Symptom Confirmation And Diagnostic Trouble Code

HINT:

• The diagnostic system in COROLLA 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 the COROLLA.
  Fig 1: Symptom Confirmation And Diagnostic Trouble Code Chart

  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 a check must be made on 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 systems that are operating normally. This would make more difficult to detect the problem area or to try to repair irrelevant areas. Therefore, always follow the procedures in the correct order and perform the DTC check.
• A flow chart showing how to proceed with 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, this chart indicates how to proceed either to the DTC troubleshooting or to the troubleshooting of the problem symptoms table.

1. DTC check 
2. Making a note and clear the DTCs 
3. Symptom confirmation 
   SYMPTOM CONFIRMATION
   
   

   a	Problem symptoms exist
   b	No problem symptoms exist

   1. a: Go to step   5 
   2. b: 
4. Simulation test using the symptom simulation methods 
5. DTC check 
   DTC CHECK
   
   

   a	DTC displayed
   b	Normal code displayed

   1. a: Troubleshooting of problem indicated by DTC 
   2. b: Go to next step. 
6. Symptom confirmation 
   DTC CHECK
   
   

   a	No problem symptoms exist
   b	Problem symptoms exist

   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: Go to next step. 

      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 it is a secondary problem).