Symptom Confirmation And Diagnostic Trouble Code

HINT:

The diagnostic system in the LEXUS LS430 has various functions.

• The first function is the Diagnostic Trouble Code (DTC) check. A DTC is a code stored in the ECU memory whenever a malfunction in the signal circuits to the ECU occurs. In a DTC check, a previous malfunction's DTC can be checked by a technician during troubleshooting.
• Another function is the Input Signal Check, which checks if the signals from various switches are sent to the ECU correctly.

  By using these functions, the problem areas can be narrowed down and troubleshooting is more effective. Diagnostic functions are incorporated in the following systems in the LEXUS LS430:

  Fig 1: Diagnostic Trouble Code Chart

  Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
• In the DTC check, it is very important to determine whether the problem indicated by the DTC is: 1) still occurring, or 2) occurred in the past but has since returned to normal. In addition, the DTC should be compared to the problem symptom to see if they are related. For this reason, DTCs should be checked before and after confirmation of symptoms (i.e., whether or not problem symptoms exist) to determine current system conditions, as shown in the flowchart below.

  Never skip the DTC check. Failure to check DTCs may, depending on the case, result in unnecessary troubleshooting for systems operating normally or lead to repairs not pertinent to the problem. Follow the procedures listed in the flowchart in the correct order.

• A flowchart showing how to proceed with troubleshooting using the DTC check is shown below. Directions from the flowchart will indicate how to proceed either to DTC troubleshooting or to the trouble-shooting of the problem symptoms.

1. DTC CHECK 

   NEXT 

2. MAKE A NOTE OF DTCS DISPLAYED AND THEN CLEAR MEMORY 

   NEXT 

3. SYMPTOM CONFIRMATION 
   RESULT REFERENCE
   
   

   Result	Proceed to
   Symptoms exist	B
   No symptoms exist	A

   B Go to step   5 

   A: GO TO NEXT STEP 

4. SIMULATION TEST USING SYMPTOM SIMULATION METHODS 

   NEXT 

5. DTC CHECK 
   RESULT REFERENCE
   
   

   Result	Proceed to
   DTC is output	B
   DTC is not output	A

   B TROUBLESHOOTING OF PROBLEM INDICATED BY DTC 

   A: GO TO NEXT STEP 

6. SYMPTOM CONFIRMATION 
   RESULT REFERENCE
   
   

   Result	Proceed to
   Symptoms exist	B
   No symptoms exist	A

   If a DTC was displayed in the initial DTC check, the problem may have occurred in a wire harness or connector in that circuit in the past. Check the wire harness and connectors (see ELECTRONIC CIRCUIT INSPECTION PROCEDURE  ).

   B SYSTEM NORMAL 

   A: GO TO NEXT STEP 

7. 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).