OBD CodesWhat it means
The mass air flow sensor sits in the intake pipe, just after the air filter, and measures how much air the engine is drawing in. The computer uses that figure to decide how much fuel to inject. These codes mean the reading is missing, or does not match what the computer expects for the engine speed and throttle position.
Codes in this group
| Code | Meaning |
|---|---|
| P0100 | Mass air flow sensor circuit fault |
| P0101 | Mass air flow reading out of the expected range |
| P0102 | Mass air flow signal too low |
| P0103 | Mass air flow signal too high |
| P0104 | Mass air flow signal cuts in and out |
Bank 1 is the side of the engine that has cylinder 1. Sensor 1 is before the catalytic converter and sensor 2 is after it. More terms explained.
What you may notice
- Rough or hunting idle
- Hesitation or flat spots when you accelerate
- Higher fuel use
- Hard starting or stalling just after start
Common causes
Most likely first:
- A dirty or contaminated sensor, often from an over-oiled or poor air filter
- An air leak in the intake pipe between the sensor and the engine
- A clogged air filter
- A loose connector or damaged wiring
- A failed sensor
What to check first
- Look at the air filter and replace it if it is dirty
- Check that the intake pipe and its clips are tight and not cracked
- Check the sensor plug is fully seated
- A workshop can clean the sensor with the correct cleaner and read its live values
Have a mechanic confirm. A fault code tells you which system reported a problem, not which part has failed. The same code can have several causes, and they differ between car models. Use this page to understand the code, then have a qualified mechanic test the car before any part is replaced.
After the repair
Once the cause is fixed, the code can be cleared with a scan tool, or the warning light goes out by itself after several trips without the fault. Clearing a code without fixing the cause only hides it for a while. More about clearing codes.
Related codes
Manifold pressure (MAP) and barometric sensor (P0105), Intake air temperature sensor (P0110), Engine coolant temperature sensor (P0115), Thermostat and engine warm-up (P0125), Throttle position sensor (P0120), Accelerator pedal sensor and throttle agreement (P2120), Electronic throttle actuator (P2100), Oxygen sensor before the catalytic converter (sensor 1) (P0130). All codes.
Written in November 2026. These are generic OBD-II codes, the same on all makes. Causes and repair steps differ between models.