Just out of interest where do you get your fuel?
My wife had a Saab diesel and the engine management light would come on periodically, sometimes throw it into limp home mode. Eventually she took it to the garage, the first thing they asked was where do you get your fuel?
Morrisons she answered.
Try somewhere else for a few weeks, see if that cures it. They said.
The only other fuel we have around here is Texaco, so she used that for a few weeks... which turned into months...
Sure enough the light never returned !