I added Millers diesel additive to my W203 yesterday and drove 25 miles with no problems. From start up today and all day the engine diagnostic light remains on. The car continues to run perfectly. Checked under the bonnet and everything seems fine. Can this be attributed to the diesel additive or is it simple coincidence? Should I wait till this tank of fuel has been used? Should I get the codes read? There are no malfunctions shown. Do I need to get the codes read to clear this warning light? Any help appreciated.