Symptom Confirmation And Diagnostic Trouble Code

HINT:

The diagnostic system in the LEXUS SC430 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 SC430:

  DIAGNOSTIC FUNCTIONS
  
  

  System	Diagnostic Trouble Code Check	Input Signal Check (Sensor Check)	Diagnostic Test Mode (Active Test)
  SFI System	X (with Check Mode)	X	X
  Tire Pressure Warning System	X	-	-
  ABS with EBD & BA & TRAC & VSC System	X	X	X
  Electronically Controlled Automatic Transmission [ECT]	X (with Check Mode)	X	-
  Power Tilt and Power Telescopic Steering Column	X	-	-
  Progressive Power Steering System	X	-	-
  Air Conditioning System	X	X	X
  Supplemental Restraint System	X	-	-
  Lighting System	X	-	-
  Audio System	X	-	-
  LEXUS Navigation System	X	-	-
  LEXUS Link System	X	-	-
  Power Window Control System	X	-	-
  Power Mirror Control System	X	-	-
  Power Door Lock Control System	X	X	-
  Wireless Door Lock Control System	X	X	-
  Key Reminder Warning System	X	-	-
  Engine Immobilizer System	X	-	-
  Theft Deterrent System	X	-	X
  Retractable Hardtop System	X	X	-
  Multiplex Communication System	X	-	-
  Cruise Control System	X	X	-

• 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 conditions, as shown in the SYMPTOM CONFIRMATION  .

  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 above in the correct order.

• A flow chart showing how to proceed with troubleshooting using the DTC check is shown below. Directions from the flow chart will indicate should be performed DTC troubleshooting or to the troubleshooting of each problem symptom.

1. DTC CHECK 
2. MAKE A NOTE OF DTCS DISPLAYED AND THEN CLEAR THE MEMORY 
3. SYMPTOM CONFIRMATION 
   SYMPTOM CONFIRMATION
   
   

   a	Symptoms exist
   b	No symptoms exist

   1. Go to step   5 
   2. Go to next step 
4. SIMULATION TEST USING THE SYMPTOM SIMULATION METHODS 
5. DTC CHECK 
   DTC CHECK
   
   

   a	DTC displayed
   b	No DTC displayed

   1. Troubleshooting of problem indicated by DTC 
   2. Go to next step 
6. SYMPTOM CONFIRMATION 
   SYMPTOM CONFIRMATION
   
   

   a	No symptoms exist
   b	Symptoms exist

   If a DTC was displayed in the initial DTC check, it indicates that the trouble 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 ).

   1. SYSTEM NORMAL 
   2. 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).