Circuit Description

This fault is internal. No external circuits are involved. Module microprocessor must be active/awake for DTC to set. Microprocessor calculates check sum on those areas of memory that hold critical operation data. This is done at a regular interval and is called periodic check sum. Microprocessor also calculates a check sum on these memory locations when ever new data is written to them. This is called running check sum. Microprocessor compares periodic check sum to running check sum. If they do not match, the microprocessor sets DTC B1004.

When DTC is set, microprocessor reverts back to base programmed critical operating data until new data is learned and stored in KAM. DTC will clear when microprocessor calculates successful comparison of periodic check sum to running check sum.