A safety critical incident occurred on my new 2019 Mazda 3 hatchback when the vehicle when into "limp" mode while adaptive cruise control was engaged at highway speeds leading to rapid deceleration. The vehicle was towed to the nearest manufacturer service location where a diagnostic was performed. Codes show that communication between the central vehicle processor and multiple sub-processors failed simultaneously. Comments were made by manufacturer service representatives that failure mode is likely different from the recent cylinder deactivation/rocker arm recall. Service representatives were instructed to simply clear the codes and drive the vehicle to attempt to reproduce the failure during which it did not occur. I have attached a sanitized version of the service receipt to this message with the full list of codes. Unfortunately Mazda's representatives were unable to provide any explanation on why this failure occurred or what will be done to prevent it in the future. Engineering analysis will need to be performed to reach an acceptable conclusion. Environmental factors relating to the incident include a very hot outside air temperature, with a reading of 115 deg F from the vehicle's sensor roughly 15 minutes before the incident. The incident also occurred on a very long section of us highway with a consistent, gradual incline. Given that information potential causes are intermittent computer hardware failure in high temperature environments, or a software error in power train control or cruise control causing a communication bus failure. With the age and mileage of the vehicle (336 mi) the potential for this failure occurring is likely present in a large portion of new Mazda vehicles.

- Palmdale, CA, USA