Technician Handbook ! 673 Electronic & Computer Controlled Systems The Oscilloscope An oscilloscope’s basic function is to display a rapidly changing voltage signal as a graph over time. Oscilloscopes have long been used to analyze engine ignition and fuel systems where signal frequencies are related to engine RPM. With the introduction of automotive ECUs and multiplex circuits, oscilloscopes have now become important tools in diagnosing body electrical systems as well. 34 Technical Training