Q: What Are Reprogrammable Car ECUs?

An electronic control unit (ECU) is comprised of many different computer parts soldered onto a circuit board to make up a complete ECU. The ECU uses different kinds of memory on its computer board. These memory chips are used for different reasons and work in different ways. Some computer chips are designed to be reprogrammable and others are not. Some memory chips will keep their memory as long as power is supplied to them and others will keep their memory even if power is removed or lost.

The memory in a car’s computer ECU that holds the programming to control the running of your engine is called EEPROM or electrically erasable programmable read only memory. This memory can be programmed and reprogrammed electrically to be able to upgrade or change the programming that controls the engine functions. The chip is most commonly used for a vehicle’s calibration file to operate the engine within specifications of the manufacturer. It is a non volatile chip meaning it will keep its memory even if power is lost. The chip can be reprogrammed to change the calibration if changes are needed.

Another computer chip called ROM, or read only memory, can only be programmed once. It cannot be reprogrammed once it is programmed. This memory is used to perform basic computer operating functions only and will not be changed even if power is removed the same as the EEPROM. The ROM will store basic memory functions to operate the onboard diagnostics and other basic functions that do not need reprogramming. https://www.yourmechanic.com/services/service-light-is-on-inspection

The reprogrammability of the ECU memory has been around for over 15 years in vehicles and is used extensively in different modules and ECUs throughout the vehicle. This memory is used in transmission, ABS, body, engine, suspension, AC, ride control and other ECU modules of today’s vehicles. This memory is very reliable and rarely fails. If the program put on it is bad or needs updating, then it can be electronically erased and the new program installed. Once it is installed, the new program can be used as needed. If the chip itself has internal failures, the ROM can detect this since it checks the EPROM every time you turn on your key. If errors are found, then a code is set into the computer storage memory chip or another EEPROM.