If your vehicle rapidly closes in on the vehicle ahead because the vehicle applies the brakes suddenly while you are traveling in headway control, the warning sound activates and the brake warning is indicated in the display. Always verify the safety of the surrounding area and depress the brake pedal while keeping a safer distance from the vehicle ahead.
Additionally, always keep a safer distance from the vehicles behind you.

Mazda Radar Cruise Control (MRCC) Display Indication
Setting the SystemMazda 6 Owners Manual: Closing the Hood
1. Check under the hood area to make certain all filler caps are in place and
all loose items (e.g. tools, oil containers, etc.) have been removed.
2. Lift the hood, grasp the padded area on the support rod, and secure the support
rod in the clip. Verify that the support rod is secured in the c ...
Mazda 6 Owners Manual: Radar Sensors (Rear) (Some models)
Your vehicle is equipped with radar sensors (rear). The following systems also
use the radar sensors (rear).
Blind Spot Monitoring system (BSM)
Rear Cross Traffic Alert (RCTA)
The radar sensors (rear) function by detecting the radio waves reflected off
a vehicle approaching from the rea ...