I dont remember what it stands for Pneumatic Something. It might be called something else for the XF but it's located in the same spot as the slk320. In the trunk under the mat and Styrofoam. You have to remove the trim and panels to remove the styrofoam piece.

I'm gonna flip the module upside down like it's mentioned on the MB forum, cause my blinkers aren't blinking again when I lock/unlock with the key.

Apparently, if the module has water damage, it can mess with a number of things like lights, alarms, and locks depending where the water damage on the module is.

PSE - Removal, Refit and Check - Benzworld.org - Mercedes-Benz Discussion Forum