Technician Handbook ! 673 Electronic & Computer Controlled Systems ECU Memory Like other computers, ECUs have internal memory. Besides storing DTCs, they can also store switch settings and component positions. Over time, ECUs can acquire and store information about the vehicle’s operating characteristics and driver/occupant preferences. The data stored in memory can have a direct affect on how well the vehicle operates and the driver’s perceptions of comfort and convenience. Types of ECU Memory Volatile memory chips are the type that require constant power to maintain what is stored in them. When the power is removed, their memory contents are erased.
These types of memory chips are used for ordinary microprocessor memory. (RAM for example.) Non-volatile memory chips retain their contents even when the power is removed. These types of memory chips permanently store the microprocessor’s operating instructions, or logic. (ROM for example.) Programmable Read Only Memory (PROM) – A memory chip that can be programmed once, but cannot be reprogrammed. Erasable Programmable Read Only Memory (EPROM) – A programmable chip that can be removed from its circuit and reprogrammed. Electrically Erasable Programmable Read Only Memory (EEPROM) – A programmable chip that can be electrically erased and reprogrammed without removing it from the circuit.
Technical Training 19