Circuit Description

The control module contains a block of memory locations in which the data remains the same at all times. This memory is referred to as Read Only Memory (ROM). When ignition is turned on, the control module will add all of the data in these ROM locations and will compare the total to a calibrated, or checksum, number. If these 2 numbers do not match, DTC will be set. DTC will set when the data checksum does not match the expected value.