Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSTOYOTA2001HIGHLANDER 2WD L4-2.4L (2AZ-FE)REPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSSENSORS AND SWITCHES - COMPUTERS AND CONTROL SYSTEMSCOOLANT TEMPERATURE SENSOR/SWITCH (FOR COMPUTER)DESCRIPTION AND OPERATION
2001 Toyota Highlander 2WD L4-2.4L (2AZ-FE)
Coolant Temperature Sensor/Switch (For Computer): Description and Operation
2001 Toyota Highlander 2WD L4-2.4L (2AZ-FE)SECTION Description and Operation
Engine Coolant Temperature Sensor
A thermistor that is built into the engine coolant temperature sensor changes the resistance value according to the engine coolant temperature.
The lower the engine coolant temperature sensor, the greater the thermistor resistance value, and the higher the engine coolant temperature sensor temperature, the lower the thermistor resistance value.
The engine coolant temperature sensor is connected to the ECM. The 5 V power source voltage in the ECM is applied to the engine coolant temperature sensor from the terminal THA via a resistor R. That is, the resistor R and the engine coolant temperature sensor are connected in series.
When the resistance value of the engine coolant temperature sensor changes in accordance with changes in the engine coolant temperature, the potential at terminal THA also changes. Based on this signal, the ECM increases the fuel injection volume to improve driveability during cold engine operation.
A thermistor that is built into the engine coolant temperature sensor changes the resistance value according to the engine coolant temperature.
The lower the engine coolant temperature sensor, the greater the thermistor resistance value, and the higher the engine coolant temperature sensor temperature, the lower the thermistor resistance value.
The engine coolant temperature sensor is connected to the ECM. The 5 V power source voltage in the ECM is applied to the engine coolant temperature sensor from the terminal THA via a resistor R. That is, the resistor R and the engine coolant temperature sensor are connected in series.
When the resistance value of the engine coolant temperature sensor changes in accordance with changes in the engine coolant temperature, the potential at terminal THA also changes. Based on this signal, the ECM increases the fuel injection volume to improve driveability during cold engine operation.
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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.