In order to reverse-engineer an ECM, what has been done on other makes has been to read the contents of the memory (in some cases it's on a removeable chip) and use a de-assembler to determine what the code started out as. You will need to know what processor is in the ECM - hopefully it's a standard microprocessor and not some custom OEM-specific version. The de-assembler turns the machine-level instructions into readable code (if you understand machine language). And of course you will have to separate data from instructions, a symbol table really helps there. An ECM bench also makes the process a little more manageable.