Originally Posted by josiahg52

Valeo 220A and the same part number for my 2011 35d.

The decoupler is a overrunning or clutched pulley that diesels should have on their alternators. INA, BMWDieselParts, and Litens all make the correct pulley. I plan to use a Litens when I rebuild mine. These type of pulleys require a tool, not exactly a tool, but a technique to remove the pulley. Basically a socket with wrench flats and a hole to pass the Torx bit through.