CEC Introduction: Operation: Sensors

The computer gets its information from a network of sensors. Most are simple sending units just like an oil pressure switch or fuel level gauge. Either the sensor is off/on or it gives the computer a variable resistance reading. Many systems use existing engine sensors, while some systems have specialized sensors that provide input on engine "knocking", atmospheric pressure or outside air temperature.

The control unit checks sensor inputs constantly and makes its decisions based on both pre-programmed input and the sensor readings. Common sensor inputs include:

• Air/Fuel Ratio (from exhaust gas oxygen sensor)
• Engine Speed (from distributor or crankshaft sensor)
• Engine Temperature (from oil or coolant sensors)
• Engine Load (from throttle position or vacuum level sensors)

Other sensors are used by some systems to provide additional information. These may include:

• Intake Air Temperature
• Intake Air Volume
• Barometric/Manifold Pressure
• Vehicle Speed
• Fuel Temperature and Pressure
• Detonation
• Transmission Gear

Two different systems may require the same kind of information, but get it from different sensors. For example, one of Ford's MCU systems uses an idle switch to tell the computer when the throttle is against the idle stop. Another MCU system uses a vacuum sensor to provide the same information. Despite the variety of sensors, computers make their decisions based on the same kind of inputs.