The Electronic Control Unit (ECU) controls the fuel injection system, ignition timing, and the idle speed control system. The ECU also interrupts the operation of the air conditioning and EGR systems, and controls power to the fuel pump (through the control relay). The ECU consists of an 8-bit microprocessor, random access memory (RAM), read only memory (ROM), and an input/output interface. Based on information from the input sensors (engine coolant temperature, barometric pressure, air flow, etc.), the ECU determines optimum settings for the output actuators (injection, idle speed, ignition timing, etc.).