HONDA 2015 Civic Si Sedan - Owner's Manual - Manual (Page 326)

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uu When Driving u ECON Button *
Driving
ECON Button *
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 and cooling system
* /climate
control system * , and cruise control * .
*
* Not available on all models