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: Instrument cluster inspection
Speedometer
Using the input/output check mode
Inspect the speedometer by setting it in the input/output check mode DTC 12.
Using a speedometer tester
1. Adjust the tire air pressure to the specification.
2. Using a speedometer tester, verify that the speedometer indication is
within the allow ...
Mazda 6 Owners Manual: No.8 no cool air
When performing an asterisked (*) troubleshooting inspection, shake the
wiring harness and connectors while performing the inspection to discover
whether poor contact points are the cause of any intermittent malfunctions.
If there is a problem, check to make sure connectors, terminals ...