The MEG is fitted to all petrol cars with the EDG fitted to the diesels. Collectively, these are known as the ECU. The ECU is a solid state microprocessor board with the following key components inside:

The device functions are as follows:

• SAM/ZEE connections link the ECU to the central electronics.
• Engine connections link all the sensors to actuators within the engine.
• The processor does exactly what it says - it processes all the inputs and gives different outputs.
• The EEPROM contains the program to run the engine. It is this chip to which remaps are written to.
• The capacitor supresses any voltage spikes from the alternator or battery to prevent damage to the ECU.