yeh was going to suggest the oil pressure switch, all so do they have a switch that if a certain grade of oil recomended by holden isn't used it can set the pressure switch or oil level switch off, might be completly wrong there, but i know of some jap cars and european cars having this, it lets you know if the oil is low, but if the wrong vescosity oil is used it will set it off, might be a 10/30 like recomended but the grade off oil might be wrong, i know we have this with the new civic typeR at honda (awesome car buy the way, little pocket rocket, like a smaller hatch version of the s2000

) and i think mercs and bmw's might have this too now, just a thought, but like i said could be completely wrong