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: Contact Authorized Mazda Dealer and Have Vehicle Inspected
If any of the following warning lights or the indicator light turns on/flashes,
the system may have a malfunction. Contact an Authorized Mazda Dealer to have your
vehicle inspected.
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Mazda 6 Owners Manual: Constant Monitoring
The following components of the air bag systems are monitored by a diagnostic
system:
Crash sensors, and diagnostic module (SAS unit),
Front air bag sensors
Air bag modules
Side crash sensors
Air bag/Front seat belt pretensioner system warning light
Front seat belt pretensioners
Re ...