Engine-CodesMitsubishi – P0128 Mitsubishi

P0128 Mitsubishi Code - Coolant Thermostat Malfunction

Quick Answer

The P0128 code in a Mitsubishi indicates a malfunction in the coolant thermostat. Common causes include Thermostat stuck in the open position, Faulty coolant temperature sensor, Low coolant level. 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 Mitsubishi indicates Coolant Thermostat Malfunction.
Common causes
Common causes include Thermostat stuck in the open position, Faulty coolant temperature sensor, Low coolant level.
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.
Table of contents Created and updated by William Orellana on Sep 12, 2024
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Code P0128 Mitsubishi Description

The P0128 code in a Mitsubishi indicates a malfunction in the coolant thermostat. The coolant thermostat is a crucial component of the vehicle's cooling system, responsible for regulating the flow of coolant through the engine to maintain optimal operating temperature. When the thermostat fails to function properly, it can lead to serious issues with the engine's performance and overall health.

OBDII Code P0128 Mitsubishi - Coolant Thermostat Malfunction
P0128 Mitsubishi Code - Coolant Thermostat Malfunction

Common Causes of P0128 Mitsubishi

  1. Thermostat stuck in the open position
  2. Faulty coolant temperature sensor
  3. Low coolant level
  4. Air pockets in the cooling system
  5. Electrical issues with the thermostat circuit

Symptoms of P0128 Mitsubishi

  1. Engine running colder than normal
  2. Decreased fuel efficiency
  3. Check Engine Light illuminated
  4. Poor heater performance
  5. Overheating in extreme cases

How to Fix P0128 Mitsubishi

  1. Begin by diagnosing the issue using a scan tool to confirm the P0128 code and check the coolant temperature sensor's readings.
  2. Inspect the thermostat for proper operation and replace it if found to be faulty.
  3. Check the coolant level and bleed the cooling system to remove any air pockets.
  4. Test the thermostat's electrical circuit for any faults and repair as necessary.
  5. Clear the trouble code and test drive the vehicle to ensure the issue has been resolved.

Cost to Fix P0128 Mitsubishi

The cost of repairing a coolant thermostat malfunction in a Mitsubishi can vary depending on the specific model and year of the vehicle. On average, the parts for this repair can range from $50 to $200, while labor costs can range from $100 to $300. Overall, the total cost of addressing this issue typically falls between $150 and $500. It's important to note that these are rough estimates, and actual costs may vary based on various factors such as location, labor rates, and additional repairs needed. It is recommended to consult with a qualified mechanic or auto repair shop for a more accurate cost estimate.

Tech Notes for P0128 Mitsubishi

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

When is the Code Detected?

The engine coolant temperature does not reach to specified temperature even though the engine has run long enough.

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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 Mitsubishi Code

1. What does the OBDII code P0128 mean on a Mitsubishi?

P0128 indicates that the engine’s coolant temperature is not reaching the expected threshold in a timely manner, often due to a thermostat malfunction.

2. What are the common symptoms of code P0128?

Symptoms include an illuminated check engine light, poor fuel efficiency, lower engine temperature readings, and reduced cabin heater performance.

3. What causes code P0128 on a Mitsubishi?

Common causes include a stuck-open thermostat, low coolant levels, a faulty coolant temperature sensor, or issues with the cooling system.

4. Can I drive my Mitsubishi with a P0128 code?

While it’s possible to drive, prolonged use can lead to poor fuel economy and increased engine wear due to improper operating temperatures.

5. How do I fix a P0128 code on a Mitsubishi?

Repairs may involve replacing the thermostat, refilling coolant, checking for leaks, or replacing the coolant temperature sensor.

6. How much does it cost to fix a P0128 code?

The cost varies, but replacing a thermostat typically costs $150-$300, including parts and labor, depending on the model.

7. Will clearing the P0128 code fix the problem?

Clearing the code doesn’t resolve the underlying issue; you must identify and repair the cause to prevent the code from returning.

8. Can a P0128 code affect fuel economy?

Yes, an engine running cooler than designed can cause inefficient combustion, leading to lower fuel efficiency.

9. How can I diagnose a P0128 code on a Mitsubishi?

Diagnose by checking coolant levels, inspecting the thermostat, testing the coolant temperature sensor, and ensuring the cooling system is functioning properly.

10. What happens if I ignore a P0128 code?

Ignoring the code can lead to reduced engine performance, higher fuel consumption, and potential long-term damage due to improper engine temperatures.

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