رحلات قصيرة متكررة تقطع عملية التجدد

A usage pattern rather than a fault, and the commonest reason a diesel particulate filter fills up. A regeneration needs fifteen to thirty minutes of sustained running to complete, and a journey that ends before then aborts it — so a car used for short local trips can attempt regeneration repeatedly and never finish one.

The damage is cumulative and invisible. Fuel injected for a regeneration that is then abandoned drains past the piston rings into the sump, so the oil level rises and the oil is progressively diluted with diesel. An oil level above maximum on a diesel is a genuine hazard rather than a curiosity, because the engine can begin to run on its own oil.

The remedy is a change in use, not a part: an occasional sustained run at steady speed, in a gear that keeps the engine turning reasonably fast, and not switching off while a regeneration is running. Fitting a new filter to a car that keeps the same pattern simply restarts the clock.