It's got nothing to do with your vehicle warranty being voided, ie the transmission/radio/back up camera/ etc warranty.

However, if your modification causes any problems with vibration, suspension, etc, then that has nothing to do with warranty, it is simply your risk. And by modifying the vehicle, you create a 'grey area' whereby your dealer may believe that a specific problem is related to your modifications, and you do not. Even if you are right, it can cost you time and money until it is resolved.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue