The invention provides a method for controlling an internal combustion engine system (1) comprising a combustor (3) arranged to receive air and fuel, and combust the received air and fuel, an expander(6) arranged to expand exhaust gases from the combustion in the combustor (3) and to extract energy from the expanded exhaust gases, and a communication valve (304) arranged to control a communication between the combustor (3) and the expander (6), the method comprising determining (S3) during operation of the engine system whether there is a pressure difference across said communication valve (304).