One problem related to engine belts and pulleys has been reported for the 2009 BMW X5. The most recently reported issues are listed below.
Vehicle is subject to recall 12v550000 due to idler pulley bolt which can break, causing accessory drive bet to dislodge and loss of power steering, alternator, etc. This vehicle's idler pulley and bolt were replaced as part of the recall 2. 5 years and 35,000 miles ago, but experienced the exact same failure, again, last month. BMW USA and the local dealer were contacted, both refused to fix the issue, stating that the repair is only valid for two years. The new idler pulley bolt that was installed sheared off at its mounting point, just as the original bolt that was subject to recall did. It is clear that the replacement bolt is subject to the same failure as the original - worse, as this failure occurred in under 3 years and 40,000 miles, it appears that the "fix" is worse and more dangerous than the originally recalled part. In my vehicle, the pulley bolt snapped while the vehicle was being driven on a city street, causing a "bang" noise and the complete loss of power steering.