HOW TO PROCEED WITH TROUBLESHOOTING
Carry out troubleshooting in accordance with the procedures on the following page. Here, only the basic procedures are shown. Details are provided in Diagnostics section, showing the most effective methods for each circuit. Confirm the troubleshooting procedures first for the relevant circuit before beginning troubleshooting of that circuit.
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- CUSTOMER PROBLEM ANALYSIS In troubleshooting, the problem symptoms must be confirmed accurately and all preconceptions must be cleared away in order to give an accurate judgment. To ascertain just what the problem symptoms are, it is extremely important to ask the customer about the problem and conditions at the time it occurred. Important Point in the Problem Analysis: The following 5 items are important points in the problem analysis. Past problems which are thought to be unrelated and the repair history, etc. may also help in some cases. So as much information as possible should be gathered and its relationship with the problem symptoms should be correctly ascertained for reference in troubleshooting. A customer problem analysis table is provided in the Diagnostics section for each system for your use. (Sample) Engine control system check sheet.
- SYMPTOM CONFIRMATION & DIAGNOSTIC TROUBLE CODE CHECK The diagnostic system in the MR2 fulfills various functions. The first function is the Diagnostic Trouble Code Check in which a malfunction in the signal circuits to the ECU is stored in code in the ECU memory at the time of occurrence, to be output by the 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 check functions, the problem areas can be narrowed down quickly and troubleshooting can be performed effectively. The diagnostic functions are incorporated in the following systems in the MR2. 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 procedures 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 in the next page. This flow chart shows how to utilize the diagnostic trouble code check effectively. Then by carefully checking the results, this chart indicates how to proceed either to diagnostic trouble code troubleshooting or to troubleshooting of the problem symptoms table.
- SYMPTOM SIMULATION The most difficult case in troubleshooting is that there are no problem symptoms occurring. In such cases, a thorough customer problem analysis must be carried out. Then simulate the same or similar conditions and environment in which the problem occurred in the customer's vehicle. No matter how much experience a technician has, or how skilled he may be, if he proceeds to troubleshoot without confirming the problem symptoms he will tend to overlook something important in the repair operation and make a wrong guess somewhere, which will only lead to a standstill. For example, for a problem which only occurs when the engine is cold, or for a problem which occurs due to vibration caused by the road during driving, etc., the problem can never be determined so long as the symptoms are confirmed with the engine hot condition or the vehicle at a standstill. Since vibration, heat or water penetration (moisture) is a likely cause for problem which is difficult to reproduce, the symptom simulation tests introduced here are effective measures in that the external causes are applied to the vehicle in a stopped condition. Important Points in the Symptom Simulation Test: In the symptom simulation test, the problem symptoms should, of course, be confirmed, but the problem area or parts must also be found out. To do this, narrow down the possible problem circuits according to the symptoms before starting this test and connect a tester beforehand. After that, 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 The inspection procedures are shown in the table below. This table permits efficient and accurate troubleshooting using the diagnostic trouble codes displayed in the diagnostic trouble code chart. Proceed with troubleshooting in accordance with the inspection procedures given in the diagnostic chart corresponding to the diagnostic trouble codes displayed. The engine diagnostic trouble code chart is shown below as an example.
- PROBLEM SYMPTOMS TABLE The suspected circuits or parts for each problem symptom are shown in the table below. Use this table to troubleshoot the problem when a "Normal" code is displayed in the diagnostic trouble code chart but the problem is still occurring. Numbers in the table indicate the inspection order in which the circuits or parts should be checked. HINT: When the problem is not detected by the diagnostic system even though the problem symptom is present, it is considered that the problem is occurring outside the detection range of the diagnostic system, or that the problem is occurring in a system other than the diagnostic system.
- CIRCUIT INSPECTION How to read and use each page is shown below.
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- CONNECTOR CONNECTION & TERMINAL INSPECTION For troubleshooting, diagnostic trouble code charts or problem symptom table are provided for each circuit with detailed inspection procedures on the following pages. When all the component parts, wire harnesses and connectors of each circuit except the ECU are found to be normal in troubleshooting, then it is determined that the problem is in the ECU. Accordingly, if diagnosis is performed without the problem symptoms occurring, refer to step 8 to replace the ECU. So always confirm that the problem symptoms are occurring, or proceed with inspection while using the symptom simulation method. The instructions "Check wire harness and connector" and "Check and replace ECU" which appear in the inspection procedure, are common and applicable to all diagnostic trouble codes. Follow the procedure outlined below whenever these instructions appear. OPEN CIRCUIT: This could be due to a disconnected wire harness, faulty contact in the connector, a connector terminal pulled out, etc. HINT: It is rarely the case that a wire is broken in the middle of it. Most cases occur at the connector. In particular, carefully check the connectors of sensors and actuators Faulty contact could be due to rusting of the connector terminals, to foreign materials entering terminals or a deformation of connector terminals. Simply disconnecting and reconnecting the connectors once changes the condition of the connection and may result in a return to normal operation. Therefore, in troubleshooting, if no abnormality is found in the wire harness and connector check, but the problem disappears after the check, then the cause is considered to be in the wire harness or connectors. SHORT CIRCUIT: This could be due to a contact between wire harness and the body ground or to a short circuit occurred inside the switch, etc. HINT: When there is a short circuit between the wire harness and body ground, check thoroughly whether the wire harness is caught in the body or is clamped properly.
- CONNECTOR HANDLING When inserting tester probes into a connector, insert them from the rear of the connector. When necessary, use mini test leads. For water resistant connectors which cannot be accessed from behind, take good care not to deform the connector terminals.
- CONTINUITY CHECK (OPEN CIRCUIT CHECK) Disconnect the connectors at both ECU and sensor sides. Measure the resistance between the applicable terminals of the connectors. Resistance: 1 ohm or less HINT: Measure the resistance while lightly shaking the wire harness vertically and horizontally.
- RESISTANCE CHECK (SHORT CIRCUIT CHECK) Disconnect the connectors on both ends. Measure the resistance between the applicable terminals of the connectors and body ground. Be sure to carry out this check on the connectors on both ends. Resistance: 1 Mohm or higher HINT: Measure the resistance while lightly shaking the wire harness vertically and horizontally.
- VISUAL CHECK & CONTACT PRESSURE CHECK Disconnect the connectors at both ends. Check for rust or foreign material, etc. in the terminals of the connectors. Check crimped portions for looseness or damage and check that the terminals are secured in lock portion. HINT: The terminals should not come out when pulled lightly from the back. Prepare a test male terminal and insert it in the female terminal, then pull it out. NOTE: When testing a gold-plated female terminal, always use a gold-plated male terminal. HINT: When the test terminal is pulled out more easily than others, there may be poor contact in that section.
- CHECK OPEN CIRCUIT For the open circuit in the wire harness in (Scheme 41), perform "(a) Continuity Check" or "(b) Voltage Check" to locate the section. Check the continuity. Disconnect connectors "A" and "C" and measure the resistance between them. In the case of (Scheme 42): Between terminal 1 of connector "A" and terminal 1 of connector "C" --> No continuity (open) Between terminal 2 of connector "A" and terminal 2 of connector "C" --> Continuity Therefore, it is found out that there is an open circuit between terminal 1 of connector "A" and terminal 1 of connector "C". Disconnect connector "B" and measure the resistance between the connectors. In the case of (Scheme 43): Between terminal 1 of connector "A" and terminal 1 of connector "B1" --> Continuity Between terminal 1 of connector "B2" and terminal 1 of connector "C" --> No continuity (open) Therefore, it is found out that there is an open circuit between terminal 1 of connector "B2" and terminal 1 of connector "C". Check the voltage. In a circuit in which voltage is applied (to the ECU connector terminal), an open circuit can be checked for by conducting a voltage check. (Scheme 44), with each connector still connected, measure the voltage between body ground and terminal 1 of connector "A" at the ECU 5 V output terminal, terminal 1 of connector "B", and terminal 1 of connector "C", in that order. If the results are: 5V: Between terminal 1 of connector "A" and body ground 5V: Between terminal 1 of connector "B" and body ground 0V: Between terminal 1 of connector "C" and body ground Then it is found out that there is an open circuit in the wire harness between terminal 1 of "B" and terminal 1 of "C".
- CHECK SHORT CIRCUIT If the wire harness is ground shorted as in (Scheme 45), locate the section by conducting a "continuity check with the body ground". Check the continuity with the body ground. Disconnect connectors "A" and "C" and measure the resistance between terminals 1 and 2 of connector "A" and the body ground. In the case of (Scheme 46): Between terminal 1 of connector "A" and body ground --> Continuity (short) Between terminal 2 of connector "A" and body ground --> No continuity Therefore, it is found out that there is a short circuit between terminal 1 of connector "A" and terminal 1 of connector "C". Disconnect connector "B" and measure the resistance between terminal 1 of connector "A" and body ground, and terminal 1 of connector "B2" and body ground. In the case of (Scheme 47): Between terminal 1 of connector "A" and body ground --> No continuity Between terminal 1 of connector "B2" and body ground --> Continuity (short) Therefore, it is found out that there is a short circuit between terminal 1 of connector "B2" and terminal 1 of connector "C".
- CHECK & REPLACE ECU First check the ECU ground circuit. If it is faulty, repair it. If it is normal, the ECU could be faulty. So replace the ECU with a normal functioning one and check If the symptoms appear. Measure the resistance between the ECU ground terminal and the body ground. Resistance: 1 ohm or less Disconnect the ECU connector, check the ground terminals on the ECU side and wire harness side for bend and check the contact pressure.