Powertrain, generic · Fuel and air metering

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

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

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.

Likely causes

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

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

Repair estimate

DifficultyEasyDIY possible
Parts and labour€10–350
Time0.3–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

  1. Replace a dirty air filter
  2. Clean the MAF element with dedicated cleaner
  3. Check intake hoses for cracks
  4. Compare grams per second with the expected value at idle

Parts involved

mass air flow sensorintake ductair filterpcv system

Related codes

P0100P0102P0103P0106P0121P0171P010B

References: law.cornell.edu, gsi.ext.gm.com, gsi.ext.gm.com, saabwisonline.com.