My wife just took my 99 ml430 on a road trip and she called and said the cel light came on after about 2 hrs of driving. I told her to check the gas cap and she did, no dice. I did read here that someone stated that a change in octane could trigger the light? My wie did stop and top off the tank with reg unleaded about 3 gallons. I wouldn't think that that would be enough to cause it. I guess I will the codes read when she gets home. Any way to clear the light in the meantime?