Fault codeP0101

MODERATE

Mass or Volume Air flow Circuit Range/Performance Problem

What this code means

Mass or Volume Air flow Circuit Range/Performance Problem.

P0101 is a generic code: it means the same thing on every make. P0101 belongs to family P01xx — Fuel and air metering. Its page explains how to read a code and groups all its codes by part.

Mass airflow sensor (airflow meter)

The airflow sensor sits in the intake duct between the air filter and the throttle. A heated wire or film measures how much air enters the engine, and the control unit uses it to calculate how much fuel to inject.

Symptoms

Lack of power, hesitation under acceleration, rough idle, occasional stalling, higher consumption and sometimes black smoke. The airflow sensor sends a value the control unit finds inconsistent with revs and load: too much air or too little compared with what it expects.

Common causes

Airflow sensor fouled with oil or dust — especially with an oiled “performance” air filter
Air leak between the sensor and the throttle, letting unmeasured air in
Clogged or badly fitted air filter
Faulty sensor (worn heating element)
Leaking EGR valve or crankcase ventilation, skewing the reading

How to diagnose it

In live data, mass airflow at warm idle should be roughly proportional to engine size — around 2 to 4 g/s per litre. A value clearly too low points to fouling or an air leak; too high to a sensor at the end of its life.

Clean the sensor with a specific airflow sensor cleaner, never brake cleaner, which damages the hot wire. Check the whole length of the intake duct: a split under a clamp is easily missed.

Watch it live in Klaro

With an OBD2 adapter plugged in, these live readings show the part at work, when your car reports them:

Mass air flow
Intake manifold pressure
Short term fuel trim bank 1
Long term fuel trim bank 1

What to do

Have it checked this week. The car remains usable, but the fault will not clear itself and will fail the roadworthiness test.

Clearing a code switches the light off but repairs nothing: if the fault remains, the code comes back. Clearing a fault code yourself →

Repair cost

Airflow sensor cleaner: around €10. New sensor: €60 to €250 depending on brand — avoid €20 copies, they create other faults. Intake hose: €20 to €80.

How to read this code

PPowertrain
0standardised code
1Fuel and air metering
01P0101