What Is P0102?
P0102 means the MAF sensor signal voltage is below the minimum threshold the ECU expects - the signal is stuck at an abnormally low level rather than varying with airflow. Unlike P0101 where the sensor produces a plausible but inaccurate reading, P0102 indicates the output voltage has dropped below the valid electrical range, typically below 0.5V on most sensor types.
A low MAF input causes the ECU to calculate much less airflow than is actually entering the engine. In response, the ECU under-fuels relative to actual airflow, but the fallback fuel strategy on most ECUs adds enrichment to compensate, often resulting in rich running in limp-home mode. The code points primarily to a wiring, earth, or sensor power supply fault.
Common Symptoms
- Engine management light on
- Sluggish or flat performance
- Poor throttle response
- Possible rich running in limp-home mode
- Rough idle
- High fuel consumption
Common Causes
How to Diagnose P0102
Check MAF Connector and Wiring
Disconnect the MAF and inspect the connector for corrosion, bent pins, and damaged wiring. Check the signal wire and earth wire from the MAF back to the ECU for breaks or heat damage.
Measure Supply Voltage
With ignition on, check supply voltage at the MAF connector power pin. Should be 5V (MAP-style) or 12V depending on sensor type. No voltage indicates a fuse or wiring break.
Measure Earth Integrity
Check continuity between the earth pin on the MAF connector and the ECU earth point. High resistance (above 1 ohm) confirms an earth circuit fault.
Monitor MAF Live Data
Read MAF value at idle. A healthy sensor shows 2–10 g/s at idle. A reading stuck at 0 or below 0.5 g/s when the engine is running confirms a circuit-level low input rather than a performance issue.
Replace MAF Sensor
If voltage supply and earth are correct but the signal is stuck low, the sensor has failed internally. Replace with a quality aftermarket or OEM sensor.
Verdict
Check supply voltage and earth continuity at the MAF connector before replacing the sensor. A broken earth wire is a cheap fix that is easily missed. If both supply and earth are correct and the signal is stuck low, sensor replacement is confirmed.
Want the full picture? The OBD Fault Code Plain English Guide (PDF) covers the most common UK fault codes in one plain-English download.
