Oxygen sensor locations
 

I have a 97 328i sedan m52 block,,,I keep getting a ... check engine light code 'oxygen sensor slow response'
,,,,,,,Bank1,Sensor1.. on my OBD2 reader,,where is this sensor located on the engine?...and does anyone know what the BMW part # is..Thanks John

Your four O2 sensors are on the exhaust.

Sensor 1 means pre-cat which is on the manifold and Bank 1 means the front most manifold.

Clear the code and see if it returns. You "can" swap sensors to make sure it is the sensor if the symptom follows but they can be hard to remove so replacement might be a better option.