2 sensor, also known as a Lambda probe, on the 325i is one of the most important sensors on the M20 and S70/1 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.
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 325i O2 sensor. Bosch is the original supplier to BMW for oxygen sensors, as well as the original inventor of the O2 sensor. 850CSi takes two sensors.
E30 (84-91) > 325i
E30 (84-91) > 325is
E30 (84-91) > 325ix
E31 (91-97) > 850CSi