How To Proceed With Troubleshooting

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

Fig 1: Identifying How To Proceed With Troubleshooting Flow Chart

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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.

     Important Points in the Customer Problem Analysis 

     • What ----- Vehicle model, system name
     • When ----- Date, time, occurrence frequency
     • Where ----- Road conditions
     • Under what conditions? ----- Running conditions, driving conditions, weather conditions
     • How did it happen? ----- Problem symptoms

   (Sample) Supplemental restraint system check sheet. 

   Fig 2: Customer Problem Analysis Check Sheet

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2. SYMPTOM CONFIRMATION AND DIAGNOSTIC TROUBLE CODE CHECK 

   The diagnostic system in the LEXUS IS300 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 IS300.
     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 Deterent 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 

     Fig 3: Diagnostic Trouble Code Check Procedure Table

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     Taking into account the points on the previous page, 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.

3. SYMPTOM SIMULATION 

   The most difficult case in troubleshooting is when no problem symptoms occurring. In such cases, a thorough customer problem analysis must be carried out. Then simulate a simulation of the same or similar conditions and environment in which the problem occurred in the customer's vehicle should be carried out. No matter how much skill or experience a technician has, troubleshooting without confirming the problem symptoms will lead to something important in the repair operation being overlooked and lead to mistakes or delays in repairs.

   For example:

   With a problem that only occurs when the engine is cold, or occurs as result of vibration caused by road during driving, the problem can never be determined as long as the symptoms are being checked on stationary vehicle or a vehicle with a warmed-up engine.

   Vibration, heat or water penetration (moisture) is difficult to reproduce. The symptom simulation tests below are effected substitutes for the conditions and can be applied on a stationary vehicle.

   Important Points in the Symptom Simulation Test:

   In the symptom simulation test, the problem symptoms as well as problem area or parts must be confirmed. First, narrow down the possible problem circuits according to the symptoms. Then, connect the tester and carry out the symptom simulation test, judging whether the circuit being tested is defective or normal, and also confirming the problem symptoms at the same time. Refer to the problem symptoms table for each system to narrow down the possible causes of the symptom.

   Fig 4: Identifying Symptom Simulation Test Table (1 Of 2)

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