P0101 P0xxx · Powertrain (P) Medium severity
Mass Air Flow Circuit Range / Performance
The MAF reading does not match what the ECU expects for the given RPM, throttle and load. Either the sensor is dirty/out of range, or air is entering the engine without being measured.
Severity guidance: Medium — drivability or emissions affected, book it in this week
Symptoms you will notice
- Hesitation on acceleration
- Lean or rich fuel trims
- Poor idle
- Black smoke on some diesels
Common causes
Ordered from most to least likely — start at the top.
- 1 Contaminated MAF hot-wire or hot-film element
- 2 Air leak after the MAF (split intake boot, loose clamp, cracked PCV hose)
- 3 Clogged air filter
- 4 Wrong or non-original sensor
How to diagnose it
Cheapest and least invasive first — most of these codes are not a parts problem.
- ✓ Read MAF grams/second at warm idle and compare with the specification (roughly 1 g/s per litre of displacement).
- ✓ Inspect the whole intake tract from the airbox to the throttle body for loose clamps and cracks.
- ✓ Clean the element with dedicated MAF cleaner only — nothing else.
- ✓ Smoke-test the intake if the leak is not visible; a smoke machine finds it in minutes.
Repair options
- Clean or replace the MAF sensor
- Repair the intake leak
- Replace the air filter
P0101 — frequently asked questions
Can I clean the MAF with brake cleaner? +
No. Use only MAF-specific cleaner; other solvents damage the sensing element.
Why is the fuel trim positive at idle but normal at speed? +
Classic vacuum leak signature — unmetered air matters most when airflow is small.
Confirm the diagnosis before you buy parts
Send us the code, freeze-frame data and the vehicle — our engineers will tell you what to test first.