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AutoCodes – Toyota – P0128 Toyota

P0128 Toyota Code - Coolant Thermostat

Quick Answer

The ECM estimates the engine coolant temperature based on the starting temperature, engine loads, and engine speeds. Common causes include Leaking or stuck open thermostat, Low engine coolant level, Insufficient warm up time. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
P0128 Toyota indicates Coolant Thermostat.
Common causes
Common causes include Leaking or stuck open thermostat, Low engine coolant level, Insufficient warm up time.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
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Code Popularity 90,549
How popular is this code, among other codes? Medium
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Table of contents Created and updated by William Orellana on Aug 23, 2022
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Code P0128 Toyota Description

The ECM estimates the engine coolant temperature based on the starting temperature, engine loads, and engine speeds. The Engine Control Module (ECM) then compares the estimated temperature with the actual engine coolant temperature. When the estimated engine coolant temperature reaches 75°C (167°F), the ECM checks the actual engine coolant temperature. If the actual engine coolant temperature is less than 75°C (167°F), the ECM interprets this as a malfunction in the thermostat or the engine cooling system and stores the Diagnostic Trouble Code (DTC).
OBDII Code P0128 Toyota - Coolant Thermostat - AutoCodes.com
P0128 Toyota Code - Coolant Thermostat
What does this mean?

What are the Possible Causes of the DTC P0128 Toyota?

  • Leaking or stuck open thermostat
  • Low engine coolant level
  • Insufficient warm up time
  • Faulty Engine Coolant Temperature (ECT) sensor
  • Engine Coolant Temperature sensor harness is open or shorted
  • Engine Coolant Temperature sensor electrical circuit poor connection
  • Faulty Engine Control Module (ECM)

How to Fix the DTC P0128 Toyota?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What does this mean?

Code Tech Notes

If the cooling system is not leaking and the fluid level is OK, replacing the thermostat usually takes care of the problem.





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What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0128 Toyota code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P0128 Toyota code?

Need more information on how to fix the P0128 Toyota code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0128 Toyota code diagnosed by a professional: Find a repair shop in your area

Information for Specific Toyota Models

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0128 Toyota Code

1. What are the common symptoms of OBDII code P0128 in a Toyota related to the coolant thermostat?

- The common symptoms include the engine running cooler than normal, a decrease in fuel efficiency, and the check engine light coming on.

2. What are the possible causes of the P0128 code in a Toyota?

- The code P0128 is often triggered by a faulty thermostat, low coolant levels, a malfunctioning coolant temperature sensor, or a stuck open thermostat.

3. How can I diagnose the P0128 code in my Toyota related to the coolant thermostat?

- Diagnosis typically involves checking the coolant level, inspecting the thermostat for proper operation, testing the coolant temperature sensor, and ensuring there are no leaks in the cooling system.

4. Can I drive my Toyota with the P0128 code related to the coolant thermostat?

- It is not recommended to drive your Toyota with the P0128 code, as it can lead to engine damage and reduced performance. It is best to address the issue promptly.

5. What is the repair procedure for the P0128 code in a Toyota?

- The repair usually involves replacing the thermostat, topping up the coolant, resetting the fault codes, and verifying that the issue has been resolved.

6. How long does it take to repair the P0128 code related to the coolant thermostat in a Toyota?

- The repair time can vary depending on the exact cause of the issue, but replacing the thermostat and performing necessary checks typically takes around 1-2 hours.

7. Are there any preventive maintenance tips to avoid the P0128 code in a Toyota?

- Regularly checking and maintaining the coolant level, flushing the cooling system as recommended, and replacing the thermostat at the recommended intervals can help prevent the P0128 code.

8. Can a DIY enthusiast fix the P0128 code related to the coolant thermostat in a Toyota?

- If you have the necessary tools and experience, you may be able to replace the thermostat yourself. However, it is recommended to consult a professional mechanic for an accurate diagnosis and repair.

9. Will resetting the check engine light resolve the P0128 code in a Toyota?

- Simply resetting the check engine light will not fix the underlying issue causing the P0128 code. It is important to diagnose the problem, make necessary repairs, and then reset the fault codes.

10. How much does it cost to repair the P0128 code related to the coolant thermostat in a Toyota?

- The cost of repairs can vary depending on the exact cause of the issue, but replacing the thermostat and addressing related components typically ranges from $150 to $400 at a repair shop.

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