P0104: Mass Or Volume Air Flow Sensor "A" Circuit Intermittent
The air-flow sensor signal drops out or jumps for short moments.
Normal risk
Usually drivable, but the engine may hesitate or stall briefly. Have it checked soon.
Short answer · Can I keep driving with P0104?
Usually yes, carefully. The engine may stumble or stall for a moment. Have the connector and wiring checked soon.
What does P0104 mean?
Code P0104 means the mass air flow sensor signal is interrupted from time to time. Loose connectors, corroded pins and wiring that moves with the engine are the usual causes.
What the car does when the code is set
The check engine light comes on. Many engines switch to a substitute air value calculated from engine speed and throttle position. The car still drives, but it may hesitate, idle roughly, stall when coming to a stop or feel down on power, and fuel economy often gets worse.
How the system works
The mass air flow sensor sits in the intake between the air filter and the throttle. Most modern sensors use a heated film: air passing over it cools it, and the electronics convert the heating current into an air-mass signal, either as a voltage or a frequency. The engine control unit uses this value as the main input for fuel quantity, ignition timing and, on diesels, EGR control. It also checks the signal against a value it calculates from engine speed, throttle opening and other sensors, so it can detect when the reading is out of range or simply not plausible.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Dirty air-flow sensor elementOil or dust on the sensing element changes its reading.
- Air leak after the sensorA split intake duct lets in air the sensor does not measure.
- Wiring or connector faultCorroded pins or a damaged wire change the signal.
- Blocked air filterA very dirty filter reduces the air flow.
- Faulty sensorThe sensor itself fails.
How it is diagnosed
- Check the connector and wiringLook for corrosion, loose pins and damaged wires between the sensor and the engine control unit.
- Inspect the intake pathCheck the air filter and the duct between the sensor and the throttle for splits and loose clamps.
- Compare live dataCompare the air-flow reading at idle and when revving with the specification for your engine, and with the calculated load.
- Test supply and signalWith a multimeter or oscilloscope, check the supply voltage, ground and signal as described in the service data.
Questions about P0104
How do I find an intermittent fault?
A workshop watches the live signal while gently moving the connector and wiring. A jump in the reading shows where the fault is.
Can I drive without the air-flow sensor connected?
Many engines run on a backup map without it, but power and fuel economy suffer and other codes appear. It is not a fix.
Can an oiled air filter affect the sensor?
Yes. Too much oil on reusable cotton filters can coat the sensor element and change its readings.