P0102 Mass Air Flow Circuit Low Input
The airflow sensor's signal is too low — either it's failed, it's filthy, or its wiring is broken.
Fuel & air
Where P0101 means an implausible reading, P0102 means the signal voltage or frequency is below the valid range entirely. The ECU falls back to a default fuelling table calculated from throttle position and RPM, which is why the car usually still runs but feels flat and drinks fuel.
Diagnose P0102 on your specific vehicle Add your year, make and model for ranked causes, repair videos and the exact parts you needCan I keep driving?
Driveable
Usually yes, with reduced power. Not a stranding fault in most cases.
How serious
Moderate. Limp-mode fuelling is safe but crude.
Symptoms you'll notice
- Loss of power and sluggish throttle response
- Rough idle or stalling
- Hard starting
- Poor fuel economy
- Black smoke in some cases
What causes P0102
Ordered by what to check first — how likely each cause is, weighed against what it costs to rule out. Working down the list in order is what stops you replacing an expensive part to fix a cheap problem.
Heavily contaminated or failed MAF sensor
A thick oil or dust film can drop the signal out of range altogether. Clean it first; replace it if cleaning doesn't restore the signal.
Broken or shorted wiring
An open signal wire, a chafed harness, or a corroded connector produces exactly this. Inspect and back-probe before replacing the sensor.
Loss of supply voltage or ground
The sensor needs a good reference and ground; a failed ground point makes a healthy sensor read as dead.
Severely restricted air intake
A collapsed intake duct or a filter packed solid with debris can genuinely reduce airflow below the sensor's valid range.
How to diagnose it
- Inspect and unplug the MAF connector, looking for bent pins, corrosion and oil intrusion.
- With the key on, check for supply voltage and a good ground at the connector.
- Clean the sensor element with MAF cleaner and re-test.
- Watch MAF readings on live data while revving — a signal stuck at or near zero confirms the circuit rather than a calibration problem.
- Inspect the air filter and intake ducting for collapse or blockage.
Parts you might need
Tools for the job
- Multimeter
- MAF sensor cleaner
- OBD-II scanner with live data
Related trouble codes
- P0101 — Mass Air Flow Circuit Range/Performance Problem
- P0171 — System Too Lean (Bank 1)
- P0113 — Intake Air Temperature Sensor 1 Circuit High Input
Fitment matters. Causes and parts above are the common cases for P0102 across vehicles. The specific part numbers, procedures and torque specs vary by year, make, model and engine — always confirm against service data for your vehicle before buying parts or starting work.