Do you mean the Check Engine light? You need a code reader to identify the problem, try posting on the regular E36 forum and give a little more details of the issue, maybe you'll have more answers.
"If everything seems under control, you're just not going fast enough"
River City Bimmers Chapter
2005 X3 3.0i
ZPP, Htd seats, Htd strng, Black Sapphire on Terracotta.
1995 ///M3 Coupe
, Lux, MT, Htd seats, Cosmos Black on Black.