Ensure ignition is off. Locate ECT sensor. See ENGINE COOLANT TEMPERATURE (ECT) SENSOR LOCATION table. Remove ECT sensor.
Place probe end of ECT sensor and thermometer in container of water. Attach ohmmeter between ECT sensor terminals. Heat water and note that resistance is within specification in relation to temperature. See Fig 1. Replace ECT sensor if resistance is not within specification.
Using NEW gasket, install ECT sensor. Tighten ECT sensor to 15 ft. lbs. (20 N.m). Fill cooling system.

ENGINE COOLANT TEMPERATURE (ECT) SENSOR LOCATION

Model	Location
GS300	Left Front Of Cylinder Head & Contains a Black 2-Pin Connector With Black/Red & Brown Wires
GS400	Near Throttle Body & Contains a Black 2-Pin Connector With Black/Red & Brown Wires
LS400	Near Throttle Body & Contains a Black 2-Pin Connector With Red/Blue & Brown Wires
SC300	Left Front Of Cylinder Head & Contains a Green 2-Pin Connector With Light Green & Brown Wires
SC400	Near Throttle Body & Contains a Green 2-Pin Connector With Light Green & Brown Wires

Fig 1: Testing Engine Coolant Temperature (ECT) Sensor

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Engine Coolant Temperature (ECT) Sensor