Engine
What is a mass airflow sensor and what symptoms does it cause when it fails?
The mass airflow sensor (MAF) measures how much air enters the engine so the control unit can work out how much fuel to inject and, on diesels, how much EGR to use. When it gets dirty or fails, the engine loses power, stumbles, stalls or, on diesels, puts out black smoke, and codes such as P0101 appear.
Reviewed by Daniel Morales, founder of Reprorace SL, on
How does it work?
It sits in the intake duct, after the air filter. A heated element is cooled by the passing air, and the electronics translate that cooling into air mass.
Some engines have no MAF and calculate the air from manifold pressure; others have both.
Why does it fail?
Dirt or oil on the element (for example, from an oiled air filter), impacts, moisture or damaged connectors.
An air leak between the sensor and the engine makes it measure less air than actually enters: the symptom looks like the MAF, but it is not.
How is it tested?
In live data, airflow is compared with what is expected for that engine and rpm, along with the fuel trims with a hot engine. The right value comes from the manufacturer's service information.
Sometimes cleaning it with a dedicated cleaner is enough, without touching the element; if not, it is replaced.
General guidance only: every manufacturer and model has its own details. Always follow your vehicle's manual and, if in doubt, ask a workshop.
Related
Related trouble codes
- P0100Mass or volume air flow sensor A, circuit: malfunction
- P0101Mass or volume air flow sensor A, circuit: range/performance
- P0102Mass or volume air flow sensor A, circuit: signal low
- P0103Mass or volume air flow sensor A, circuit: signal high
- P0171Mixture too lean (bank 1)
Related symptoms
- Car jerks when accelerating: causes and what to do
- Black smoke from the exhaust: causes and what to do
- Car stalls by itself: causes and what to do
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See what your car is saying
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Frequently asked questions
Can I drive with a faulty MAF?
Many cars go into limp mode and can be moved carefully to a workshop. Do not push the engine.
Does unplugging the MAF test it?
It is an unreliable home test and leaves codes stored; looking at live data is better.
Does a dirty air filter affect the MAF?
It restricts the air and, if it lets dirt or oil through, it can foul the sensor.