Symptom Confirmation And Diagnostic Trouble Code

HINT:

• The diagnostic system in LEXUS GX470 has various functions. The first function is the Diagnostic Trouble Code (DTC) Check, in which a malfunction in the signal circuits to the ECU is stored in code form in the ECU memory. 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, it is possible to quickly narrow down potential problem areas and troubleshooting can be performed effectively. The diagnostic functions are incorporated in the following systems in LEXUS GX470.
  Fig 1: Diagnostic Table

  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
• 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 during the problem symptom check it must be checked 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 symptom confirmation to determine the current conditions. If this is not done, it may, depending on the case, result in unnecessary troubleshooting for normally operating systems, making it more difficult to detect the problem area, or in trying to repair irrelevant areas. Therefore, always follow the procedures in the correct order and perform the DTC check.
• A table showing how to proceed with troubleshooting using the diagnostic trouble code (DTC) check is shown in Fig 2. This table shows how to utilize the DTC check effectively. Then, by carefully checking the results, this table indicates how to proceed either to the DTC troubleshooting or to the troubleshooting of the PROBLEM SYMPTOMS TABLE .

1. DTC check 
   1. Go to next step.
2. Make a note of DTCs displayed and then clear the memory 
   1. Go to next step.
3. Symptom confirmation 
   Fig 2: Symptom Confirmation Table

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   1. A: Go to step   5 . 
   2. B: Go to next step. 
4. Simulation test using the symptom simulation methods 
   1. Go to next step.
5. DTC check 
   Fig 3: DTC Troubleshooting Table

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   1. A: Troubleshooting of problem indicated by DTC 
   2. B: Go to next step. 
6. Symptom confirmation 
   Fig 4: Symptom Confirmation Table

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   If a DTC is displayed in the initial DTC check, it indicates that a trouble may have occurred in a wire harness or connector in that circuit in the past. Therefore, check the wire harness and connectors (See ELECTRONIC CIRCUIT INSPECTION PROCEDURE  ).

   1. A: System normal 
   2. B: Troubleshooting of each problem symptom 

   The problem is still occurring in a place other than the diagnostic circuit (The DTC displayed first is either for a past problem or a secondary problem).