The ECON button turns the ECON mode on and off.
The ECON mode helps you improve your fuel economy by adjusting the performance of the engine, transmission, heating system*/climate control system*, and cruise control*.
Honda Civic Owners Manual. To Set the Vehicle Speed
When driving at 25 mph (40 km/h) or above: Take your foot off the pedal and
press the -/SET button when you reach the desired speed. The moment you release
the button, the set speed is fixed, and ACC with LSF begins.
When driving slower than 25 mph (40 km/h): If the vehicle is moving and th ...