All engine control computers need various sensors to gain information about the changing conditions of the vehicle while in operation. During diagnostic procedures, sometimes it is necessary to simulate a sensor to verify proper operation of the ECM. Since ECM sensors consist of three basic types of electrical configurations, it is very simple to duplicate the majority of sensors used in ECM's today.
The three types of sensor designs are:

1. Switch - An off or on voltage change used in position sensing and operating status sensing.
2. Potentiometer - A variable resistance used in most temperature, pressure, and position sensors.
3. Frequency - An off and on switching of a controlled voltage that measures the frequency of a event. Some examples are ignition pulses, camshaft timing, vehicle speed sensors, tire rotation, and air flow measurement.
4. Once you have a basic understanding of what the ECM needs to know to function properly, it becomes very easy to diagnose a sensor problem. Using parts from your local electronics supply store, most of the sensors used today can be simulated.