Cause
Pressure sensor hoses fitted the wrong way round
The two hoses of a differential pressure sensor swapped. The sensor measures the difference between two points, so reversing them inverts the sign of everything it reports.
The module reads a negative restriction as an implausible value or, worse, as a filter that is unusually clear — so it either reports a rationality fault or never regenerates while the filter loads. Every component is perfect and correctly connected, just to the wrong port. It is a repair-induced fault, so the timing identifies it: a filter or sensor fault beginning immediately after work on the exhaust. Check the routing against the diagram rather than against how it looks, since the hoses are the same size and reach both ports comfortably.
Typically an easy fix. Often worth checking before paying anyone to look.
Codes this can cause (1)
Codes where this is a likely explanation first, rather than merely a possible one.
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