Automotive Troubleshooting Outline


With regards to the inspection for troubleshooting, besides the inspection method you have learned, a method to identify the malfunction location is needed. When you troubleshoot, combine several inspections to perform an estimation to fi nd the cause.
• Reproduction method
• Diagnostic inspection
• ECU data inspection
• Engine rotation resistance inspection
• Engine starting condition inspection
• Ignition, glow system inspection
• Fuel system inspection
• Compression system inspection
• Power balance inspection
• A/F inspection
• Oil loss via the piston rings/valve guides inspection
• Exhaust condition inspection
• Terminal contact pressure inspection
Troubleshooting Reproduction Method
The technician should perform the reproduction using a technique based on the conditions that result in the symptoms that the customer points out. Depending on the conditions in which the symptoms occur, the reproduction method should be performed by combining several techniques.
1. Apply vibration
2. Apply heat and/or cold
3. Apply water
4. Apply electrical load
During the procedure, if the connector is unintentionally disconnected or connected, the contact condition changes and the symptoms may not be reproduced. Until the symptoms are confi rmed by the reproduction, do not attempt to disconnect and connect the connector. The connector should not be disconnected and connected until the symptoms have been confi rmed and the technician can perform troubleshooting. If the symptoms are reproduced when the technician vibrates the wire harnesses, or heats or cools the parts, the cause can be judged to be there. In this case, perform the reproduction method while measuring the voltage to determine whether or not the malfunction occurs at the specifi ed voltage in order to determine the malfunction location.
Troubleshooting Reproduction Method
1. Apply vibration
Similar to when the vehicle vibrates to create a situation where the engine is inclined or the wire harness is pulled, vibrate the sensors and wire harnesses in order to reproduce the malfunction including poor contact.
Inspection method
• Parts and sensors
Lightly tap the parts and sensors with a fi nger in order to check whether or not the malfunction occurs.
For relays, the contacts will open when there is a strong impact. Therefore even if they are normal, a malfunction may occur.
• Wire harness and connector
Lightly swing the wire harnesses up and down or right and left to check for a malfunction. For the wire harness in particular, focus inspection on the base of the connectors, the fulcrum of the vibration and the through part of the body.
If the terminal is disconnected within the connector, carelessly pushing in the wire harness will connect the terminal, preventing the malfunction from being reproduced.
• Engine vibration
Malfunction of the wire harnesses in the engine compartment may occur when the engine is tilting due to torque reactive force. In an A/T vehicle, stalling an engine in the D or R range may reproduce the symptoms.
2. Apply heat or cold
To create a condition where parts expand or contract due to a temperature change, heat and cool the parts in order to reproduce poor contact or a short circuit.
Inspection method
Apply heat or cold to parts using a hair drier, spot air conditioner, refrigerator, and so on to check whether the malfunction occurs or not.
• Heat to a temperature where the technician can still touch by hand (approximately 60 degrees centigrade (140 degrees Fahrenheit) or less)
• Do not directly heat or cool the electronic parts by opening the lid of the ECU, etc.
3. Apply water
To create the conditions where water enters or condensation is produced in the connector, apply water to the vehicle in order to reproduce the malfunction, including poor contact or a short circuit.
Inspection method
Apply water to the vehicle in order to check whether the malfunction occurs or not.
• Do not directly apply water to the engine compartment, but spray the front of the radiator to indirectly apply moisture to the vehicle.
• Do not directly apply water to the electronic parts.
If rain leaks into the cabin, water may enter the ECU or connector through the wire harness. Therefore, this should be checked, especially if the vehicle has a history of leaks.
4. Apply electrical load
To create the conditions where the battery voltage drops or fluctuations occur, apply a large electrical load to reproduce the malfunction, including a voltage drop or fl uctuation.
Inspection method
Turn on all electrical devices, including heater blower, headlamp, rear window defogger to inspect for the malfunction.

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