Electronic Circuit Inspection Procedure

BASIC INSPECTION
1. RESISTANCE MEASURING CONDITION OF ELECTRONIC PARTS
  1. Unless stated, all resistance is measured at an ambient temperature of 20°C (68°F). As the resistance may be outside the specifications if measured at high temperatures immediately after the vehicle has been running, measurements should be made when the engine has cooled down.
2. HANDLING OF CONNECTOR
  1. When removing the connector with lock, press the connector in the direction of the engagement and remove the lock by lightly pressing the lock claw.
  2. When removing the connector, do not hold the harness, but hold the connector.
  3. Before connecting the connector, check that there is no deformation, damage or missing terminals.
  4. The connector with a lock should be securely connected until it makes a "click" sound.
  5. When checking the connector with a Toyota electrical tester, check it from the backside (harness side) of the connector using a mini test lead.
    NOTE:
    As a water proof connector cannot be checked from the backside, check by connecting the sub-harness.
    
    Do not damage the terminals by moving the inserted tester needle.
    
    Fig 1: Removing Connector
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3. CONNECTOR CHECKING POINTS
  1. Checking when the connector is connected:
    By holding the connector, check the inserted condition and locking efficiency (engaged condition).
  2. Checking when the connector is removed:
    Check by lightly pulling the wire harness (missing terminal, terminal crimping condition, core wire break).
    
    Check visually for is any rust, metal particles, water and bent terminals (rust, mixing of foreign object, terminal deformation).
    
    NOTE: When testing a gold-plated female terminal, always use a gold-plated male terminal.
    
    Fig 2: Checking Lightly Pulling Wire Harness
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  3. Checking of the contact pressure of the terminal: Prepare a spare male terminal.
    Insert it into a female terminal, check the engaged condition and sliding resistance.
    
    Fig 3: Inserting Female Terminal
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4. REPAIR METHOD OF CONNECTOR TERMINAL
  1. If there is on the contact point, clean the contact point using an air gun or shop rag. However, never polish the contact point using sand paper as the platings may come off.
  2. In case of abnormal contact pressure, replace the female terminal. However, if a male terminal is gold-plated (gold color), use gold-plated female terminal and if it is silver-plated (silver color), use silver-plated female terminal.
    
    Fig 4: Identifying Repair Method Of Connector Terminal
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5. HANDLING OF WIRE HARNESS
  1. When removing the wire harness, check the positioning of the wiring and clamping before starting work in order to be able to restore it correctly.
  2. Never twist, pull or loosen the wire harness more than necessary.
  3. Never allow the wire harness to come into contact with a high-temperature, rotating, moving, vibrating or sharp (edge of the panel, tip of the screw, etc.) part.
    
    Fig 5: Identifying Handling Of Wire Harness Wrong Position
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  4. When installing parts, never let the wire harness be interfered with.
  5. Never cut or break the cover of the wire harness. If one is cut or broken, replace it or securely repair it with electrical tape.
CHECK OPEN CIRCUIT
1. For the open circuit in the wire harness in Fig 6, perform a continuity check in step (b) or a voltage check in step ( c) to locate the section.
  
  Fig 6: Circuit Diagram
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2. Check the continuity.
  1. Disconnect connectors A and C and measure > resistance between them.
    Resistance: 1 Ω or less
    
    HINT:
    
    Measure the resistance while lightly shaking the wire harness vertically and horizontally.
    
    In the case of Fig 7:
    
    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, the cause is an open circuit between terminal 1 of connector A and terminal 1 of connector C.
    
    Fig 7: Measuring Resistance Connectors A And C
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  2. Disconnect connector B and measure the resistance between the connectors.
    In the case of Fig 8:
    
    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, the cause is an open circuit between terminal 1 of connector B2 and terminal 1 of connection C.
    
    Fig 8: Disconnecting Connector B And Measuring Resistance Between Connectors
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3. Check the voltage.
  1. In a circuit in which voltage is applied (to the ECU connector terminal), an open circuit can be checked by conducting a voltage check.
    As shown in Fig 9, with each connector still connected, measure the voltage between the 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.
    
    Fig 9: Measuring Voltage Between Body Ground And Terminal 1 Of Connector A ECU 5 V Output Terminal
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  2. If the results are:
    5 V: Between terminal 1 of connector A and body ground
    
    5 V: Between terminal 1 of connector B and body ground
    
    0 V: Between terminal 1 of connector C and body ground
    
    Therefore, the cause is an open circuit in the wire harness between terminal 1 of connector B and terminal 1 of connector C.
CHECK SHORT CIRCUIT
1. If the wire harness is ground shorted as shown in Fig 10, locate the section by conducting a continuity check with the body ground in step (b).
  
  Fig 10: Checking Short Circuit
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2. Check the continuity with the body ground.
  1. Disconnect connectors A and C and measure the resistance between terminals 1 and 2 of connector A and the body ground.
    Resistance: 10 kΩ or higher
    
    HINT:
    
    Measure the resistance while lightly shaking the wire harness vertically and horizontally.
    
    In the case of Fig 11:
    
    Between terminal 1 of connector A and body ground --> Continuity (short)
    
    Between terminal 2 of connector A and body ground --> No continuity
    
    Therefore, the cause is a short circuit between terminal 1 of connector A and terminal 1 of connector C.
    
    Fig 11: Measuring Resistance Between Terminals 1 And 2 Of Connector A And Body Ground
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  2. Disconnect connector B and measure the resistance between terminal 1 of connector A and the body ground, and terminal 1 of connector B2 and the body ground.
    In the case of Fig 12:
    
    Between terminal 1 of connector A and body ground --> No continuity
    
    Between terminal 1 of connector B2 and body ground --> Continuity (short)
    
    Therefore, the cause is a short circuit between terminal 1 of connector B2 and terminal 1 of connector C.
    
    Fig 12: Measuring Resistance Between Terminal 1 Of Connector A And Body Ground
    Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
CHECK AND REPLACE ECU
NOTE:
- Start an inspection of the connector from the basic side of the connector on the wire harness side with the connector connected to the ECU.
- When no measurement condition is specified, perform the inspection with the engine stopped and also the ignition switch ON.
1. First check the ECU ground circuit. If it is faulty, repair it. If it is normal, the ECU could be faulty. In this case, replace the ECU with one that functions normally and check if the symptoms appear.
  1. Measure the resistance between the ECU ground terminal and body ground.
    Resistance: 1 Ω or less
    
    Fig 13: Measuring Resistance Between ECU Ground Terminal And Body Ground
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  2. Disconnect the ECU connector, check the ground terminals on the ECU side and wire harness side for bends and check the contact pressure.
    
    Fig 14: Disconnecting ECU Connector
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