Summary
P0100 means the PCM has detected a general malfunction in the mass air flow sensor circuit. The MAF sensor measures how much air enters the engine so the PCM can calculate the correct fuel delivery. The most common cause is a failed MAF sensor (40%), followed by a dirty sensing element (25%) and wiring or connector problems (20%). Start with a $8 MAF cleaning before replacing parts — it resolves roughly a quarter of P0100 cases.
Severity: Moderate
Safe to drive: Yes, short distances — engine runs on estimated airflow values
Repair cost: $8–$300 depending on cause
DIY difficulty: Easy to Moderate
What does P0100 mean?
The mass air flow sensor sits between the air filter box and the throttle body. It measures the volume and density of air entering the engine, sending a voltage or frequency signal to the PCM. The PCM uses this reading to calculate how much fuel to inject — get the air measurement wrong, and the entire fuel mixture is off.
P0100 is the general circuit code for the MAF. Unlike P0102 (low input) or P0103 (high input), which point to a specific signal direction, P0100 indicates the PCM sees something broadly wrong — the signal may be missing, erratic, stuck, or outside the sensor's valid operating range. The PCM can't trust the reading and falls back to estimated airflow based on throttle position and RPM, which hurts performance and fuel economy.
On most vehicles, the PCM sets P0100 when the MAF signal voltage or frequency is outside its expected range, or when the signal doesn't respond to changes in engine load and throttle position.