P0102 Generic (SAE)

Mass or Volume Air Flow "A" Circuit Low Input

Updated 2026-10-02 · Fuel & air metering

Severity

Medium

Typical repair cost

20 – 350 EUR

System

Powertrain

What it means

The engine control unit monitors the mass air flow (MAF) sensor output and compares it against the air flow it expects for the current rpm and throttle position. P0102 sets when the MAF signal (voltage or frequency) stays below the minimum plausible value, for example under about 0.2–0.3 V or a reported flow of under 1–2 g/s while the engine is running. The ECU then falls back to a calculated air mass from throttle angle and rpm, which keeps the engine running but with degraded fuel control.

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Symptoms

Check engine light with a noticeable drop in power
Rough idle, stalling or hesitation on acceleration
Black smoke or rich fuel smell from the exhaust
Hard starting, especially when the engine is warm
Poor fuel economy and sometimes limp mode with limited rpm

Common causes

Contaminated MAF sensing element (oil from an over-oiled air filter, dust, silicone)
Open circuit, corroded connector or broken wire in the MAF signal or supply line
Missing 12 V supply or 5 V reference to the sensor, or a bad sensor ground
Failed MAF sensor hot-film element
Large air leak between the MAF and the throttle, so air bypasses the sensor
ECU driver fault (rare) or water intrusion in the sensor housing

How to diagnose

Inspect the intake tract from air box to throttle for cracked ducts, loose clamps or a collapsed hose; a leak after the MAF reads as low flow
With the engine idling warm, read MAF g/s on the scan tool: a rule of thumb is roughly 1 g/s per litre of displacement at idle (e.g. 2.0 L ≈ 2–3 g/s); on a snap throttle it should peak well above 100 g/s for a 2.0 L engine
Key on, engine off: verify 12 V (or 5 V on some makes) supply and a solid ground at the MAF connector, less than 0.1 V drop on the ground wire with the sensor powered
Backprobe the signal wire with the engine running; analogue sensors should read about 0.6–1.2 V at idle rising to over 4 V on wide-open throttle, frequency types roughly 2–3 kHz at idle
Clean the sensing element only with dedicated MAF cleaner, never touching the wire or film, then re-test; if values stay flat, substitute a known-good sensor
If the sensor and wiring test good but the reading is still low, check for a filthy air filter or restricted intake and verify the ECU connector pin for the MAF signal is not corroded

Frequently asked questions

Can I just clean the MAF sensor?

Cleaning with a dedicated MAF cleaner resolves a large share of P0102 cases caused by contamination. If the code returns within a few drive cycles after cleaning, the sensor element or wiring is at fault.

Why does the car run badly if the ECU has a fallback mode?

The fallback uses throttle angle and rpm tables that do not account for altitude, temperature or engine wear, so fuel trims drift and the engine runs rich or lean.

Does P0102 mean the sensor is dead?

Not necessarily. A broken wire, bad ground or a large intake leak after the sensor produce the same low reading, so test the circuit before buying a sensor.