SES 95 SL

It's abnormal for there to be no code set but to have the Service Engine Soon light coming on. There are a few cases where that could happen, though, like if the engine speed dropped down to near stall, or if the ECM stopped receiving ignition reference pulses (but then the engine should stop receiving fuel and stall in that case). If it just comes on with the engine running and no codes are set, however, I would suspect either a problem with the power to the ECM or the ECM is shot.