Diagnosing and troubleshooting engine starting problems typically involves inspecting the ignition control module. The ignition control module is used to switch primary current flow for the ignition coil. The control module switches these transistors on and off based on information from a magnetic pulse generator in the distributor. Some conventional electronic ignition systems and all distributorless ignition systems, use a crankshaft position sensor in place of a distributor mounted pulse generator. Crankshaft position sensors and magnetic pulse generators both output an AC voltage signal that corresponds with crankshaft position and engine speed. This signal is also known as an analog signal. Since logic circuits used in ignition modules and engine control modules cannot process analog signals, the signal is changed into a digital signal, by a signal converter inside the ignition control module. A digital signal is basically read as an on/off signal by the control module.