The mass airflow (MAF) sensor measures the air entering the engine so the computer can add the right amount of fuel. When it is dirty or failing, the engine can hesitate, idle roughly, stall after starting, run lean or rich and set codes such as P0101, P0171 or P0174. Cleaning the sensor with a dedicated MAF cleaner often fixes a contaminated sensor.
How a MAF sensor works
Most MAF sensors use a heated wire or film in the intake air stream; the electrical power needed to keep it at temperature as air flows past tells the computer how much air is entering. It sits in the intake duct between the air filter and the throttle body.
MAF sensor symptoms
- Hesitation, surging or poor acceleration
- Rough idle or stalling shortly after starting
- Poor fuel economy
- Black smoke if it over-reports airflow; see exhaust smoke colors
- Codes for MAF range or performance, or lean codes on both banks
How to clean a MAF sensor
- Unplug the sensor and remove it from the intake duct, usually two small screws.
- Spray the sensing element with MAF sensor cleaner only; other cleaners can leave residue or damage it.
- Do not touch the wires or film.
- Let it dry completely before refitting and reconnecting it.
What contaminates a MAF
- Over-oiled reusable air filters
- A torn or poorly sealed air filter letting dirt through
- Oil vapor from the crankcase ventilation system; see PCV valve
Before you replace it
Check the air filter, the intake duct for cracks after the sensor, and the connector, and try cleaning the sensor first. A new sensor will not fix a vacuum leak or a torn duct that lets unmeasured air in.
MAF vs MAP sensors
Some engines measure airflow directly with a MAF sensor, while others estimate it from manifold pressure (MAP), engine speed and temperature, known as speed density. Many engines use both. Boosted builds often move to speed density or a recalibrated MAF because the factory setup was not designed for the extra airflow. If a MAF fails, many engines fall back to estimated airflow and run poorly until it is fixed.
Intakes and MAF calibration
Changing the intake tube diameter or the sensor housing changes how the MAF reads, which is why some intakes need the engine computer adjusted; see what does a cold air intake do? Supercharger kits route the MAF into their own ducting; the ECS NOVI kits we carry list ducting with MAF locations. See supercharger kits.
Related: vacuum leak · throttle body.
More guides: MAP sensor · O2 sensor · fuel trim · car hesitates when accelerating · car loses power when accelerating.
Trouble codes: P0101 MAF Sensor Range/Performance · P0102 MAF Sensor Circuit Low · P0103 MAF Sensor Circuit High · P0113 Intake Air Temp Sensor High · P0171 System Too Lean Bank 1 · P0068 MAP/MAF Throttle Position Correlation · P0110 IAT Sensor Circuit · P0112 IAT Sensor Circuit Low · P0111 IAT Sensor Range/Performance · P0114 IAT Sensor Intermittent · P0100 MAF Circuit Malfunction · all OBD2 codes.
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