Circuit Description

The microprocessor contains a data storage area (keep alive memory) which can save pertinent data when ignition is turned off. Keep Alive Memory (KAM) data is lost if battery power or module ground is removed from module. KAM area is an integral part of microprocessor and cannot be serviced separately.

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 periodic checksum. The microprocessor also calculates a checksum on these memory locations when ever new data is written to them. This is called running checksum. To check KAM, the microprocessor compares periodic checksum to running checksum. If they do not match, the microprocessor sets DTC.