Cause
Degraded module memory
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.
Typically specialist work. Needs equipment or training most home workshops do not have.
Codes this can cause (7)
Codes where this is a likely explanation first, rather than merely a possible one.
- P062F Internal Control Module EEPROM Error Likely for this code High
- P0601 Internal Control Module Memory Checksum Error High
- P0603 Internal Control Module Keep Alive Memory (Keep Alive Memory) Error Moderate
- P0604 Internal Control Module Random Access Memory (RAM) Error High
- P2673 Injection Pump Timing Calibration Not Learned Moderate
- P2674 Injection Pump Fuel Calibration Not Learned Moderate
- P2690 Cylinder 5 Injector Data Incompatible Moderate
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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