Actually, I believe the ECO light means you are getting an instantaneous FE of 29 MPG or greater. Now, that usually happens when 3-cylinders are in use instead of six, but it can happen with all six cylinders firing.

I am quoting this out of my memory of the articles which came out when the HAH was first released, so I may not have the number exactly right. But it is an indication of instant FE more than an absolute indication of when only three cylinders are being used.

Kyle R.