FAULTBASE
Error CodesASKCars
© 2026 FAULTBASE
All rights reserved.
v2.0.0 • Production
ContactPrivacyImpressum
What are the typical signs of a failing thermostat in a 2022 Toyota Highlander? - Toyota Highlander
Home/Cars/Toyota/Highlander/Fourth Generation (2020-present)/What are the typical signs of a failing thermostat in a 2022 Toyota Highlander?

What are the typical signs of a failing thermostat in a 2022 Toyota Highlander?

Toyota Highlander Fourth Generation (2020-present)

Error Codes
2-3 hours
Time
medium
Difficulty
medium
Severity
Error Code: P0128
Navigation
ProblemSymptomsDiagnosisSolution
ProblemSymptomsDiagnosisSolution
4 min read
791 words

Problem Statement

Learn how to identify the signs of a failing thermostat in your 2022 Toyota Highlander and follow step-by-step instructions for diagnosis and repair.

Error Code
P0128
Affected Component
Thermostat
Estimated Time
2-3 hours

Symptoms

  • •Overheating Engine
  • •Poor Heater Performance
  • •Check Engine Light
  • •Coolant Leaks
  • •Inconsistent Temperature Gauge Readings

Diagnostic Steps

  1. 1
  2. 2
  3. 3
  4. 4
  5. 5

Solution

💡 Expert Tip

For complex repairs like this, consider taking photos at each step. This helps if you need to reverse a step or consult with a mechanic. Also, keep all removed parts organized - you may need to reference them during reassembly.

Verification

After completing the repair, verify that the issue has been resolved:

  • ✓Test the affected component to ensure it functions correctly
  • ✓Check for any error codes or warning lights
  • ✓Monitor the vehicle for a few days to ensure the issue does not recur

Prevention Tips

To prevent this issue from occurring again:

  • •Follow the manufacturer's recommended maintenance schedule
  • •Address warning signs early before they develop into major issues
  • •Use quality parts and fluids recommended for your vehicle
  • •Keep detailed records of all repairs and maintenance

Tools & Equipment Required

  • •Flashlight
  • •OBD-II scanner
  • •Cooling system pressure tester
  • •Infrared thermometer
  • •Coolant drain pan
  • •Socket set
  • •Wrench set
  • •Torque wrench
  • •Gasket scraper

Additional Information

Error Code
P0128
Affected Component
Thermostat
Estimated Time
2-3 hours
Difficulty
medium
Severity
medium
Tools Required
9 items

Related Faults

Loading...

Share this solution

Comments

Sign in to share your thoughts

Sign In

No comments yet

Be the first to share your thoughts

Back to Generation
Signs of a Failing Thermostat in a 2022 Toyota Highlander

When the thermostat in a vehicle begins to fail, it can cause a variety of symptoms that can affect the engine's performance and overall comfort of the vehicle. Here are typical signs to look out for in a 2022 Toyota Highlander:

1. Overheating Engine
  • Symptom: The temperature gauge on the dashboard rises above the normal operating range (usually around the middle of the gauge).
  • Cause: A stuck thermostat can prevent coolant from circulating properly, leading to overheating.
2. Poor Heater Performance
  • Symptom: The cabin heater blows cold air or fluctuates between hot and cold.
  • Cause: If the thermostat is stuck open, the engine may not reach the optimal operating temperature, which affects heater performance.
3. Check Engine Light
  • Symptom: The Check Engine Light (CEL) may illuminate.
  • Cause: Faulty thermostat readings can trigger an error code related to engine temperature.
4. Coolant Leaks
  • Symptom: Puddles of coolant under the vehicle or visible coolant on the engine.
  • Cause: A failing thermostat can lead to increased pressure in the cooling system, causing hoses to burst or gaskets to fail.
5. Inconsistent Temperature Gauge Readings
  • Symptom: Fluctuation in the temperature gauge readings while driving.
  • Cause: If the thermostat opens and closes erratically, it can cause the gauge to read inconsistently.
Step 1: Visual Inspection
  • Tools Required: Flashlight, gloves.
  • Instructions:
    • Inspect the thermostat housing for any signs of coolant leaks.
    • Check the coolant level in the reservoir and radiator.
Step 2: Monitor Temperature Gauge
  • Tools Required: None.
  • Instructions:
    • Start the engine and let it idle.
    • Observe the temperature gauge. It should gradually rise to the normal operating range and maintain that level.
Step 3: Check for Fault Codes
  • Tools Required: OBD-II scanner.
  • Instructions:
    • Connect the OBD-II scanner to the vehicle's diagnostic port.
    • Retrieve any error codes that could indicate thermostat issues (e.g., P0128 - Coolant Thermostat Range/Performance Problem).
Step 4: Cooling System Pressure Test
  • Tools Required: Cooling system pressure tester.
  • Instructions:
    • Attach the pressure tester to the radiator cap opening.
    • Pump the tester to apply pressure and observe if there are any leaks or if the pressure holds steady.
Step 5: Thermostat Function Test
  • Tools Required: Infrared thermometer, coolant drain pan, socket set.
  • Instructions:
    • Allow the engine to reach operating temperature while monitoring the temperature at the thermostat housing with an infrared thermometer.
    • If the engine is hot but the thermostat housing is cool, the thermostat may be stuck closed.
    • If the engine cools down too quickly after the thermostat opens, it may be stuck open.
Repair Instructions
Step 1: Gather Necessary Tools and Parts
  • Tools Required: Socket set, wrench set, coolant drain pan, torque wrench, gasket scraper, new thermostat, new gasket (if applicable), coolant.
Step 2: Allow Engine to Cool
  • Instructions:
    • Ensure the engine is cool to avoid burns.
Step 3: Drain Coolant
  • Instructions:
    • Place a drain pan under the radiator and open the drain valve to remove coolant.
Step 4: Remove Thermostat
  • Instructions:
    • Disconnect the negative battery terminal.
    • Remove any components obstructing access to the thermostat (e.g., air intake duct).
    • Locate the thermostat housing and remove the bolts using a socket set.
    • Carefully lift the housing away and remove the old thermostat.
Step 5: Install New Thermostat
  • Instructions:
    • Clean the mating surfaces on the engine and the thermostat housing to ensure a good seal.
    • Install the new thermostat in the housing, ensuring it's oriented correctly (check for a small jiggle valve if applicable).
    • Apply a new gasket or sealant as needed.
    • Reattach the thermostat housing and tighten the bolts to the manufacturer’s specified torque.
Step 6: Refill Coolant
  • Instructions:
    • Refill the cooling system with the appropriate coolant mixture.
    • Run the engine with the radiator cap off to allow air to escape until the thermostat opens and the coolant level stabilizes.
Step 7: Test Drive
  • Instructions:
    • After the repair, take the vehicle for a short drive.
    • Monitor the temperature gauge to ensure it stays within normal limits and check for any leaks.
Step 8: Recheck Coolant Level
  • Instructions:
    • After the engine cools down, recheck the coolant level and top off if necessary.

By following these steps, you can diagnose and repair a failing thermostat in a 2022 Toyota Highlander effectively. If symptoms persist after replacing the thermostat, further diagnostics may be needed to investigate other cooling system components.