This procedure covers removal and replacement of the coolant temperature sensor (ECT sensor) on the 2014-2019 Toyota Corolla 1.8L engine, including partial coolant drain and system refill.

Warnings

Tools required

Parts

• Coolant temperature sensor (ECT sensor) × 1 — Use OEM specification
• Coolant temperature sensor O-ring or gasket × 1 — Usually included with sensor

Fluids

• Toyota Super Long Life Coolant (Pink) — 1.5 qt

Preparation

1. Ensure engine is completely cold to the touch
2. Park vehicle on level surface and engage parking brake
3. Locate the coolant temperature sensor on the engine block near the thermostat housing on the driver's side of the engine
4. Place drain pan under the radiator drain plug or petcock area

Procedure

1. 1

   Disconnect the battery negative terminal
   Using a 10mm wrench, loosen and remove the negative battery cable from the battery terminal. Secure the cable away from the battery to prevent accidental reconnection.
2. 2

   Partially drain the cooling system
   Open the radiator drain plug or petcock at the bottom of the radiator. Drain approximately 1-2 quarts of coolant into the drain pan until the coolant level is below the ECT sensor location. Close the drain plug hand-tight once sufficient coolant has drained.
   Torque spec

   Drain Petcock6 Nm (5 lb-ft)
3. 3

   Disconnect the ECT sensor electrical connector
   Locate the electrical connector on the coolant temperature sensor. Press the locking tab and carefully pull the connector straight off the sensor. Do not pull on the wires themselves.
4. 4

   Remove the coolant temperature sensor
   Using a 19mm deep socket and ratchet, carefully loosen the ECT sensor by turning counterclockwise. Once loose, unscrew it by hand and remove it from the engine block. Some residual coolant may drain out; have shop towels ready to catch drips.
   ⚠If the sensor is difficult to remove, do not force it. Apply penetrating oil and allow to soak for 10-15 minutes before attempting again.
5. 5

   Clean the sensor mounting area
   Inspect the threaded hole in the engine block for debris or old gasket material. Use a wire brush or clean rag to clean the threads and mounting surface. Ensure no debris falls into the cooling system.
6. 6

   Install the new coolant temperature sensor
   Verify the new sensor has a fresh O-ring or gasket installed. Thread the new sensor into the engine block by hand, turning clockwise until finger-tight. Using the 19mm socket, snug the sensor firmly but do not overtighten. The sensor should be seated with moderate torque only (typically 15-20 Nm if using a torque wrench, though not specified in torque database).
   ⚠The ECT sensor threads into aluminum. Overtightening can strip the threads or crack the sensor body. Tighten only until snug plus 1/8 turn.
7. 7

   Reconnect the electrical connector
   Push the electrical connector firmly onto the new ECT sensor until you hear or feel the locking tab click into place. Gently tug on the connector to verify it is secure.
8. 8

   Refill the cooling system
   Pour Toyota Super Long Life Coolant (Pink) into the radiator or coolant reservoir until the level reaches the appropriate mark. Start with approximately 1-2 quarts to replace what was drained. Add coolant slowly to allow air to escape.
9. 9

   Bleed air from the cooling system
   With the radiator cap off, start the engine and allow it to idle. Turn the heater to maximum heat. Watch the coolant level and add coolant as needed while the engine warms up and the thermostat opens. Continue until no air bubbles emerge and the coolant level stabilizes. Allow engine to reach normal operating temperature.
   ⚠Monitor engine temperature gauge during bleeding process. If temperature approaches the red zone, shut off engine immediately and allow to cool.
10. 10

    Check for leaks and reconnect battery
    With the engine at operating temperature, inspect the ECT sensor for any coolant leaks around the base. Turn off the engine and allow to cool slightly. Top off coolant to the FULL mark as needed, then install the radiator cap. Reconnect the negative battery terminal and tighten securely.

Reassembly

1. Ensure all electrical connections are fully seated and locked
2. Verify the radiator drain plug or petcock is properly tightened to prevent leaks
3. Confirm coolant level is at the FULL mark on the reservoir when cold

Verification

• Start the engine and verify it reaches normal operating temperature without overheating
• Check that the temperature gauge on the instrument cluster operates normally
• Use an OBD-II scanner to verify no ECT sensor-related trouble codes are present
• Inspect the sensor installation point for any coolant leaks after the engine has fully warmed up
• Verify the engine cooling fan cycles on and off properly as the engine reaches operating temperature

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