That is disappointing. On a number of levels. Either they didn't reset the computer so it reflected their previous transfer case oil change, or they just rail that line off to everyone who comes in with a 4x4 BMW.

I'd take it to another shop at this point though. Someone with a more in depth diagnostic setup. P0015 could be vanos, cam sensor, etc. I'm not as familiar with the N series of engines as we have an M54 powered mtech x3 but a better scan would probably help point you in a better direction.

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2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)