How to Replace the Coolant Sensor in a Toyota 4Runner

by Dan Ferrell
Photo courtesy of IFCAR at

The Engine Coolant Temperature (ECT) sensor has a direct impact on your Toyota-4Runner engine performance. On newer models, the computer controlled spark advance system uses information from the ECT and other sensors to adjust ignition timing to engine operating conditions at any given time. Therefore, a malfunctioning ECT sensor will have an effect on engine operation. If you have detected a bad coolant temperature sensor, replacing it with a new unit will solve the problem.

Removing the ECT Sensor

Step 1

Place a catch pan under the radiator. Remove the radiator cap, and open the radiator drain valve. Remove at least 2 quarts of coolant. Then close the radiator drain valve, and replace the radiator cap.

Step 2

Disconnect the upper radiator hose from the water housing at the engine side. Use a standard screwdriver or a pair of rib joint pliers, depending on the type of clamp used on your particular model.

Step 3

Detach the upper radiator hose from the water housing.

Step 4

Remove the upper timing belt cover using a ratchet and socket to gain access to the coolant temperature sensor near the water housing, if necessary.

Step 5

Remove the fuel pipe on top of the engine as well to gain access to the ECT sensor, if necessary. Use a tube wrench to remove the two union bolts at each side of the pipe. Discard the fuel pipe 4 gaskets.

Step 6

Unplug the electrical connector from the coolant temperature sensor by pressing the lock tab and pulling the plastic connector from the sensor's fitting. See the resources box for more information.

Unscrew the coolant temperature sensor from the engine using a wrench or ratchet, ratchet extension and deep socket.

Installing the ECT Sensor

Step 1

Screw the coolant temperature sensor in place with your hand, along with a new gasket to avoid damage to the threads. Then tighten the sensor, using the wrench or ratchet, ratchet extension and socket.

Step 2

Plug the sensor electrical connector.

Step 3

Install the fuel pipe, along with 4 new gaskets, and tighten the union bolts, using the tube wrench, if you had to disconnect it.

Step 4

Attach the upper timing belt cover using the ratchet and socket, if you had to remove it.

Step 5

Connect the upper radiator hose to the water housing, and tighten the hose clamp, using the standard screwdriver or rib joint pliers.

Refill the coolant system with 50 percent water and 50 percent new anti-freeze.


  • Your Toyota 4Runner service manual will help you locate and identify components, if necessary. Buy one at most auto parts stores, or check one at your local public library.


  • Store and dispose of used coolant properly. The antifreeze may attract cats, dogs and even young kids with fatal results. Make sure the coolant temperature is low before starting to replace the ECT sensor. Removing the radiator cap on a hot engine may blow coolant out, and cause severe skin burns, and other serious injuries.

Items you will need

  • Catch pan
  • Standard screwdriver or rib joint pliers
  • Ratchet and deep socket
  • Tube wrench
  • Wrench
  • Ratchet extension
  • 4 new fuel pipe gaskets
  • New anti-freeze

More Articles