P0101: Mass or Volume Air Flow Sensor A Circuit Range/Performance

What does P0101 mean?

The mass air flow sensor (MAF) sits between the air filter and the throttle or compressor and measures how much air the engine draws in; fuel quantity, load and ignition are calculated from it. Most are hot-film or hot-wire sensors that output either a voltage or, on GM, Saab and newer Ford systems, a frequency. P0101 is a plausibility fault: the signal is electrically fine but does not match the engine's state. GM petrol engines model the expected air flow from manifold pressure, throttle, speed and boost and blame the MAF if it is off by more than 20 g/s; GM diesels check the measured-to-estimated ratio (0.8–1.2) with EGR closed; Bosch ME9 compares it with the throttle angle. Common causes are air leaks after the sensor, a soiled element (oiled sport filters) or a disconnected crankcase vent; GM also documents a bad crimp in the fuse box. Ford uses P0068 instead. Two trips are needed.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Check engine light on, often without driveability problems
• Hesitation, flat spot, poor throttle response
• Rough idle or stalling
• Higher consumption, often with lean codes P0171/P0174

Common causes

• High Air leak between sensor and engine (cracked or loose intake duct, boost leak)
• High Contaminated sensing element (oil from oiled sport filter, dust)
• Medium Leaking or disconnected crankcase ventilation
• Medium Clogged or wrongly fitted air filter, modified intake
• Medium Aged sensor or poor contact in the wiring

Likelihood is a general estimate across vehicles; your make and model may differ.