Cause
Severely blocked air filter
An air filter so restricted that it limits airflow into the engine. A moderately dirty filter costs almost nothing measurable, which is why this entry says severely: the fault is a filter that has been left far beyond its interval, soaked with oil or water, or blocked by debris drawn in.
The engine is starved in proportion to demand, so idle and light throttle are normal and full load is not. The complaint is a power loss under acceleration with black smoke on a diesel, and the module reports airflow below expectation or a mixture it cannot correct.
Check it by looking rather than by mileage. Hold it to a light — a filter that passes none is finished, whatever the service record says. A filter soaked with oil points upstream at a crankcase breather flooding the intake, and one blocked with nesting material or leaves points at where the vehicle is parked; in both cases replacing the filter alone leaves the cause in place.
Typically an easy fix. Often worth checking before paying anyone to look.
Codes this can cause (2)
Codes where this is a likely explanation first, rather than merely a possible one.
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