Automotive Troubleshooting Diagnostic


Diagnostic Inspection
To efficiently proceed with troubleshooting, use diagnostic codes in order to identify the malfunctioning area. The following are judged by identifying the codes.
• When DTC is displayed
The sensors, actuators, wiring and ECUs in the systems indicated by the malfunction codes may have a malfunction.
• When normal DTC is displayed
Systems that have a diagnostic function can be judged normal. Therefore, the malfunction may be in the systems that have no diagnostic function so proceed to this inspection.

The systems that have no diagnostic function include the ignition secondary system, fuel system, etc.
• When No DTC is displayed
The ECUs themselves do not operate or the power source system of the ECU has a malfunction.

Check mode
In normal mode, if a malfunction only momentarily occurs, it cannot be detected because it does not satisfy the diagnostic conditions. By switching into check mode, malfunction which occur momentarily, such as poor contact, can be detected.
Diagnostic Inspection
Purpose of inspection
Check whether the identifi ed diagnostic code accords with the actual malfunction symptoms. The malfunction systems that the code indicates may not accord with the system that actually indicates the malfunction.
Inspection method
(1) Inspect the diagnostic code and freeze frame data and record them.
(2) Clear the diagnostic code and reproduce the malfunction symptoms based on
diagnostic questioning.
To judge whether the displayed code when the vehicle was brought in is caused by a current malfunction or past malfunction, clear the displayed code once and then perform the reproduction test.
(3) Identify the diagnostic code again and judge whether the code is related to the malfunction or not.
• If the same code is displayed, it can be judged that the malfunction currently occurs in the system that the code indicates.
• If a code that is not related to the malfunction is displayed, or a normal code is displayed, the current malfunction is caused by something else. Therefore, perform troubleshooting appropriate for the malfunction symptoms.

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