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Electronic Circuit Inspection Procedure

WARNING: This page is about a different car, the 2004 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 68°F (20°C). Resistances measured 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 the 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 the connector with a TOYOTA electrical tester, check it from the backside (harness side) of the connector using a mini test lead.
        Fig 1: Identifying Handling Connectors
        G02833150Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      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.
    3. CHECKING CONNECTORS
      1. Checking when the connector is connected: Squeeze the connector together to confirm that it is fully inserted and locked.
      2. Checking when the 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.

        Fig 2: Checking Connectors
        G02833151Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
        NOTE: When testing a gold-plated female terminal, always use a gold-plated male terminal.
      3. Checking the contact pressure of the terminal: Prepare a spare male terminal. Insert it into a female terminal, and check for good tension when inserting and after full engagement.
        Fig 3: Checking Contact Pressure Of Terminal
        G02833152Courtesy 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 shop rag. Never polish the contact point using a sandpaper as the platings may come off.
        Fig 4: Cleaning Contact Point
        G02833153Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      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.
    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.
        Fig 5: Handling Of Wire Harness
        G02833154Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      3. The wire harness should never come into contact with high temperature parts, rotating, moving, vibrating or sharp-edged parts. Avoid 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.
  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 Open Circuit
      G02833155Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Check the resistance.
      1. Disconnect connectors A and C and measure the resistance between them.
        Fig 7: Checking Resistance Between Connectors A & C
        G02833156Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

        Resistance: Below 1Ω 

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

        Fig 7:

        Between terminal 1 of connector A and terminal 1 of connector C --> 10 kΩ or higher

        Between terminal 2 of connector A and terminal 2 of connector C --> Below 1Ω

        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.

        Fig 8:

        Between terminal 1 of connector A and terminal 1 of connector B1 --> Below 1Ω

        Between terminal 1 of connector B2 and terminal 1 of connector C --> 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: Checking Resistance Between Other Connectors
        G02833157Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    3. Check the voltage.
      Fig 9: Checking Voltage
      G02833158Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      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.

        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.

      2. Example results:

        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

        If your results match the examples above, an open circuit exists 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 (Fig 10), locate the section by conducting a resistance check with the body ground (below).
      Fig 10: Checking Short Circuit
      G02833159Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Check the resistance 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 

        Fig 11: Checking Resistance With Body Ground
        G02833160Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
        NOTE: Measure the resistance while lightly shaking the wire harness vertically and horizontally.

        Fig 11:

        Between terminal 1 of connector A and body ground --> Below 1 Ω.

        Between terminal 2 of connector A and body ground --> 10 kΩ. or higher

        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 between terminal 1 of connector A and the body ground, and terminal 1 of connector B2 and the body ground.

        Fig 12:

        Between terminal 1 of connector A and body ground --> 10 kΩ. or higher

        Between terminal 1 of connector B2 and body ground --> Below 1Ω.

        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: Checking Resistance Between Terminals & Body Ground
        G02833161Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  4. CHECK AND REPLACE ECU 
    NOTE:
    • Start the inspection of a connector from the backside of the connector (wire harness side) with the connector connected to the ECU
    • 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.

        Resistance: Below 1Ω 

        Fig 13: Measuring Resistance Between ECU Ground Terminal & Body Ground
        G02833162Courtesy 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 Terminals
        G02833163Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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