Are ECU codes & definitions different from one generation to the next? Specifically, from the 4th to 5th?

 

no, the change over was in 1996 (i think) for all cars. OBDII is a government set spec and was standarized in '96. if your car is '96 or later they are all the same. GM, Ford, and chrysler have different codes that other manufacturers. dont ask why.