Mass Air Flow (MAF) Sensor
What it is
The mass air flow sensor sits in the intake duct between the air filter and the throttle body. A fine heated wire or film measures exactly how much air is entering the engine.
What it does
It tells the engine computer the mass of incoming air so the computer can add the correct amount of fuel. A dirty or failing MAF under- or over-reports airflow, causing lean or rich running, hesitation and stalling — and it is one of the most common causes of lean codes like P0171.
Symptoms of failure
- P0171/P0174 lean codes or P0101–P0103 MAF codes
- Hesitation or stumble on acceleration
- Rough idle or stalling
- Hard starting
- Poor fuel economy
Common fault codes
Which vehicles need it
Most fuel-injected petrol engines. Hot-wire and hot-film MAFs are common on Toyota, Ford, VW/Audi, Nissan and GM.
Replacement cost
| DIY (part only) | $20–$120 |
|---|---|
| At a shop (parts + labor) | $120–$300 |
| Replacement interval | No fixed interval — clean it whenever you change the air filter; replace when it sets a code that cleaning does not fix. |
| DIY difficulty | Easy (DIY) — usually two screws and one connector; try MAF cleaner first |
| Recommended brands | Denso, Bosch, Hitachi, ACDelco |
Where to buy the part
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Frequently asked questions
Can I clean a MAF sensor instead of replacing it?
Yes — and you should try that first. Use a dedicated MAF cleaner (never brake cleaner or a cloth) to remove oil and dust from the sensing element. Cleaning fixes a large share of MAF-related codes for a few dollars.
What happens if I unplug the MAF sensor?
The engine switches to a backup estimate and often runs smoother if the MAF is badly dirty — a quick diagnostic clue that the MAF is your problem. Do not drive long-term unplugged.
Does a bad air filter damage the MAF?
A torn or oil-soaked filter (especially over-oiled aftermarket filters) is a leading cause of MAF contamination. Use a clean, properly fitted filter to protect the sensor.