If memory serves me, Seafoam is mostly tolulene, with diesel, and white gas.
It can work great as a carbon blaster when drowning out a warm motor and letting it set for thirty minutes to overnight ( it will kill lots of mosquitoes when restarted ). If you want to run it though a tank of fuel, add it when the tank is a quarter low or less and drive it a few miles before filling up the rest of the tank.
Won't hurt anything, usually helps.
As to the check engine lights, sensors, etc. If the light is on, chances are you are not getting as good of fuel mileage as you could, especially O2 sensors.
