LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Toyota >> 2004 >> Matrix Base, FWD, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 381 (Introduction) >> How To Troubleshoot Ecu Controlled Systems >> Electronic Circuit Inspection Procedure
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Electronic Circuit Inspection Procedure

WARNING: This page is about a different car, the 2002 Toyota Highlander. 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:

      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. NOTE: Water proof connector cannot be checked from its back side, check by connecting the sub-harness.

      Do not damage the terminals moving the inserted tester needle.

    2. Handling of connectors:
      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.
        Fig 1: Identifying Correct Connector Handling Procedures
        G00397481Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      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, damaged and missing 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.
    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 pulling the wire harness lightly (missing terminal, terminal crimping condition, core wire break).
        Fig 2: Inspecting Terminal Ends
        G00397482Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
        3. NOTE: When testing a gold-plated female terminal, always use a gold-plated male terminal.
        Fig 3: Inspecting Contact Pressure
        G00397483Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      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.
    4. Repair method of connector terminal:
      1. In case there is any soil at the contact point, clean the contact point using an air gun or waste cloth. At this time, never polish the contact point using a sand paper as the plating may come off.
      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.
        Fig 4: Repairing Connector Terminals
        G00397484Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    5. Handling of wire harness:
      1. In case of removing the wire harness, check the wiring and clamping condition before proceeding the work, so that it is restored correctly.
      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, 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 vinyl tape.
  2. Continuity Check (Open Circuit Check): 
    NOTE: Measure the continuity while lightly shaking the wire harness vertically and horizontally.
    1. Disconnect the connectors at both ECU and sensor sides.
      Fig 5: Measuring Continuity (1 Of 2)
      G00372060Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Measure the resistance between the applicable terminals of the connectors. Resistance: One ohm or less.
      Fig 6: Measuring Continuity (2 Of 2)
      G00372061Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    3. NOTE: Measure the resistance while lightly shaking the wire harness vertically and horizontally.
  3. Resistance Check (Short Circuit Check): 
    1. Disconnect the connectors on both ends.
    2. Measure the resistance between the applicable terminals of the connectors and body ground. Be sure to carry out this check on the connectors on both ends. Resistance: One m/ohm or higher.
      Fig 7: Measuring Resistance
      G00372062Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  4. Visual Check And Contact Pressure Check: 
    NOTE:
    • The terminals should not come out when pulled lightly from the back.
      Fig 8: Inspecting Contact Pressure
      G00372063Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    • When testing a gold-plated female terminal, always use gold-plated male terminal.
    • When the test terminal is pulled out more easily than others, there may be poor contact in that section.
    1. Disconnect the connectors at both ends.
    2. Check for rust or foreign material, etc. in the terminals of the connectors.
    3. Check crimped portions for looseness or damage and check that the terminals are secured in lock portion.
    4. Prepare a test male terminal and insert it in the female terminal, then pull it out.
  5. Check Open Circuit:  For the open circuit in the wire harness, see Fig 9, perform " a Continuity Check" or " b Voltage Check" to locate the section.
    Fig 9: Checking For Open Circuit (1 Of 4)
    G00397408Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    1. Check the continuity:
      1. Disconnect connectors "A" and "C" and measure the resistance between them. In the case of Fig 10:
        1. Between terminal 1 of connector "A" and terminal 1 of connector "C", if no continuity (open).
        2. Between terminal 2 of connector "A" and terminal 2 of connector "C" means continuity.
          3. Fig 10: Checking For Open Circuit (2 Of 4)
          G00397409Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
        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 11:

        1. Between terminal 1 of connector "A" and terminal 1 of connector "B1" has continuity.
        2. Between terminal 1 of connector "B2" and terminal 1 of connector "C" there is no continuity (open).
          3. Fig 11: Checking For Open Circuit (3 Of 4)
          G00397410Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
        Therefore, it is found out that there is an open circuit between terminal 1 of connector "B2" and terminal 1 of connector "C".

    2. Check The Voltage: 

      In a circuit in which voltage is applied (to the ECU connector terminal), an open circuit can be checked for by conducting a voltage check.

      As shown in Fig 12, with each connector still connected, measure the voltage between body ground and terminal 1 of connector "A" at the ECU 5V output terminal, terminal 1 of connector "B", and terminal 1 of connector "C", in that order.

      Fig 12: Checking For Open Circuit (4 Of 4)
      G00397411Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      If the results are: 

      1. 5V: Between terminal 1 of connector "A" and body ground
      2. 5V: Between terminal 1 of connector "B" and body ground
      3. Zero 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 connector "B" and terminal 1 of connector "C".

  6. Check Short Circuit:  If the wire harness is shorted to ground as in Fig 13, locate the section by conducting a "continuity check with ground".

    Check the continuity with ground:

    1. Disconnect connectors "A" and "C" and measure the resistance between terminals 1 and 2 of connector "A" and body ground.
      Fig 13: Checking Short Circuit (1 Of 3)
      G00397412Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      In the case of Fig 14:

      1. Between terminal 1 of connector "A" and body ground there is continuity (short).
      2. Between terminal 2 of connector "A" and body ground there is NO continuity.
        3. Fig 14: Checking Short Circuit (2 Of 3)
        G00397413Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      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 body ground, and terminal 1 of connector "B2" and body ground.

      In the case of Fig 15:

      1. Between terminal 1 of connector "A" and body ground there is no continuity.
      2. Between terminal 1 of connector "B2" and body ground there is continuity (short).
        3. Fig 15: Checking Short Circuit (3 Of 3)
        G00397414Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      Therefore, it is found out that there is a short circuit between terminal 1 of connector "B2" and terminal 1 of connector "C".

  7. Check And Replace ECU:  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 that the symptoms disappear.
    1. Measure the resistance between the ECU ground terminal and the body ground.

      Resistance: One ohm or less  .

      Fig 16: Locating ECU Ground
      G00372065Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Disconnect the ECU connector, check the ground terminals on the ECU side and the wire harness side for bend and check the contact pressure.
      Fig 17: Locating ECU Ground (Wire Harness Side)
      G00372066Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
scientia non olet · About LEMON Manuals