Conditions for Setting the DTC
WARNING: This page is about a different car, the 2004 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
The microprocessor calculates a checksum on those areas of memory that hold critical operation data. This is done at a regular interval and is called the periodic checksum. The microprocessor also calculates a checksum on these memory locations when ever new data is written to them. This is called the running checksum.
To check the keep alive memory (KAM), the microprocessor compares the periodic checksum to the running checksum. If they do not match, the microprocessor sets the DTC.