Summary
P0101 means the MAF sensor's readings fall outside the expected range for the current engine RPM and throttle position. The sensor is communicating, but its numbers don't make sense to the PCM. The most common cause is a dirty MAF element (35%), followed by an intake air leak after the sensor (25%) and a restricted air filter (15%). A $8 MAF cleaning and a quick intake inspection resolve the majority of P0101 cases.
Severity: Moderate
Safe to drive: Yes, short distances — fuel mixture may be off
Repair cost: $8–$300 depending on cause
DIY difficulty: Easy to Moderate
What does P0101 mean?
The PCM knows roughly what airflow to expect at any given RPM and throttle opening. It builds this expectation from factory calibration data. When the MAF sensor reports a value that doesn't match — either too high or too low for current conditions — the PCM flags P0101.
This is different from P0100 (general circuit fault), P0102 (low signal), or P0103 (high signal). P0101 means the sensor is electrically functional and within its voltage range, but the actual airflow reading is implausible. Think of it as a "rationality check" failure — the MAF says one thing, but the engine's behavior says another.
Common scenarios: the MAF reads low because its element is dirty, but not so low that it triggers P0102. Or the MAF reads correctly, but an air leak after the sensor adds unmetered air that the PCM detects through fuel trim corrections.