Toyota Corolla (E120) 2002–2008 Repair Manual / Introduction / How to troubleshoot ecu controlled systems / Symptom confirmation and diagnostic trouble code

Toyota Corolla (E120): Symptom confirmation and diagnostic trouble code

Hint

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• 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.

System	Diagnostic trouble code check	Input signal check (sensor check)	Diagnostic test mode (active test)
Sfi system	(With check mode)
Abs with ebd system
Electronic controlled automatic transaxle [ect]	(With check mode)
Supplemental restraint system
Cruise control system

• 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 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.

1 Dtc check

2 Making a note and clear the dtcs

3 Symptom confirmation

	Problem symptoms exist
	No problem symptoms exist

A go to step 5

B

4 Simulation test using the symptom simulation methods

5 Dtc check

	Dtc displayed
	Normal code displayed

A troubleshooting of problem indicated by dtc

B

6 Symptom confirmation

	No problem symptoms exist
	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 .

A system normal

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 it is a secondary problem).