How To Proceed With Troubleshooting

Carry out troubleshooting in accordance with the procedure below. Only a basic procedure is shown. Details in the Diagnostics information show the most effective methods for each circuit. Confirm troubleshooting procedures first for the relevant circuit before beginning troubleshooting of that circuit.

Fig 1: Flow Chart For Proceed With Troubleshooting

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1. CUSTOMER PROBLEM ANALYSIS 
   • The 5 items in the table below are important points in the problem analysis:
   • In troubleshooting, the problem symptoms must be confirmed accurately. Preconceptions should be discarded in order to give an accurate judgement. To ascertain what the problem symptoms are, it is extremely important to ask the customer about the problem and the conditions at the time it occurred.
   Fig 2: Important Points In Customer Problem Analysis

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   (Sample) Supplemental restraint system check sheet. 

   Fig 3: Supplemental Restraint System Check Sheet

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2. SYMPTOM CONFIRMATION AND DIAGNOSTIC TROUBLE CODE CHECK 

   The diagnostic system in the LEXUS IS 300 fulfills various functions.

   • The first function is the Diagnostic Trouble Code (DTC) Check. In a DTC Check, a previous malfunction's DTC can be checked by a technician during troubleshooting. (A DTC is a code stored in the ECU memory whenever a malfunction in the signal circuits to the ECU occurs.)
   • 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, the problem areas can be narrowed down and troubleshooting is more effective. Diagnostic functions are incorporated in the following systems in the LEXUS IS 300.
   SYMPTOM CONFIRMATION AND DIAGNOSTIC TROUBLE CODE CHECK REFERENCE
   
   

   System	Diagnostic Trouble Code Check	Input Signal Check (Sensor Check)	Diagnostic Test Mode (Active Test)
   Engine	O (with Check Mode)	O	O
   Automatic Transmission	O (with Check Mode)	O
   ABS with EBD & BA & TRAC System	O	O	O
   ABS with EBD & BA & TRAC & VSC System	O	O	O
   Supplemental Restraint System	O
   Theft Deterrent System			O
   Cruise Control System	O	O
   Engine Immobilizer System	O
   Combination Meter System			O
   Body Control System			O
   Multiplex Communication System	O		O
   LEXUS Navigation System			O
   Air Conditioning System	O		O

   In diagnostic trouble code check, it is very important to determine whether the problem indicated by the diagnostic trouble code is still occurring or occurred in the past but returned to normal at present. In addition, it must be checked in the problem symptom check whether the malfunction indicated by the diagnostic trouble code is directly related to the problem symptom or not. For this reason, the diagnostic trouble codes should be checked before and after the symptom confirmation to determine the current conditions, as shown in the table below. If this is not done, it may, depending on the case, result in unnecessary troubleshooting for normally operating systems, thus making it more difficult to locate the problem, or in repairs not pertinent to the problem. Therefore, always follow the procedure in correct order and perform the diagnostic trouble code check.

   DIAGNOSTIC TROUBLE CODE CHECK PROCEDURE 

   A flow chart showing how to proceed with troubleshooting using the diagnostic trouble code check is shown below. This flow chart shows how to utilize the diagnostic trouble code check effectively, then by carefully checking the results, indicates how to proceed either to diagnostic trouble code troubleshooting or to troubleshooting of problem symptoms table.

   Fig 4: Diagnostic Trouble Code And Problem Condition

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