Symptom Confirmation And Diagnostic Trouble Code

WARNING: This page is about a different car, the 2003 Toyota 4Runner. However, it is still accessible from the selected car via links, so may be relevant.

NOTE:

The diagnostic system in 4RUNNER 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 4RUNNER.

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 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 flow chart showing how to proceed with troubleshooting using the diagnostic trouble code (DTC) check is shown on the this page. 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.

DTC check
Making a note of the DTCs displayed
Symptom confirmation

Fig 2: Symptom Confirmation Chart
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
1. a : Go to step 5
2. b : Go To Next Step
Simulation test using symptom simulation methods
DTC check

Fig 3: DTC Check Chart
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
1. a : Troubleshooting of problem indicated by DTC
2. b : Go To Next Step
Symptom confirmation

Fig 4: Symptom Confirmation Chart
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 page 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).