Front and Rear Pre Post Cat O2 Lambda Sensor for B-M-W 3 5 7 Series X3 X5 E36 E38 E39 E46 E53 E60 E61 E65 E83

These are for use on the car. Liked the two post cat downstream sensors as they are 990mm in length, just right. Disliked the two pre cat upstream sensors as they are short 450mm in length. There is no etching of manufacturing part numbers of any kind on them, nothing, completely nothing to use for reference. Also no instructions or warranty in the box, so I'm just hopeful they will last. Update: unfortunately the sensors heater circuit is causing the car's ECU to register a fault right away. The car's CEL check engine light came on within minutes, tried clearing it but came back on startup.