Toyota Sienna Service Manual: Check and replace ecu

Toyota Sienna Service Manual / Introduction / How to troubleshoot ecu controlled systems / Electronic circuit inspection procedure / Check and replace ecu

NOTICE: • 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.

(a) First, check the ECU ground circuit. If it is faulty, repair it. If it is normal, the ECU could be faulty.

Temporarily replace the ECU with a normally functioning one and check if the symptoms occur. If the trouble symptoms disappear, replace the original ECU.

Measure the resistance between the ECU ground terminal and body ground

(1) Measure the resistance between the ECU ground terminal and body ground.

Standard resistance: Below 1 Ω

Disconnect the ECU connector

(2) Disconnect the ECU connector. Check the ground terminal on the ECU side and wire harness side for bending, corrosion or foreign matter. Lastly, check the contact pressure of the female terminals.

Check for short circuit

(a) If the wire harness is ground shorted (Fig. 5), locate the section by conducting a resistance check with the body ground (below). (b) Check the resistance with the body ground. ...

How to proceed with troubleshooting

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