FC A Basic Alarms Practice Test

Knowing exactly how much air is entering the engine is essential for metering fuel correctly. The Mass Airflow Sensor provides this by measuring the mass of incoming air as it passes into the intake. It often uses a heated element whose cooling effect changes with air flow; the ECU uses that signal to calculate how much fuel to inject to maintain the desired air-fuel ratio.

The Oxygen Sensor sits in the exhaust and tells the ECU whether combustion was rich or lean, so it can fine-tune fuel after combustion rather than measure how much air is entering. The Throttle Position Sensor indicates how open the throttle is, giving a sense of potential air flow, but it doesn’t measure the actual air entering. The Crankshaft Position Sensor tracks crankshaft position and speed for ignition timing and engine cycles, not air intake.