P064F: invalid authentication table in ECU software

P064F indicates that the ECU software contains an invalid Message Authentication Code Table, abbreviated MACT, in this GM monitor. The generic unauthorized-software title is implemented here as a specific software-authentication result.

What the result establishes

The criterion is an invalid embedded MACT. The summary does not say who changed the software, whether a modification was intentional or whether the condition arose during a service event. It would be unsupported to treat the code as proof of owner tampering.

Unlike a sensor-range monitor, this row supplies no voltage threshold, engine-speed window or sample-count filter. It requires the calibration enable flag and lists Type A, one-trip reporting, with the timing field marked not applicable.

Useful service questions

Establish the installed ECU software and calibration identity and whether there is a relevant programming history. These are diagnostic follow-ups derived from the authentication target, not a claim that the source specifies a particular reflash operation.

Verification should confirm that the applicable authentication check accepts the software state after any authorized service correction. Clearing memory alone cannot demonstrate that the embedded table has become valid. The page provides no update file, controller-replacement rule or method for bypassing authentication. Exact vehicle and controller service information is needed before changing software, and a code alone does not prove that the entire ECU hardware is defective.

Source and applicability

2025 GM 25OBDG04B diagnostic parameter tables; the cited monitor only. Vehicle, engine and calibration applicability must be confirmed separately. These tables describe detection logic, not a complete repair procedure or a component replacement verdict. gm-2025-04b, PDF page 629.