Chapter 25 Computer System Service 427 Copyright Goodheart-Willcox Co., Inc. Depending on the manufacturer, it may be necessary to turn the ignition switch on or off during the connection and programming procedure. Double- check any instructions on ignition switch position before making any connections or beginning the programming procedure. The next step is to determine the type of programming that is needed. Programming a New Computer If a new computer is being installed, program only that computer. In many cases, other on-board comput- ers can be accessed and programmed using the data link connector. While most computers have internal cir- cuitry that protects them from accidental programming, be careful not to program the wrong computer. Do not attempt to program a new computer with information from the old computer or a computer from another vehicle. Any attempt to do this will set a failed program- ming sequence code in the new computer’s memory. Tech Tip In some cases, an erasure must be performed on a new computer before initial programming can take place. Reprogramming a Computer Computer reprogramming is often needed to solve specific performance or emission related problems. The auto manufacturer will put out a bulletin and provide the modified software to fix vehicle malfunctions. Before reprogramming a vehicle’s computer, determine the date that the current programming was downloaded or check the program’s calibration number. If the current program is the latest version, no further actions are required. If the latest program has not been downloaded, proceed with the reprogramming sequence. Before reprogramming most computers, you must first erase the existing information. After this step is complete, select the updated calibration information from the programming computer or scan tool menu. Then download the new information into the computer. On some systems, the erasure step is not necessary since the programming computer or scan tool will erase or overwrite the old information as it loads the new program into the computer. Tech Tip If the computer does not accept the new program or cannot be programmed, check all connections first. Ensure that the correct computer is being repro- grammed with the proper information and that all procedures are being followed. If the computer still cannot be programmed, it may need to be replaced. Allow sufficient time for the programming to take place. Monitor the computer or scan tool to determine when the programming sequence is complete. Do not touch any connections until you are sure the A B Goodheart-Willcox Publisher Figure 25-12. Most dealerships now have a dedicated laptop computer for EEPROM reprogramming. A—The laptop is plugged into the diagnostic link so it can download new information into the vehicle’s computer. B—Icons on the laptop screen allow the technician to select the correct software for downloading.