P0104
Mass or Volume Air Flow Sensor A Circuit Intermittent.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 1
- AreaFuel and air metering
- 04
- FaultThe specific fault in that area
What it means
P0104 is the generic code for an intermittent fault in the mass or volume air flow sensor 'A' circuit. The engine control unit has seen the air flow signal drop out, spike or jump to an implausible value for short periods, rather than staying faulty all the time. It usually points to a wiring, connector or sensor problem that comes and goes.
Symptoms
- Malfunction indicator lamp on, possibly flashing on and off with the fault
- Intermittent hesitation or stumbling under acceleration
- Rough or unstable idle that comes and goes
- Occasional stalling or difficulty restarting
- Poor fuel economy or occasional black smoke
- Engine surging or momentary loss of power
Possible causes
- Loose, corroded or damaged connector at the air flow sensorlikely
- Chafed, broken or high-resistance wiring between the sensor and control unit, including power or earth supplylikely
- Faulty or contaminated air flow sensor element giving intermittent readingslikely
- Unmetered air entering after the sensor from a split intake hose, loose clamp or leaking jointpossible
- Damaged, wet or poorly fitted air filter housing or intake ducting disturbing the airflow past the sensorpossible
- Low or unstable system voltage from a weak battery, poor earth or charging faultpossible
- Fault within the engine control unitrare
How to diagnose
- Read all stored and pending codes and note the freeze frame data (engine load, rpm, temperature) to see when the fault occurred
- Check for other codes such as fuel trim, misfire or throttle faults that could point to an intake leak or a shared supply fault
- Inspect the air flow sensor connector for corrosion, bent or pushed-back pins, and a secure fit; check the wiring for chafing and damage
- Inspect the intake tract from the air filter housing to the throttle body for splits, loose clamps, and a correctly fitted air filter
- With the engine running, watch live air flow data and gently wiggle the connector and harness to see if the reading drops out or spikes
- Compare the live air flow reading at idle and with the engine speed held steady against the manufacturer's expected values for that engine; the specification varies by model
- Check the sensor supply voltage, signal and earth with a multimeter against the wiring diagram for that vehicle, and check battery and charging voltage
- Check the sensor element for contamination or damage only as the manufacturer permits, as the correct method depends on the sensor type
How to fix
- Clean, repair or replace the sensor connector and terminals if corroded or loose
- Repair or replace damaged wiring, including power and earth faults found during testing
- Replace the air flow sensor if it gives erratic readings that cannot be traced to wiring or air leaks
- Repair intake leaks by replacing split hoses and refitting or replacing clamps and seals
- Refit or replace the air filter and housing correctly if airflow around the sensor is disturbed
- Repair the battery, earth or charging fault if system voltage is unstable
Can I keep driving?
Medium severity
The car can usually be driven for a short time, but intermittent stalling or hesitation can be unsafe in traffic, so get it checked soon. Avoid heavy loads and long journeys until it is diagnosed.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.