What does it mean?
At its core, the modern internal combustion engine is essentially the same as it has been for over a century. What’s really changed has been the addition of sensors and electronic controls, which has greatly improved power output, fuel economy, and emissions. At any given moment, down to the millisecond-level, the ECM is monitoring sensor readings, making calculations, and making minute adjustments to your engine’s function.
To achieve this level of control, ECM programming, as well as that of other system control modules, is so complicated and precise that automakers really don’t want anyone messing with it. Tampered or faulty programming could result in problems, such as poor fuel economy, poor combustion, or abnormal wear and mechanical failure.
All the information that the ECM needs, to manage your engine, is encoded in onboard memory, one type of which is referred to as EEPROM (electronically erasable programmable read only memory). Generally, EEPROM is programmed at the factory, programming depending on the vehicle, powertrain, transmission, trim level, and other vehicle-specific modules. Certain ECMs may also be programmable using factory scan tools. Some aftermarket mods may include such a feature.
If the ECM detects that its memory doesn’t match what is expected or has been compromised, it sets DTC P0602, “Engine Control Module (ECM) Programming Error,” and illuminates the malfunction indicator lamp (MIL).