Crankshaft Position Sensor, OEM - E46 M3, MZ3 S54, Z4M (12147830789)

This is an OEM crankshaft position sensor (aka speed sensor or reference sensor) for the S54 engine in the E46 M3, MZ3 S54, and Z4M. This sensor tells the engine computer what position the crankshaft is in to set ignition timing and other settings. If your engine is hard to start and takes too many cranks before it catches, this sensor has likely failed.