Copyright Goodheart-Willcox Co., Inc. 415 After studying this chapter, you will be able to: ■ Perform a visual inspection of the computer, its sensors, actuators, and the systems they monitor and control. ■ Test sensors and their circuits. ■ Remove and replace sensors. ■ Test and replace actuators. ■ Remove and replace a computer. ■ Program an EEPROM. ■ Demonstrate safe working practices when servic- ing automotive computers. ■ Correctly answer ASE certification test questions on servicing computer system components. Since almost all vehicle systems now use computer components, you must have a thorough knowledge of computer circuit service methods. Otherwise, you will not fully understand the chapters on the service and repair of fuel injection, ignition, and emission control systems. This chapter will briefly summarize how to test computer components and circuits and help you develop the skills needed to verify where problems are. After you have checked the computer for trouble codes, you can find the exact source of the problem by doing pinpoint tests. Pinpoint tests are more specific tests of individual components. The service manual will normally explain how to do each pinpoint test. It will show specific tests, as well as provide com- ponent electrical values and other critical information. Remember that trouble codes only indicate the area of trouble and sometimes the type of problem, not what part or circuit is at fault. It is therefore impera- tive that you know how to do basic electrical tests on individual components. Preliminary Visual Inspection A preliminary visual inspection involves look- ing for signs of obvious trouble: loose wires, leaking vacuum hoses, part damage, etc. For example, if the trouble code says there is something wrong in the coolant temperature sensor circuit, you should check the sensor resistance and the wiring going to the sen- sor. You should also check the coolant level and the thermostat. A low coolant level or engine overheating could also set this code. Chapter 25 Computer System Service