Cause
Split or cracked intake hose
A split in the ducting between the airflow sensor and the throttle, admitting air the engine never measured. The position matters more than the size — a leak here is unmetered air, so the mixture goes lean and the module's corrections chase a quantity that was never counted.
The split is usually where the duct flexes, on the underside of a bend or at a concertina section, and it often opens only under engine movement or at certain loads. So the fault comes and goes and reads as a failing sensor, which is exactly what makes the airflow sensor the most over-replaced part on the engine.
Fuel trims tell you a leak exists; only a smoke test tells you where. Positive trims at idle falling away under load is the classic pattern, because the leak is a large fraction of a small airflow and a small fraction of a large one. Flex the ducting by hand with the engine running — an idle that changes as the duct is squeezed or twisted locates it without any equipment.
Typically an easy fix. Often worth checking before paying anyone to look.
Codes this can cause (5)
Codes where this is a likely explanation first, rather than merely a possible one.
- P012B Turbocharger/Supercharger Inlet Pressure Sensor A Circuit Range/Performance Likely for this code Moderate
- P2173 Throttle Actuator Control System — High Air Flow Detected Likely for this code High
- P2279 Intake Air System Leak Bank 1 Likely for this code Moderate
- P2281 Air Leak Between Mass Air Flow Sensor and Throttle Body Likely for this code Moderate
- P2280 Air Flow Restriction/Air Leak Between Air Filter and Mass Air Flow Sensor Bank 1 Moderate
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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