Circuit Description

EEPROM check sum error detection is internal. No external circuits are involved. For DTC to set, microprocessor must run program to detect a check sum error after each "power up". The only requirements are voltage and ground. Program runs even if voltage is out of operating range.

Microprocessor retains an inverse copy of digital value stored in certain blocks of memory in EEPROM. Microprocessor then reads information from those blocks and adds stored inverse value to current value. If they do not equal 0, microprocessor sets DTC B1009.

When DTC is set, microprocessor reverts to base operation values programed for those blocks of data that have failed check sum test. Blocks of data that have not failed check sum test are not affected. DTC clears when microprocessor runs successful check sum test of EEPROM.