1999 Chevy Blazer engine management light

Engine Mechanical problem
1999 Chevy Blazer 6 cyl Four Wheel Drive Automatic

1999 chevy blazer 4.3 v6 52000 miles, my engine management light has come on for no apparent reason, no other symptoms, running temp is normal, oil pressure good, the car runs perfect, any ideas thanks for your time, Dean, London England oh yeh I actually run this vehicle on LPG, Liquid petrolium gas, I have done for the past three years $12 a gallon over here!