The problem has occurred whenever the donut tire is being used on the vehicle as a temporary replacement for a flat tire - this has occurred on both the two occasions that in which I have had to used them both times on the front tires, once on the left tire and the second occasion, most recent on the left. Apparently, the donut tire because of its smaller diameter causes the car's slip differential system to activate (surmised by the icon I see on the dash when this occurs), often for periods of half the driving time - what then happens is that there is a total loss of engine power to the drive chain, the car cannot accelerate or even maintain speed - it essentially coasts or slows. This occurs even when/if the accelerator pedal is depressed to try to feed power to the wheels - the engine is unresponsive. Intermittently, the power is restored, and then the cycle begins again. Although I have not had an accident due to this loss of vehicle control, I consider myself lucky not to have. Use of a donut tire is the only option open to temporarily replacing a flat tire. I think that this system's response to use of the donut tire (which is manufacturer's supplied) is a defect that is dangerous. A driver must be able to maintain and control vehicle speed to prevent and/or remedy a dangerous situation. [xxx] information redacted pursuant to the Freedom Of Information Act (FOIA), 5 U.S.C. 552(B)(6).

- Bethesda, MD, USA

Cause: Flat tire in the front left or front right of the vehicle. The front left demonstrating the most severe hazard failure: The traction control system engages regularly due to a discrepancy between the spare and normal tire size. Traction control cuts power to the drive wheels and cannot be overridden, causing vehicle to lose speed in non-deterministic manner. Vehicle is not responsive. Condition is worst during the first 40 miles driven on the spare tire but consequently improves due to learning inside the car computer. Unfortunately, vehicle is most dangerous when the driver has the least control over the situation. Correction: None, the manufacturer claims the vehicle is operating as designed.

- San Francisco, CA, USA