Fix P0128 Code: Coolant Thermostat – Causes & Symptoms

Have you ever been driving your car and suddenly noticed a flashing light on your dashboard? That light could be indicating a fault code, specifically the p0128 code. But what does it mean?

The p0128 code is a diagnostic trouble code that indicates an issue with the engine’s coolant temperature being too low. This can cause several problems, including decreased fuel efficiency and increased emissions.

Understanding trouble codes like the p0128 can seem daunting, but it’s essential for maintaining your vehicle’s health.

So buckle up and get ready to learn about one of the most common fault codes in modern vehicles: the p0128.

Symptoms of a P0128 code

What are the symptoms of the P0128 code?

The P0128 code is a common OBD-II trouble code that indicates that your engine is running too cold. This can cause several symptoms, including:

  • Check engine light on: The most common symptom of the P0128 code is the illumination of the check engine light on your dashboard. When this happens, it’s important to have your vehicle diagnosed by a professional mechanic.

  • Poor fuel economy: If your engine is running too cold, it can cause poor fuel economy. This means you’ll need to fill up more often than usual, which can be expensive over time.

  • Reduced engine power: In some cases, the P0128 code can cause reduced engine power. This means your vehicle may not accelerate as quickly as it should or may struggle to climb hills.

What are the common symptoms of the P0128 code?

While there are several symptoms associated with the P0128 code, some are more common than others. Here are a few additional symptoms you may experience:

  • The engine takes longer to warm up: If you notice that your engine takes longer than usual to warm up, it could be a sign that you have a problem with the thermostat or coolant system.

  • Temperature gauge reads lower than normal: If your temperature gauge reads lower than normal or doesn’t move at all, it could be an indication that there’s an issue with your cooling system.

  • Coolant leaks: Another symptom of the P0128 code is coolant leaks. If you notice puddles of coolant under your vehicle or see steam coming from under the hood, it’s important to have your car checked out right away.

What causes a P0128 code?

There are several potential causes for a P0128 code. Some of these include:

  • Faulty thermostat: The most common cause of a P0128 code is a faulty thermostat. If your thermostat is stuck open, it can cause your engine to run too cool.

  • Low coolant levels: If your coolant levels are low, it can cause your engine to run too cool. This could be due to a leak in the system or simply because you haven’t topped off the coolant recently.

  • Faulty coolant temperature sensor: The coolant temperature sensor is responsible for sending information about the engine’s temperature to the computer. If this sensor is faulty, it can cause the P0128 code to appear.

  • Faulty intake air temperature sensor: In some cases, a faulty intake air temperature sensor can cause the P0128 code. This sensor measures the temperature of incoming air and sends that information to the computer.

Also Read: P0507 Code: Causes, Symptoms, and Fixes

How to Diagnose a P0128 Code Using FIXD

P0128 Codes

FIXD: The Quick and Accurate Solution

If you’re experiencing a P0128 code, you don’t need to panic. With the help of FIXD, diagnosing and fixing the issue is quick and easy. FIXD is an innovative diagnostic tool that helps car owners identify problems in their vehicles without needing to visit a mechanic. It’s an affordable solution that can save you time and money in the long run.

Fixing P0128 Issues Yourself with FIXD

One of the best things about using FIXD is that it empowers car owners to fix issues themselves. When your vehicle’s engine light comes on, it can be daunting to try and determine what’s wrong. However, with FIXD, you’ll receive clear explanations of what’s causing the problem, along with step-by-step instructions on how to fix it.

The P0128 code indicates that there is an issue with your vehicle’s coolant temperature system. This could be due to a faulty thermostat or other mechanical issues related to the cooling system. With FIXD, you’ll receive real-time data about your vehicle’s temperature levels and alerts if they rise beyond safe levels.

FIXD also provides helpful resources for DIY repairs, including video tutorials and guides on how to replace components like thermostats or sensors. By using these resources alongside your diagnostic results from FIXD, you’ll be able to confidently make repairs yourself without needing professional assistance.

Preventing Future P0128 Codes with Real-Time Data

Another great feature of FIXD is its ability to provide real-time data about your vehicle’s performance. This includes monitoring temperature levels and alerting you if they exceed safe ranges. By keeping an eye on these metrics regularly, you can prevent future occurrences of the P0128 code from appearing.

FIXD tracks maintenance schedules for your vehicle and alerts you when it’s time for routine upkeep. This includes oil changes, tire rotations, and other important tasks that can help keep your car running smoothly. By following these schedules, you’ll be able to maintain your vehicle’s health and prevent issues like the P0128 code from appearing in the first place.

Checking Coolant and Inspecting the Coolant Temperature Sensor for a P0128 Code

Check the Coolant Level Before Inspecting the Coolant Temperature Sensor for a P0128 Code

The P0128 code is related to the engine’s coolant temperature, which means that it could be caused by various issues within the coolant system. However, before inspecting any components of the coolant system, it’s essential to check the coolant level first. A low coolant level could cause the engine to overheat, which would trigger a P0128 code.

To check the coolant level, locate your vehicle’s radiator cap and remove it when your engine is cool. Look inside and ensure that there is enough coolant in the radiator. If you can’t see any fluid or if it’s below the recommended level, add more until it reaches its proper capacity.

A Faulty Thermostat Can Cause The Engine Coolant Temperature to Remain Below the Regulating Temperature, Triggering a P0128 Code

One common reason for a P0128 code is a faulty thermostat. The thermostat regulates your engine’s temperature by allowing or blocking off coolant flow through your engine block. When your engine starts up cold, your thermostat stays closed to allow it to warm up quickly. Once it reaches its operating temperature range, your thermostat opens up and allows hot coolant to circulate throughout your cooling system.

If your thermostat gets stuck in an open position or fails entirely (stuck closed), this can cause problems with regulating engine temperature properly. When this happens, there may not be enough heat generated within your engine block causing it to stay below its regulating temperature range triggering a P0128 code.

Inspect the Radiator Hose, Radiator, and Heater For Any Leaks or Damages That May Affect The Engine Coolant Temperature

When diagnosing a P0128 code issue on vehicles with high mileage or older age models; inspecting other components of the coolant system is crucial. Over time, components such as radiator hoses, radiators, and heaters can become brittle, crack or develop leaks that will affect your engine’s coolant temperature.

Inspecting these components for any damages is essential to ensure that they are functioning correctly. Look for signs of wear or damage such as cracks, bulges, or leaks in the hoses and radiator. If you find any issues with these components, replace them immediately to avoid further damage to your engine.

DIY Steps to Diagnose and Fix a P0128 Code

Fix P0128 Code

Check the Coolant Level and Condition

The first step in diagnosing a P0128 code is to check the coolant level and condition. Low coolant levels or poor-quality coolant can cause the engine to overheat, which triggers the code. If you notice that the coolant level is low, top it up with the recommended type of coolant for your vehicle. Check if there are any leaks in the cooling system, such as hoses or radiators, which could also cause low coolant levels.

Use an OBD-II Scanner to Retrieve Freeze Frame Data

An OBD-II scanner is a tool used by mechanics and car owners to diagnose issues with a vehicle’s electronic systems. When a P0128 code appears on your dashboard, use an OBD-II scanner to retrieve freeze frame data from your car’s computer system. This data will provide information about what was happening when the code was triggered, such as engine speed, throttle position, and fuel trim.

Once you have this information, you can identify the specific cause of the code. For example, if you notice that the engine temperature was too high when the code appeared, it could be due to a malfunctioning thermostat or faulty temperature sensor.

Inspect the Thermostat for Proper Operation

If your OBD-II scan reveals that there may be an issue with your thermostat’s operation or if you suspect it is not working correctly based on other symptoms (e.g., slow warm-up time), inspect it thoroughly. The thermostat regulates engine temperature by opening and closing depending on whether cold or hot water needs to flow through it.

To test whether your thermostat is working correctly:

  1. Remove it from its housing.

  2. Place it in boiling water for 10 minutes.

  3. Use tongs to remove it from boiling water carefully.

  4. Observe whether it opens fully after being removed from boiling water.

If the thermostat does not open fully, it is faulty and needs to be replaced. A malfunctioning thermostat can cause the engine to overheat, which leads to a P0128 code.

Check the Engine’s Coolant Temperature Sensor

The coolant temperature sensor monitors engine temperature and sends signals to the car’s computer system. If there are any issues or faults with this sensor, it can cause a P0128 code to appear on your dashboard. To check whether the sensor is working correctly:

  1. Locate the coolant temperature sensor in your vehicle’s engine bay.

  2. Disconnect its electrical connector.

  3. Use a multimeter tool to measure its resistance.

  4. Compare your readings with manufacturer specifications.

If you notice any discrepancies between your readings and manufacturer specifications, replace the coolant temperature sensor.

Clear the Code and Test Drive Your Vehicle

Once you have identified and fixed any issues that caused a P0128 code in your vehicle, clear the code using an OBD-II scanner or disconnect your battery for 10-15 minutes before reconnecting it. After clearing the code, test drive your vehicle for at least 20 minutes under normal driving conditions.

During this test drive, pay attention to how quickly your engine warms up and whether there are any unusual noises or vibrations coming from underneath your hood. If everything seems normal after completing these steps, then congratulations! You have successfully diagnosed and fixed a P0128 code in your vehicle.

Tips from a Mechanic on Diagnosing and Fixing a P0128 Code

What is a P0128 Code?

A P0128 code is a diagnostic trouble code (DTC) that indicates that the engine coolant temperature (ECT) sensor has detected a lower-than-normal temperature reading for the engine. This can happen when the thermostat isn’t working correctly, or there’s an issue with the ECT sensor itself.

How Does a Mechanic Diagnose the P0128 Code?

To diagnose a P0128 code, a mechanic will typically use an OBD II scanner to retrieve the code from the car’s engine control module. The scanner will provide information on what caused the code to trigger, such as whether it was due to an issue with the thermostat or ECT sensor.

Once the cause of the problem has been identified, the mechanic will need to perform further testing to determine exactly what needs to be fixed. This may involve checking wiring connections, testing components like thermostats and sensors, and inspecting other parts of the engine for damage or wear.

How to Fix Trouble Code P0128

Fixing a P0128 code often involves replacing either the thermostat or ECT sensor. In some cases, both components may need to be replaced if they are found to be faulty.

Before replacing any parts, however, it’s important to ensure that they are actually causing the problem. Sometimes issues with wiring connections or other parts of the engine can cause false readings from sensors like those used in detecting coolant temperature.

If you’re not comfortable diagnosing and fixing this issue yourself, it’s best to take your car to an experienced mechanic who can properly diagnose and repair any problems.

What Kind of OBD II Scanner is Needed to Diagnose P0128 Code?

Any good quality OBD II scanner should be able to retrieve codes like P0128 from your car’s engine control module. However, it’s important to ensure that the scanner you choose is compatible with your car’s make and model.

Some scanners are designed specifically for certain types of vehicles or engines, so it’s important to do your research and find one that will work with your car.

In addition to being able to retrieve codes, a good OBD II scanner should also provide detailed information on what caused the code to trigger. This can help you diagnose and fix the problem more quickly and efficiently.

Possible Repair Costs for a P0128 Code

What Repairs Can Fix the P0128 Code?

A P0128 code is a common issue among car owners, and it usually indicates that there is a problem with the engine coolant temperature (ECT) sensor or thermostat. To fix this issue, you need to replace either of these parts in your car.

The ECT sensor is responsible for sending signals to your car’s computer about the temperature of the engine coolant. If it fails to do so, your car’s computer may assume that the engine is running cold and trigger the P0128 code. The cost of replacing an ECT sensor ranges from $50 to $200, depending on the make and model of your car.

On the other hand, if your thermostat is stuck open or malfunctioning, it may cause the engine coolant to circulate continuously, leading to low operating temperatures. This can also trigger a P0128 code. Replacing a thermostat costs around $100 to $300, depending on where you live and what type of vehicle you own.

How Much Does It Cost to Fix the P0128 Issue?

The cost of fixing a P0128 issue depends on several factors such as:

  • The severity of the problem

  • The make and model of your vehicle

  • Your location

If you catch this issue early on when it first appears, then it may not cost much to repair. However, if you ignore it for too long or if there are underlying issues causing this error code, then repairs could be more expensive.

Typically, repairing a P0128 code can range from $100 up to $500 or more in some cases. Therefore, it’s essential that you take care of this problem as soon as possible before further damage occurs.

Who Has The Lowest Price?

When looking for repair options for your P0128 code issue, several factors come into play, such as your location, the make and model of your vehicle, and the severity of the problem. Therefore, it’s difficult to determine who has the lowest price without considering these factors.

However, you can use online repair cost calculators to get an idea of how much repairs may cost in your area. You can shop around for quotes from different mechanics to see who offers the best price for repairing your P0128 code issue.

Understanding and Resolving a P0128 Code Issue

If you’re experiencing issues with your car’s engine, one possible culprit could be the P0128 code. This code indicates that your engine is not warming up properly, which can lead to decreased performance and potential damage over time. Here are some key points to keep in mind when dealing with a P0128 code:

Symptoms of a P0128 Code

The symptoms of a P0128 code can include reduced engine performance, decreased fuel efficiency, and a noticeable drop in power output. You may also notice that your car takes longer than usual to warm up or that it struggles to maintain its temperature while driving.

How to Diagnose a P0128 Code using FIXD

One tool that can help diagnose a P0128 code is FIXD, an app that connects to your car’s OBD-II port and provides real-time diagnostic information. By using this app, you can get detailed insights into what might be causing the issue and take steps to resolve it.

Checking Coolant and Inspecting the Coolant Temperature Sensor for a P0128 Code

Another way to diagnose a P0128 code is by checking your coolant levels and inspecting the coolant temperature sensor. If your coolant levels are low or if there’s an issue with the sensor itself, this could be causing the problem.

DIY Steps to Diagnose and Fix a P0128 Code

If you’re comfortable working on cars yourself, there are several steps you can take to diagnose and fix a P0128 code. These include checking your thermostat, replacing your coolant temperature sensor, or flushing out your radiator.

Tips from a Mechanic on Diagnosing and Fixing a P0128 Code

If you’re not sure where to start may be helpful to consult with an experienced mechanic. They can provide you with expert advice and help you troubleshoot the issue more effectively.

Possible Repair Costs for a P0128 Code

The cost of repairing a P0128 code will depend on several factors, including the severity of the issue and the type of repairs needed. In general, however, you can expect to pay anywhere from $100 to $500 for parts and labor.

In conclusion, dealing with a P0128 code can be frustrating, but there are steps you can take to diagnose and fix the issue. By staying informed about the symptoms of this code and using tools like FIXD or consulting with a mechanic as needed, you can keep your car running smoothly and avoid costly damage over time.


What causes a P0128 code?

A P0128 code is typically caused by issues with your engine’s cooling system, such as low coolant levels or a malfunctioning thermostat.

Can I still drive my car with a P0128 code?

While it’s technically possible to drive your car with a P0128 code, doing so could lead to decreased performance and potential damage over time. It’s best to get the issue resolved as soon as possible.

Is it safe to replace my own coolant temperature sensor?

If you have experience working on cars and feel comfortable doing so, then replacing your own coolant temperature sensor may be an option. However, if you’re not sure what you’re doing or don’t have experience in this area, it’s best to consult with an experienced mechanic instead.

How long does it take to fix a P0128 code?

The length of time it takes to fix a P0128 code will depend on several factors, including the severity of the issue and the type of repairs needed. In some cases, fixing this problem may only take an hour or two; in other cases, it may require more extensive repairs that could take several days.

Will a P0128 code go away on its own?

No, a P0128 code will not typically go away on its own. It’s important to diagnose and resolve the issue as soon as possible to prevent further damage to your engine.

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