Two problems related to engine shut off without warning have been reported for the 2015 Audi A8. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2015 Audi A8 based on all problems reported for the 2015 A8.
Engine shut down at highway speed ~65mph while decelerating into toll booth our to turbo failure. Complete engine shut down. Lost power in highway traffic. Dangerously navigated through ezpass lane without power. Hazards on. Dangerously navigated to shoulder, coasting, with no engine power. Came to complete stop on shoulder. Was able to restart motor and drove directly to Audi dealership. Dealership confirmed known turbo failure problem on vehicle model. This is a potentially deadly condition and needs to be federally addressed. Audi has a 2015 supplement to emissions warranty identifying the turbo failures and there is a federal statue to extent this correction to 7yr 70k miles. Regardless, it should be a safety recall.
I was driving down the highway then my engine shutoff, it was very hard to control the car, I was able to pull over. Audi says both turbo had blown, I guess its common.