Not only will you use the steering wheel controls, but you will also lose the On Board Computer info as well, including the ability to set the clock. Removing the stock radio/head unit is not a great idea. I don't know what that Pioneer unit is, so this post might be irrelevant.

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-'13 E93 M3 Cab, Interlagos Blue, Carbon Black leather, DCT, all options, and fun, endless fun!
-'13 X5 35i M-Sport, Carbon Black & Cinnamon, Dinan Stage 2!
-'15 Toyota Sienna Limited Premium AWD, Silver & Grey, Nav & BluRay, and less lame than the 2011 it replaced
-'07 Mini Cab S, Laser Blue, 6sp, endless fun that ended (sold)
-'04 X5 4.4i, loaded, loved, modded and sold