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Electronic Circuit Inspection Procedure

  1. BASIC INSPECTION 
    1. WHEN MEASURING RESISTANCE OF ELECTRONIC PARTS
      1. Unless stated, all resistance measurements should be made at an ambient temperature of 20°C (68°F). Resistance measurements may be outside the specifications if measured at high temperatures, i.e. immediately after the vehicle has been running. Measurements should be made after the engine has cooled down.
    2. HANDLING CONNECTORS
      1. When disconnecting a connector, first squeeze the mating halves tightly together to release the lock, then press the lock claw and separate the connector.
      2. When disconnecting a connector, do not pull on the harnesses. Grasp the connector directly and separate it.
      3. Before connecting a connector, check that there are no deformed, damaged, loose or missing terminals.
      4. When connecting a connector, press firmly until you hear the lock close with a "click" sound.
      5. If checking a connector with a TOYOTA electrical tester, check the connector from the backside (harness side) using a mini test lead.
      NOTE:
      • As a waterproof connector cannot be checked from the backside, check by connecting a sub-harness.
      • Do not damage the terminals by moving the inserted tester needle.
      Fig 1: Checking Connector From Backside (Harness Side) Using Mini Test Lead
      G02974425Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    3. CHECKING CONNECTORS
      1. Checking when a connector is connected: Squeeze the connector together to confirm that it is fully connected and locked.
      2. Checking when a connector is disconnected: Check by pulling the wire harness lightly from the backside of the connector. Look for unlatched terminals, missing terminals, loose crimps or broken conductor wires.

        Check visually for corrosion, metallic or foreign objects and water; and bent, rusted, overheated, contaminated, and deformed terminals.

        NOTE: When testing a gold-plated female terminal, always use a gold-plated male terminal.
        Fig 2: Checking By Pulling Wire Harness
        G02974426Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      3. Checking the contact pressure of the terminal: Prepare a spare male terminal. Insert it into a female terminal, and check for ample tension when inserting and after full engagement.
        Fig 3: Checking Contact Pressure Of Terminal
        G02974427Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    4. REPAIR METHOD OF CONNECTOR TERMINAL
      1. If there is any dirt on the terminal, clean the contact point using an air gun or cloth. Never rub the contact point using sandpaper as the plating may come off.
      2. If there is abnormal contact pressure, replace the female terminal. If the male terminal is gold-plated (gold color), use a gold-plated female terminal; if it is silver-plated (silver color), use a silver-plated female terminal.
      3. Damaged, deformed, or corroded terminals should be replaced. If the terminal will not lock into the housing, the housing may have to be replaced.
        Fig 4: Repairing Method Of Connector Terminal
        G02974428Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    5. HANDLING OF WIRE HARNESS
      1. If removing a wire harness, check the wiring and clamping before proceeding so that it can be restored in the same way.
      2. Never twist, pull or slacken the wire harness more than necessary.
      3. The wire harness should never come into contact with a high temperature part, or rotating, moving, vibrating or sharp-edged parts. Avoid contact with panel edges, screw tips and other sharp items.
      4. When installing parts, never pinch the wire harness.
      5. Never cut or break the cover of the wire harness. If it is cut or broken, replace it or securely repair it with vinyl tape.
        Fig 5: Identifying Incorrect And Correct Wire Harness
        G02974429Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  2. CHECK OPEN CIRCUIT 
    1. For an open circuit in the wire harness in Fig 6, perform a resistance check (step b) or a voltage check (step  c).
      Fig 6: Checking Voltage Resistance Circuit
      G02974430Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Check the resistance.
      1. Disconnect connectors A and C and measure the resistance between them.

        Standard (See  Fig 7 ): 

        TESTER CONNECTION SPECIFICATION

        Tester Connection Specified Condition
        Connector A terminal 1 - Connector C terminal 1 10 kΩ or higher
        Connector A terminal 2 - Connector C terminal 2 Below 1 Ω
        Fig 7: Checking Resistance
        G02974431Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

        HINT:

        Measure the resistance while lightly shaking the wire harness vertically and horizontally.

        If your results match the examples above, an open circuit exists between terminal 1 of connector A and terminal 1 of connector C.

      2. Disconnect connector B and measure the resistance between the connectors.

        Standard (See  Fig 8 ): 

        TESTER CONNECTION SPECIFICATION

        Tester Connection Specified Condition
        Connector A terminal 1 - Connector B 1 terminal 1 Below 1 Ω
        Connector B1 terminal 1 - Connector C terminal 1 10 kΩ or higher

        If your results match the examples above, an open circuit exists between terminal 1 of connector B2 and terminal 1 of connector C.

        Fig 8: Measuring Resistance Between Connectors
        G02974432Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    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.

        See Fig 9:

        With each connector still connected, measure the voltage between the body ground and these terminals (in this order): 1) terminal 1 of connector A, 2) terminal 1 of connector B, and 3) terminal 1 of connector C.

        Example results: 

        Fig 9: Measuring Voltage Between Body Ground And Terminals
        G02974433Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
        TESTER CONNECTION SPECIFICATION

        Tester Connection Specified Condition
        Connector A terminal 1 - Body ground 5 V
        Connector B terminal 1 - Body ground 5 V
        Connector C terminal 1 - Body ground 0 V

        If your results match the examples above, an open circuit exists in the wire harness between terminal 1 of connector B and terminal 1 of connector C.

  3. CHECK SHORT CIRCUIT 
    1. If the wire harness is ground shorted (See Fig 10), locate the section by conducting a resistance check with the body ground (below).
      Fig 10: Checking Short Circuit
      G02974434Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Check the resistance with the body ground.
      1. Disconnect connectors A and C and measure the resistance.

        Standard (See  Fig 11 ): 

        TESTER CONNECTION SPECIFICATION

        Tester Connection Specified Condition
        Connector A terminal 1 - Body ground Below 1 Ω
        Connector A terminal 2 - Body ground 10 kΩ or higher
        Fig 11: Measuring Resistance
        G02974435Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

        HINT:

        Measure the resistance while lightly shaking the wire harness vertically and horizontally.

        If your results match the examples above, a short circuit exists between terminal 1 of connector A and terminal 1 of connector C.

      2. Disconnect connector B and measure the resistance.

        Standard (See  Fig 12 ): 

        TESTER CONNECTION SPECIFICATION

        Tester Connection Specified Condition
        Connector A terminal 1 - Body ground 10 kΩ or higher
        Connector B2 terminal 1 - Body ground Below 1 Ω

        If your results match the examples above, a short circuit exists between terminal 1 of connector B2 and terminal 1 of connector C.

        Fig 12: Measuring Resistance
        G02974436Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  4. CHECK AND REPLACE ECU 
    NOTE:
    • The connector should not be disconnected from the ECU. Perform the inspection from the backside of the connector on the wire harness side.
    • When no measuring condition is specified, perform the inspection with the engine stopped and the ignition switch ON.
    • Check that the connectors are fully seated. Check for loose, corroded or broken wires.
    1. First, check the ECU ground circuit. If it is faulty, repair it. If it is normal, the ECU could be faulty. Replace the ECU with a functioning one and check if the symptoms occur. If the trouble symptoms stop, replace the ECU.
      1. Measure the resistance between the ECU ground terminal and body ground.

        Standard: Below 1 Ω 

        Fig 13: Measuring Resistance Between ECU Ground Terminal And Body Ground
        G02974437Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      2. Disconnect the ECU connector. Check the ground terminals (on the ECU side and wire harness side) for evidence of bending, corrosion or foreign material. Lastly, check the contact pressure of the female terminals.
        Fig 14: Checking Ground Terminals
        G02974438Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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