One problem related to adaptive cruise control has been reported for the 2011 Porsche Cayenne. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2011 Porsche Cayenne based on all problems reported for the 2011 Cayenne.
At highway speeds, randomly a serious unsafe to operate 'service necessary' warning appears on the instrument panel and the cruise control malfunctions; abruptly shutting off. With the service necessary warning indicated, the vehicle is unsafe to operate. This unsafe vehicle is not drive-able with cruise control. Error will go away on its own. This breakdown appears to be known to Porsche based on what I have seen on internet community sites.