Code P0100: air flow meter (MAF): circuit fault

Original definition (SAE J2012): Mass or Volume Air Flow Circuit Malfunction^[1][2]

• P0100Mass or volume air flow circuit malfunction (air flow meter circuit).
• P0103Air flow meter circuit (mass or volume air flow "A"): high input signal, that is, the MAF sensor signal exceeds the expected range.^{[8][9][10][11][12]}

1. 1Dirty, contaminated or faulty air flow meter: dust, oil or fuel residue covering the measuring element distorts the reading.^[1][2][3][6]
2. 2Sensor wiring and connector: loose or unplugged connector, corroded terminals, chafed or broken signal wire, interrupted earth wire, short circuit or blown fuse.^[1][2][3][6]
3. 3Air leaks in the intake, for example a cracked hose between the air flow meter and the throttle, a loose clip or an air filter box that is not closed properly.^[1][2][3]
4. 4Dirty or blocked air filter, or restricted airflow (clogged intake screen, intake with deposits or blocked catalytic converter).^[1][2]
5. 5Engine ECU fault: this is uncommon and only considered once everything above has been ruled out.^[1][2]

• Engine warning light on in the instrument cluster.^[3]Engine warning light: faults that cause it
• Loss of power.^[1][2][3]Less power: faults that cause it
• The engine may stall unexpectedly.^[1][2][3]Engine stalls: faults that cause it
• Rough idle, with the engine speed fluctuating.^[1][3]Vibrations: faults that cause it
• Jerking or hesitation when accelerating.^[1][2][3]Jerking: faults that cause it
• Starting problems.^[1]Hard to start: faults that cause it
• Noticeable increase in fuel consumption.^[1][3]Uses more fuel: faults that cause it
• Black smoke from the exhaust when accelerating.^[3]Black smoke: faults that cause it
• In some cars the ECU limits the engine speed (to about 2,500–3,000 rpm) as a safety measure.^[2]Limp mode: faults that cause it

1. 1Read all the stored codes and look at the freeze-frame data, a snapshot of the engine parameters at the moment of the fault: if there are other codes, it may be best to deal with them first.^[2]
2. 2Visually check the air flow meter connector (properly seated, with no loose terminals or corrosion), its wiring back to the ECU and the intake hoses between the filter, the air flow meter and the throttle: cracks, loose clips and an air filter box that is closed properly.^[1][2][3]
3. 3Check the air filter and replace it if it is dirty or blocked.^[1][2]
4. 4If the measuring element is dirty, clean it only with a cleaner made specifically for air flow meters (never with brake cleaner or solvents) and without knocking it. To test it, leave it fitted in its air filter box: removing it changes the airflow and its signal.^[1][3][13]
5. 5With a multimeter, check the reference voltage and the earth at the sensor connector.^[2]
6. 6With a diagnostic tool, read the air flow at idle and at about 2,500 rpm and compare it with the manufacturer's values; depending on the tool, the flow is given in g/s, kg/h or mg/s.^[3][13]
7. 7Only if, with the intake clean and airtight and the wiring correct, the reading is still out of range, replace the air flow meter; on some cars the learned mixture values then need to be reset. The ECU is checked last.^[1][2][3]