Engine fail safe light came on and idle is now rough, gas pedal not responding

[MosH]

So before I left for vacation 2 weeks ago I had my coolant resiviour crack in the car wash drive through. Luckily the car did not overheat as I saw the steam coming out and shut her down. I was able to get the part from the BMW dealer 3miles down the rd and replace it on the side of the road.
Today I came back, the truck was dead as a door nail. Battery was compeltely drained. I put her on my charger for about 3hrs on a 10 amp charge and it started right up. I decided to take the truck food shopping, it ran perfect, dead center on the temp gauage. When I pulled into my driveway I revved the engine a few times just to make sure she sounded good and all was clear, then boom, engine fail safe prog....

Any ideas? I decided to disconnect the battery and put the charger on the battery directly on a 2 amp charge which I will leave on overnight. Just in case the low battery was causing any issues.

Will the code clear with the battery disconnected overnight or will I need to bring it somewhere to have it cleared? If the same thing happens tomorrow I am stuck since the truck is not drivable...