حشوة مرشح الجسيمات متشققة أو تالفة

The filter's ceramic substrate cracked or partly melted, so exhaust passes without being filtered. A cracked filter stops filtering while its restriction falls, which produces a diagnostic paradox: the differential pressure reads lower than a healthy filter's, and a module reading only pressure could conclude the filter is unusually clear.

That is why the downstream particulate sensor matters, and why the two readings together are the diagnosis: low restriction with soot detected downstream means the substrate has failed, not that the filter is clean. Visible soot at the tailpipe on a diesel is the confirming evidence and should not happen on a working filter.

Substrates crack from thermal shock or from an uncontrolled regeneration. A filter that was heavily loaded when it finally regenerated can reach temperatures that melt it — so this failure is frequently the end of a sequence of aborted regenerations. Establish why before fitting a replacement, or the new one meets the same conditions.