A method for controlling operation of an electronic control unit for use in an internal combustion engine, the electronic control unit being used to control different engine modes, the method including providing a function mode map having a plurality of data map points wherein the function mode map is divided into at least a first type region containing data map points representing mode map output values only of a first mode type and a second type region containing data map points representing mode map output values only of a second mode type; and providing at least one further data map having a plurality of further data map points, each of the further map points representing a further data map output value. The method also includes determining a current mode for an operating point on an operating path within the function mode map in dependence upon first and second engine operating parameters and determining a control function for the electronic control unit based on the current mode of the operating point and at least one further data map output value determined from the at least one further data map.