jimh425 wrote:
Sorry, the symbol was actually Service Engine Soon according to this page. https://owner.ford.com/how-tos/vehicle-features/dashboard-instrument-cluster/warning-lamps-and-indicators.html
So it is a check enging light. Unless you read the code it could have been any number of things. They will clear after so many key cycles or time if the event is no longer present. I would say coincidence on the additive. In any case some sensor was out of range to both trip the light and give you reduced power. A check engine light in itself does not always result in reduced power.