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Electronic Circuit Inspection Procedure

WARNING: This page is about a different car, the 2003 Toyota 4Runner. However, it is still accessible from the selected car via links, so may be relevant.
  1. 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). Because 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 a lock, press the connector toward the engagement and remove the lock by making the lock claw movable easily.
      2. When removing the connector, do not hold the harness, but hold the connector.
      3. Before connecting the connector, check that there are no deformation, damage and missing of the terminals.
      4. Connection of the connector with a lock should be securely done until it makes a click sound.
      5. In case of checking the connector with a Toyota electrical tester, perform it at the back side (harness side) of the connector using a mini test lead.
      Fig 1: Identifying Correct And Wrong Method Of Removing Connector
      G02814460Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      NOTE:
      • As a water proof connector cannot be checked from its back side, check by connecting the sub-harness.
      • Do not damage the terminals by moving the inserted tester needle.
    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. NOTE: When testing a gold-plated female terminal, always use a gold-plated male terminal.
        Fig 2: Checking Connector Harness
        G02814461Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      2. Checking when the connector is removed:

        Check by pulling the wire harness lightly (missing terminal, terminal crimping condition, core wire break).

        Check visually if there is any rust, metal tip, water and bend of terminal (rust, mixing of foreign object, terminal deformation).

      3. Checking of the contact pressure of the terminal: Prepare the same terminal as a male terminal. By inserting it to a female terminal, check the engaged condition and sliding load.
        Fig 3: Checking Engaged Condition And Sliding Load Of Terminal
        G02814462Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    4. REPAIR METHOD OF CONNECTOR TERMINAL
      1. In case that there is any soil at the contact point, clean the contact point using an air gun or shop rag. At this time, never polish the contact point using a sand paper as the platings may come off.
        Fig 4: Identifying Correct Method Of Repairing Connector Terminal
        G02814463Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      2. In case of abnormal contact pressure, replace the female terminal. At this time, if a male terminal is gold-plated (gold color), use gold-plated female terminals and if it is silver-plated (silver color), use silver-plated female terminals.
    5. HANDLING OF WIRE HARNESS
      1. In case of removing the wire harness, check the wiring and clamping condition before the work so as to is restore it correctly.
        Fig 5: Identifying Correct Method Of Handling Wire Harness
        G02814464Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      2. Never twist, pull or slack off the wire harness more than necessary.
      3. Never make the wire harness come into contact with a high-temperature part, rotating, moving, vibrating or acute-angled part (edge of the panel, tip of the screw, etc.).
      4. When installing parts, never sandwich the wire harness between them.
      5. Never cut or break the cover of the wire harness. If it is cut or broken, replace it or securely repair it with a vinyl tape or the like.
  2. CHECK OPEN CIRCUIT 
    1. For the open circuit in the wire harness in Fig 6, perform "(b) Check the continuity" or "(c) Check the voltage" to locate the section.
      Fig 6: Checking Open Circuit
      G02814465Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Check the continuity.
        NOTE:

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

        Fig 7: Measuring Resistance Between Connector A And C
        G02814466Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      1. Disconnect connectors "A" and "C" and measure the resistance between them.

        Resistance: 1 Ω or less 

        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, it is found out that there is an open circuit between terminal 1 of connector "A" and terminal 1 of connector "C".

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

        In the case of Fig 8:

        Fig 8: Measuring Continuity Between Terminals
        G02814467Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

        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".

    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: Checking Voltage
        G02814468Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      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

        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".

  3. CHECK SHORT CIRCUIT 
    1. If the wire harness is ground shorted as in Fig 10, locate the section by conducting a "continuity check with the body ground".
      Fig 10: Checking Short Circuit
      G02814469Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Check the continuity with the body ground.
      1. Disconnect connectors "A" and "C" and measure the resistance between terminal 1 and 2 of connector "A" and the body ground.

        Resistance: 1 MΩ or higher 

        NOTE:

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

        In the case of Fig 11:

        Fig 11: Checking Continuity With Body Ground (1 Of 2)
        G02814470Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

        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".

      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:

        Fig 12: Checking Continuity With Body Ground (2 Of 2)
        G02814471Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

        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".

  4. CHECK AND REPLACE ECU 
      NOTE:
      • Start an inspection of the connector from the backside of the connector on the wire harness side with the connector connected to the ECU.
      • When no measuring condition is specified, perform the inspection with the engine stopped and also the ignition switched ON.
    1. 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.
      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
        G02814472Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      2. Disconnect the ECU connector, check the ground terminals on the ECU side and wire harness side for bend and check the contact pressure.
        Fig 14: Identifying ECU Side And W/H Side Ground Terminal
        G02814473Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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