Its behind/below the Y-pipe of the airboxes, directly below the throttle body. Check this video for more clarification: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ALMnplyTFX8.html
To be honest, I dont know. I replaced because of preventative maintenance. They aren't that expensive, so makes sense to do so. In the end I bought another one at the Mercedes dealer