Where is the metering valve physically located? Is it something we can easily replace ourselves, post-warranty?

__________________

2011 BMW 335d, Space Grey/Black, Sport, Premium, Cold Weather, Convenience, Nav, Harman Kardon/Sat, iPod
2010 Audi A4 2.0 Quattro P+ 6MT (Wife's car)
2004 BMW R1150RA