When the PCM is in closed-loop, it receives information about the automobile from sensors (throttle position sensor for example), uses this information to determine what appropriate actions to take (increase injector duty cycle for example), and then makes change to the automobile via actuators (EGR solenoid for example).

An automobile leverages numerous sensors that communicate to the PCM using simple signaling techniques. Likewise, an automobile leverages numerous actuators that are controlled by the PCM using similar simple signaling techniques.

I will discuss common signaling techniques that you might encounter troubleshooting automobiles. With a little knowledge, you will be able to read wiring diagrams and shop manual overviews to understand signals you encounter while diagnosing issues you will encounter.

Before continuing on, I suggest you have familiarity with the following, which can all be accessed via the Electronics page:

• Auto Shop 101.com
• Physics Classroom
• Electronic Concepts
• Sensors
• Testing Concepts