By nature, automotive electronic systems are susceptible to Electromagnetic Interference (EMI). Devices capable of suppressing EMI have become an integral part of the automotive electronic system design. Methods of testing these devices individually and as part of the total electronic system have been developed and used as a design tool by the engineer. These methods range from individual component tests to total electronic system analysis and cover such areas as radiated noise susceptibility and the effects of electrical transients on the electronic system.The ability to test components in the laboratory allows the engineer to assemble reliable subsystems from which a total electronic system may be designed. Components and subsystems may be tested using a TEM cell, anechoic chamber and/or direct injection of noise signals. Computer control of the test provides repeatable results and better turn-around time than can be obtained by manual testing.This paper will present different methods of performing Electromagnetic Compatibility testing on components and electrical subsystems. Procedures for characterizing susceptibility to EMI will be reviewed and its applicability to the design process will be discussed. Case histories will be included to illustrate the advantages of component and subsystem testing to total vehicle analysis.