Glossary
mass airflow sensor
A mass airflow sensor sits in the intake and measures how much air is on its way into the engine, so the computer can add the matching amount of fuel.
A mass airflow sensor measures the air going in. It sits in the intake tract ahead of the engine, where every bit of air the engine will burn has to pass it, and it reports the mass of that air to the computer. The reason the engine needs the number is chemistry: burning fuel takes air in a fixed proportion, so more air needs more fuel. The computer reads the airflow and adds the matching amount, which is what keeps the mixture right across idle, cruise and hard acceleration.
The measurement itself is usually made by a heated wire or film in the airstream: flowing air carries heat away, and the current needed to hold the element at a constant temperature tracks the mass of air passing it. That is also why a dirty element reads low — the engine then runs lean and misfires, which is the fault most likely to be described in a question.
Older cars did the same job with a manifold absolute pressure sensor, which infers airflow from intake vacuum instead of measuring it. The question names whichever the car has, and the job is the same one: the air on its way in.
Taught in
Related terms
- oxygen sensor — An oxygen sensor sits in the exhaust and measures how much oxygen is left over after the burn, so the computer can tell whether the last mixture ran rich or lean and correct the next one.
- turbocharger — A turbocharger uses the engine's exhaust to spin a turbine that drives a compressor, forcing more air into the cylinders so more fuel can be burned and more power made from the same engine.
Source: Official ASVAB — subtest descriptions (what each subtest asks) and the CAT-ASVAB scored-question counts (accessed 2026-09)