This paper is about simulation design of an Electronic Control Unit (ECU) for an adaptive cruise control (ACC) and for an engine management system (EMS). The simulation model allows processing of various sensors data like engine speed, engine temperature, and distance from the front vehicle. By collecting data from various sensors, ECU controls the vehicle speed by using electronic fuel injector actuator. ECU model simulates the failures to design a fault-tolerant system and controls the engine speed with the aid of an open loop control technique using EMS. ECU provides safety to the user by avoiding the collision by using IR Sensor and deployment of the air bags using MEMS accelerometer in the case of emergency using Adaptive Cruise Control (ACC). ECU mainly concentrates on functionality of fuel metering.This Simulation model could be used as a tool for swift development and test models of ECU in order to control the engine in laboratory for fuel economy and engine performance and safety improvement purposes for vehicles. The simulation has been realized using Simulink and Stateflow, which are components of Mathworks' MATLAB software.