Mémoire du calculateur dégradée

The non-volatile memory holding a module's learned values and configuration has lost or corrupted part of its contents.

It is a real failure mode and a rare one, and its position on any diagnostic list should be last. Nearly everything that looks like lost module memory is something cheaper: a module reprogrammed or replaced, a programming session that did not complete, a supply or ground problem browning the module out, or a calibration step simply never carried out. All four are commoner, and all four are recoverable without a new module.

What makes genuine memory degradation identifiable is that it recurs without explanation. Values are entered correctly, verified by reading them back, and are gone or altered later with nothing having been done to the vehicle in between. A single instance of missing data is not evidence of this; a documented second loss after a verified correct entry is.

The usual culprits behind it are age and heat — memory cells lose retention over many years, and a module mounted somewhere hot ages faster — along with sustained low voltage, which is why chronic charging or earth faults belong in the investigation before the module does.

The practical order is therefore: fix the supply and grounds, reprogram and re-enter the adaptations, verify by reading back, and only if the values are lost again treat the module itself as the fault.