2012 Dodge Ram 1500, The image of an engine on dashboard and ECO appears on the odometor. Why?

Read your owners manual but ECO probably refers to economy mode. You may need a new gas cap or maybe there is another problem with your EVAP system.

I have a 2014 Dodge Ram 1500 4x4 5.7 Hemi. The ECO showing on the dash is showing the system that cuts out cylinders to save fuel is operating normally. The ECO light will come on under low speed or very light throttle operation. If the check engine light is on the ECO mode is deactivated. The ECO mode will also not function when trailer tow mode is selected. I have had numerous problems with the gas cap code on my truck. I even tried a replacement gas car from O'reilly Auto Parts and it did not help the issue. It's funny, but the issue went away when I had new tires installed on my truck. Neither me or the mechanic shop have any idea why changing tires caused the loose fuel cap indication to go off. If you try a replacement gas cap, get one from Dodge as they are better than the aftermarket. Closely inspect the O'ring on your gas cap for small cracks. If the O'ring is cracked then you need a new gas cap. Do some reading on the Eco mode (MDS system) at the link. https://en.wikipedia.org/wiki/Multi-Displacement_System

unhook positive cable from battery Leave off for 20 min then hook up again.It will reset the computer and be good again,