Problem ,Motor lamp in continuous operation

With my swaplommi BJ1998 2l16v the motor lamp lights up ! So as soon as I turn on the ignition the lamp lights up , this does not run out at the start of the engine . But the engine runs without any problems whether in the stationary gas or under full load no problems detect diagnostic device reports no errors anyone an idea ?? So I already thought about the engine control unit or am I there on the wood way ? For a quick help I would be very grateful because tomorrow the engine in my other and it wouldn’t be bad to check that in advance, because with the engine you can get better at everything.