Electronic Circuit Inspection Procedure

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.

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 the connector, press firmly until you hear the lock close with a "click" sound.
5. If checking the connector with a TOYOTA electrical tester, check the connector from the backside (harness side) using a mini test lead.

Fig 1: Handling Connectors

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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 Connectors

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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

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1. If there is any dirt on the terminal, clean the contact point using an air gun or cloth. Never polish the contact point using sandpaper as the platings 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: Identifying Repair Method For Connector Terminal

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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 high temperature part, or rotating, moving, vibrating or sharp-edged parts. Avoid panel edges, screw tips and similar 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 Correct Method Of Wire Handling

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1. Disconnect connectors A and C and measure the resistance between them.

   See Fig 7.

   RESISTANCE SPECIFIED CONDITIONS
   
   

   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

   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.

   Fig 7: Measuring Resistance Between Connectors A And C

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

   See Fig 8.

   RESISTANCE SPECIFIED CONDITION
   
   

   Tester Connection	Specified Condition
   Connector A terminal 1 - Connector B1 terminal 1	Below 1 Ω
   Connector B2 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 A And C, And B2 And C

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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.

   With each connector still connected, measure the voltage between the body ground and these terminals (in this order): 1) terminal 1 of connector A at the ECU 5 V output terminal, 2) terminal 1 of connector B, and 3) terminal 1 of connector C.

   See Fig 9.

2. Example results:

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.

Fig 9: Measuring Voltages Between Connectors And Body Ground

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1. Disconnect connectors A and C and measure the resistance between terminals 1 and 2 of connector A and the body ground.

   See Fig 11.

   RESISTANCE SPECIFIED CONDITIONS
   
   

   Tester Connection	Specified Condition
   Connector A terminal 1 - Body ground	Below 1 Ω
   Connector A terminal 2 - Connector C terminal 2	10 kΩ or higher

   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.

   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.

   See Fig 12.

   RESISTANCE SPECIFIED CONDITIONS
   
   

   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 Between Terminal 1 Of Connector A And Body Ground, And Terminal 1 Of Connector B2 And Body Ground

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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 1 Ω 

   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 evidence of bending, corrosion or foreign material. Lastly, check the contact pressure of the female terminals.

Fig 14: Checking Ground Terminals On ECU Side And Wire Harness Side

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