Did they actually tell you which codes the ECU stored when the light was triggered? Or are they saying that a ground track in the ECU was the cause (very unlikely I would think). If the light is again I would get them (or someone else with an OBD scanner) to scan it and tell you which codes are stored now. I've been tripping and resetting codes over the weekend and the system even shows codes that are pending. This is the whole point of OBD it is there to tell the techs what the problem is.