Pre/Post-Cat Oxygen Sensor, BMW M52/S52 - E36, E39, Z3, MZ3

This is the O2 sensor for either before or after the catalytic converter on 1996-1999 E36 323i/328i, E36 M3 3.2, E39 528i (1997-1998), Z3 2.8 (1997-1998), MZ3 S52 (1998-2000). It measures 990mm in length (39 inches). 

The O2 sensors, also known as Lambda probes, on the E36, E39, and Z3 are some of the most important sensors on the M52/S52 engine. As a pre-cat sensor, they tell the engine computer how well the engine is working (note: not how clean it is, that's the post-cat sensor). The pre-cat sensors give the ECU feedback on the engine tuning - if it's running lean or rich - and the ECU makes adjustments based on their data. Each bank of cylinders has its own sensor before and after the catalytic converters (this sensor is the same for both banks). The ECU adjusts fuel injection based on the data so the sensors also affect 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.

As a post-cat sensor, it reads and checks the status of the exhaust after going through the catalytic converter. The engine computer uses this data to verify the cats are working properly. A failed O2 sensor can set several different types of fault codes so it's a good place to start if you have O2 sensor or heater circuit faults. Most cat manufacturers will insist that you have new post-cat O2 sensors when you install new cats.

Signs of an O2 sensor failure include worse fuel economy, lack of torque, and fault codes for the sensor(s). It is a good idea to replace the O2 sensors at regular intervals rather than waiting for a failure. Since their performance degrades over time you may not even notice the loss in performance or economy. Since the complete O2 sensor is part of the emissions system, a bad sensor may not set multiple OBD Readiness flags.

This part number replaces previous BMW part numbers 11 78 1 437 943, 11781427884. Previously a Bosch OEM was available, but has since gone away. Other part numbers referencing this original BMW unit include 13884, F00E261264, 2344789, 1991, 1974, 6PA358066101, 6PA009166461. 

This is a Genuine BMW O2 sensor manufactured by an original supplier to BMW for this part (usually Bosch or NTK). As a Genuine BMW part, it sets the high bar for quality and meets or beats any OE/OEM you may find on the market. All of BMW's original design, fitment, and performance requirements are included and this part is TUV approved. This part has a two year warranty.