AutoCodes – Subaru – P0128 Subaru

P0128 Subaru Code - Coolant Thermostat Malfunction

Quick Answer

Indicates that the thermostat monitor has not achieved the required engine operating temperature within a specified amount of time after starting the engine. 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 Subaru indicates Coolant Thermostat Malfunction.
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 29,804

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jun 14, 2020

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0128 Subaru Description

Indicates that the thermostat monitor has not achieved the required engine operating temperature within a specified amount of time after starting the engine.

OBDII Code P0128 Subaru - Coolant Thermostat Malfunction - AutoCodes.com — P0128 Subaru Code - Coolant Thermostat Malfunction

What does this mean?

What are the Possible Causes of the DTC P0128 Subaru?

Leaking or stuck open thermostat
Low engine coolant level
Insufficient warm up time
Faulty engine coolant temperature sensor
Engine coolant temperature sensor harness is open or shorted
Engine coolant temperature sensor circuit poor electrical connection

How to Fix the DTC P0128 Subaru?

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

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0128 Subaru 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.

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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 Subaru Code

1. What are the common symptoms of OBDII code P0128 - Coolant Thermostat Malfunction in a Subaru?

- Common symptoms may include the engine running colder than normal, decreased fuel efficiency, and the check engine light illuminating on the dashboard.

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

- The code P0128 in a Subaru is often caused by a faulty thermostat, low coolant levels, a malfunctioning coolant temperature sensor, or issues with the cooling system.

3. How serious is the Coolant Thermostat Malfunction code P0128 in a Subaru?

- While driving with a P0128 code may not immediately cause severe damage, it can lead to decreased engine performance, reduced fuel efficiency, and potential long-term damage if left unresolved.

4. Can I continue driving my Subaru with the OBDII code P0128?

- It is recommended to address the P0128 code promptly to prevent potential damage to the engine and to ensure optimal performance of your Subaru.

5. How can I diagnose the Coolant Thermostat Malfunction code P0128 in my Subaru?

- Diagnosis typically involves checking the coolant level, inspecting the thermostat, testing the coolant temperature sensor, and examining the overall condition of the cooling system.

6. What is the typical repair process for fixing the OBDII code P0128 in a Subaru?

- The repair process usually involves replacing the thermostat, addressing any coolant leaks, testing and potentially replacing the coolant temperature sensor, and ensuring the proper functioning of the cooling system.

7. Can I reset the check engine light after fixing the P0128 code in my Subaru?

- Yes, the check engine light can be reset using an OBDII scanner after fixing the underlying issue causing the P0128 code in your Subaru.

8. How much does it cost to repair the Coolant Thermostat Malfunction code P0128 in a Subaru?

- The cost of repairs for the P0128 code in a Subaru can vary depending on the specific issue, but it might range from $150 to $400, including parts and labor.

9. Are there any preventive measures to avoid the OBDII code P0128 in a Subaru?

- Regular maintenance, such as coolant system checks, thermostat inspections, and timely repairs of any cooling system issues, can help prevent the occurrence of the P0128 code in a Subaru.

10. Will fixing the Coolant Thermostat Malfunction code P0128 improve my Subaru's performance?

- Yes, addressing the P0128 code and ensuring proper cooling system function can improve engine performance, fuel efficiency, and overall reliability of your Subaru.