Symptom Confirmation And Diagnostic Trouble Code Check

The diagnostic system in the Highlander fulfills various functions. The first function is the Diagnostic Trouble Code Check in which a malfunction in the signal circuits to the ECU is stored in code in the ECU memory at the time of occurrence, to be output by the technician during troubleshooting. Another function is the Input Signal Check which checks if the signals from various switches are sent to the ECU correctly. By using these check functions, the problem areas can be narrowed down quickly and troubleshooting can be performed effectively. Diagnostic functions are incorporated in the following systems.

Fig 1: Identifying Systems With Incorporated Diagnostic Functions

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• In the DTC check, it is very important to determine whether the problem indicated by the DTC is still occurring or has occurred in the past but returned to normal at present. In addition, it must be checked in the problem symptom check whether the malfunction indicated by the DTC is directly related to the problem symptom or not. For this reason, the DTC should be checked before and after the symptom confirmation to determine the current conditions. If this is not done, it may, depending on the case, result in an unnecessary troubleshooting for normally operating systems, making it more difficult to detect the problem area, or trying to repair irrelevant areas. Therefore, always follow the procedure in the correct order and perform the DTC check.
• A flow chart showing how to proceed with the troubleshooting using the diagnostic trouble code DTC check is shown below. This flow chart shows how to utilize the DTC check effectively, then by carefully checking the results, indicates how to proceed either to the DTC troubleshooting or to the troubleshooting of problem symptoms table.
  Fig 2: Identifying DTC Validation Procedure

  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002