Cause
Ash loading at end of filter life
A particulate filter full of ash rather than soot, which is the end of its service life rather than a fault. The distinction is everything: soot is combustible and burns away in regeneration, while ash is incombustible and accumulates permanently.
Ash comes mostly from engine oil additives, so it builds in proportion to oil consumption and distance — which is why this arrives at a high mileage and why an engine that uses oil reaches it sooner. A filter that regenerates successfully and still reports a high restriction is ash-loaded, and no amount of forced regeneration will help.
The check is to compare soot load against measured restriction. A low calculated soot load with a high differential pressure means the restriction is not soot. Some filters can be professionally cleaned to remove ash; others are replaced. Excessive oil consumption shortens the next one's life the same way, so it is worth establishing whether the filter reached this at a normal mileage or early.
Typically specialist work. Needs equipment or training most home workshops do not have.
Codes this can cause (4)
Codes where this is a likely explanation first, rather than merely a possible one.
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