P0100 Generic (SAE)

Mass or Volume Air Flow "A" Circuit

Updated 2026-10-02 · Fuel & air metering

Severity

Medium

Typical repair cost

30 – 450 EUR

System

Powertrain

What it means

The ECU monitors the mass air flow (MAF) sensor signal for electrical plausibility. P0100 sets when the signal voltage or frequency is outside the whole working range (for example stuck at 0 V or at reference voltage) or when the signal is lost entirely, indicating a circuit fault rather than merely a low or high reading. The ECU then substitutes a calculated air mass from throttle position and rpm.

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Symptoms

Check engine light with the engine running in substitute-value mode
Hesitation, surging or stumbling on acceleration
Black smoke or rich smell from a poorly calculated fuel map
Rough idle, stalling after start or when coming to a stop
Noticeable fuel consumption increase and sluggish response

Common causes

MAF sensor failed internally (hot-film element burnt or contaminated)
Broken, chafed or corroded wiring between MAF and ECU, especially the 5 V reference or signal wire
Connector pins spread or green from moisture ingress
Missing 12 V supply (blown fuse or relay) to the sensor
Oil from an over-oiled aftermarket air filter coating the sensing element
ECU input fault (rare)

How to diagnose

With the key on, check the MAF connector: expect battery voltage (12-14 V) on the supply pin, 5 V on the reference pin (if used) and under 0.1 V drop on the ground pin
Key on, engine off, measure the signal wire: analogue sensors should read 0.2-1.0 V (not 0 V or 5 V); frequency types should output a stable 1.5-3 kHz baseline
Start the engine and watch MAF live data: a typical 2.0 L engine shows 2-5 g/s at idle and 100-200 g/s at wide-open throttle under load; a flat reading of 0 g/s or a fixed maximum confirms a circuit fault
Snap the throttle and confirm the signal voltage rises smoothly to 3-4.5 V; a frozen or jumping value with good wiring means a dead sensor
Perform a wiggle test on the harness and check continuity (under 1 ohm) and insulation to ground on each wire back to the ECU
Inspect the sensing element for oil, dust or insect debris; clean only with dedicated MAF cleaner, never touch the wires

Frequently asked questions

Can I drive with P0100?

Yes, the ECU uses a fallback map, but fuelling is coarse and the catalyst can suffer from rich running over time.

Should I clean or replace the MAF?

Try cleaning first if the element is dirty; if the signal is absent or fixed with good supply and ground, the sensor is dead and must be replaced, preferably with an OEM-quality part.