How To Proceed With Troubleshooting
Carry out the basic troubleshooting procedure shown in Fig 1 . Details in the Diagnostics area 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 important points in the problem analysis are shown in Fig 2
- 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.
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
(Sample) Supplemental restraint system check sheet.
- SYMPTOM CONFIRMATION AND DIAGNOSTIC TROUBLE CODE CHECK
The diagnostic system in the ECHO 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 ECHO shown in Fig 4.
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 Fig 5 .
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 in the correct order listed in Fig 5.
DIAGNOSTIC TROUBLE CODE CHECK PROCEDURE
Taking into account the points in the previous information, a flow chart showing how to proceed with troubleshooting using the diagnostic trouble code check is shown in Fig 6 . Directions from the flow chart will indicate how to proceed to DTC troubleshooting or to the troubleshooting of problem symptoms table.
- SYMPTOM SIMULATION
The most difficult case in troubleshooting is when no problem symptoms occur. 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 are effected substitutes for the conditions and can be applied on a stationary vehicle. Fig 7
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.
- DIAGNOSTIC TROUBLE CODE CHART
Use Diagnostic Trouble Codes (DTCs) to determine the trouble area and proper inspection procedure. For example, see "ENGINE PERFORMANCE" - DIAGNOSTIC TROUBLE CODE TABLE
- PROBLEM SYMPTOMS TABLE
The suspected circuits or parts for each problem symptom are shown in EXAMPLE OF PROBLEM SYMPTOM CHART . 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.
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 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.
- CIRCUIT INSPECTION
How to use this information is shown below.
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002