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.
- 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.
- 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
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.
- 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.
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- DIAGNOSTIC TROUBLE CODE TABLE
This table permits efficient and accurate troubleshooting using the diagnostic trouble codes displayed in the diagnostic trouble code check. Proceed with troubleshooting in accordance with the inspection procedure given in the diagnostic chart corresponding to the diagnostic trouble codes displayed.
- PROBLEM SYMPTOMS TABLE
The suspected circuits or parts for each problem symptom are shown in the table below. Use this table to troubleshoot when, during a DTC check, a "Normal" code is displayed in the diagnostic trouble code check but the problem is still occurring. Numbers in the table show the inspection order in which the circuits or parts should be checked.
HINT:
In some cases, a problem is not detected by the diagnostic system even though a problem symptom is present. It is possible that the problem is occurring outside the detection range of the diagnostic system, or that the problem is occurring in a completely different system.
EXAMPLE OF PROBLEM SYMPTOM CHARTSymptom Suspect Area Engine does not crank (Does not start) 1. Starter & Starter relay No initial combustion (Does not start) 1. ECM power source circuit 2. Fuel pump control circuit 3. Engine Control Module (ECM) No complete combustion (Does not start) 1. Fuel pump control circuit Engine cranks normally (Difficult to start) 1. Starter signal circuit 2. Fuel pump control circuit 3. Compression Cold engine (Difficult to start) 1. Starter signal circuit 2. Fuel pump control circuit Hot engine 1. Starter signal circuit 2. Fuel pump control circuit Low idle speed (Poor idle) 1. A/C signal circuit (Compressor circuit) 2. Fuel pump control circuit - CIRCUIT INSPECTION