Cause
Poor permanent supply connection
High resistance in a module's permanent live feed. The distinction from a blown fuse is that everything appears to work — the module powers up, communicates and answers questions, and only loses its memory when the vehicle sleeps and the current available through a resistive joint is not enough to hold it.
So the symptoms are intermittent and look like software: adaptations occasionally lost, a clock that sometimes resets, keep-alive memory codes appearing at random. Measure voltage drop on the permanent feed with the vehicle asleep rather than resistance at rest, which a marginal joint passes easily. Corroded joints behind trim or at a body earth are the usual place, and a supplementary lead fitted temporarily is a quick confirmation.
Typically a moderate job.
Codes this can cause (1)
Codes where this is a likely explanation first, rather than merely a possible one.
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