NHTSA Complaint #11430207 — 2020 MAZDA MAZDA3

The Mazda Radar Cruise Control (MRCC) system performs poorly (it does not hold a set speed well up and down hill; compared to our 2006 Mazda3), but the safety concern is the forceful, sudden, and not-always-predictable braking the vehicle does even if there is not another vehicle in front of us. It brakes, sometimes, for a vehicle in the right lane (we, in the left), and continues to brake unless we override the system. No problem--except if there may be someone following too closely, it could cause a collision. It seems to be related to the MRCC, as no "Brake!" warning accompanies the unwanted brake application. I've contacted Mazda numerous times; they recommended taking it to the dealer. I have--they can find nothing wrong. All of this seems related to a MRCC update (SSP C5) that was done to smooth the MRCC's operation. It did fix the sudden deceleration and acceleration when following other vehicles, but now is worse in other aspects. I may be wrong, but it all seems to be a software issue, so it's not surprising that the dealer can find "no concerns". As to the date of this incident, it happens nearly every time we take the car on a highway or interstate.