P0128 Code (Meaning, Causes, Symptoms & Fixes)

When your check engine light is illuminated due to the P0128 code, you may have an issue with your engine thermostat. you should take these steps to fix the P0128 code. This article will help you to fix your thermostat and solve this problem code.

Many drivers ignore codes that lighten the Check Engine light but don’t have obvious symptoms. This strategy has a flaw.

Unless you have an active misfire (it flashes when it is severe enough), the MIL lights only know how to notify you of a problem; it doesn’t tell how many problems the ECM/PCM has found.

For example, let’s say you go to the parts shop or use your scanner. You get a P0128 engine Code and think you will take care of it later. But when “later” finally arrives, you find that you have five or six other problems besides the one that illuminated the check engine light.

The engine control module (ECM), which tracks the time it takes for a vehicle’s engine to reach the operating temperature, monitors this temperature.

The powertrain control module commands the fuel system to enter “closed-loop,” where oxygen sensor readings are used to maintain a 14.7:1 ratio.

ECMs require that the Engine coolant temperature sensor records temperatures beyond 160 F within 15 minutes after the engine starts.

The engine temperature recorded must not drop below 160 F after the threshold of 160 F has been reached. If any one of these criteria is not met, the PCM will report it to the PCM. Code P0128 will be triggered if either of these faults is again recorded on the next engine start.

Also Read: P0456 Code – Meaning, Causes, Symptoms & Fixes

What Causes The P0128 Code?

p0128 causes

Common causes of the P0128 code are:

  1. Faulty or sticky thermostat
  2. Coolant bypassing closed thermostats because the thermostat seal isn’t sealing properly
  3. Faulty engine coolant temperature (ECT) sensor
  4. The engine computer (PCM) software must be updated
  5. Low coolant level
  6. Radiator fan doesn’t turn off
  7. Faulty intake temperature (IAT sensor)

P0128 Code Symptoms?

These are the most common symptoms you will experience if your car is triggering the P0128 code.

  1. Check Engine Light is On
  2. Warm-up takes longer
  3. Driving on the highway causes the temperature of your engine to drop significantly.
  4. The temperature gauge indicates cooler than it usually does
  5. The heater won’t work optimally
  6. A P0128 will usually not be as noticeable due to a reduced fuel economy.
  7. Failed emissions test or monitors “not ready” for emissions testing.

How Serious Is The P0128 Code?

How Serious Is The P0128 Code
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P0128 is not considered a serious code. However, if not fixed and the car is used over a long time, there is a slight chance that water contamination of the oil could cause deterioration and engine damage. This code is set when the coolant doesn’t get hot enough.

It means that the engine is not heating up enough to burn off the condensation. That water could then end up in oil. Engine damage can occur over many years, although it is unlikely.

How To Diagnose And Repair Code P0128

  1. To verify that P0128 is the only code in your vehicle, scan it. Other codes must first be addressed.
  2. Make sure to check the coolant level. Excessive rust or poor coolant conditions can cause the cooling system to clog and the thermostat to stick. Flush the coolant system to ensure it is in good condition. Check for leaks if the coolant level drops.
  3.  A Multimeter is used to check the coolant temperature sensor. The temperature will affect the ohm reading. If the ohm reading does not change with temperature, replace the coolant temperature sensor.
  4. A stuck engine coolant thermostat most commonly causes a P0128 code. This can be easily diagnosed by feeling the radiator hose to determine how hot the coolant is as it flows through the radiator. It would be best if you were more careful, as you may burn yourself. The thermostat should open when the hose is barely warm. The thermostat should open when the coolant starts to flow, as this will quickly heat the radiator. If the radiator heats slowly, it is likely that the thermostat has been prematurely opened or stuck open.

How To Fix The P0128 code?

How To Fix The P0128 code
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The following repairs can fix the P0128 code

  1. Replacing the thermostat (most common repair)
  2. Replacing the coolant temperature sensor, or also replacing the wiring and connector associated with the sensor being damaged
  3. Coolant system leaking bleeding air
  4. Check the coolant temperature and test drive it
  5. Look for leaks

Watch this video guide on how to fix the P0128 engine code

How Much Does It Cost To Fix P0128 Code

P0128 code repair costs can be anywhere from $140 to $250. The estimated repair cost for each repair is inclusive of both the labor and parts costs. Thermostat $220-$250, a Temperature sensor for coolant $140-$190. These prices may vary depending on your care make and model and your location.

Also Read: P0700 Code (Meaning, Causes, Symptoms & Fixes)

Frequently Asked Questions

What can cause a P0128?

P0128 most often occurs when the engine cooling thermostat is left open. … The thermostat should be opened when the hot coolant starts to flow; this will quickly heat the radiator. If the radiator heats slowly, it is likely that the thermostat has been prematurely opened or stuck open.

Can you drive with P0128?

A P0128 trouble code may be displayed on your vehicle. You may not notice any issues, except the temperature gauge not reaching normal levels or the Check Engine light not being illuminated.

What is the cost of fixing P0128?

The average price for replacing an engine coolant temperature sensor is between $148 and $193. The labor costs for replacing an engine coolant temperature sensor are between $82 to $105, and parts cost between $66 and $88. The estimated cost does not include taxes or fees.

Is it serious about taking P0128 seriously?

P0128 does not represent a strict code. Suppose the vehicle is not repaired or used for a prolonged period. In that case, it is more likely that the oil may become contaminated with water, leading to engine damage and deterioration. It is possible to cause engine damage, although it would likely take many years.

How far can you drive using a P0128 Code?

One can easily say that you can drive 500 miles without worrying about the P0128 error code. It is unsafe to drive more than 1000.

Will the P0128 code be cleared by itself?

After three trips in which the Set Condition is not present, the P0128 will clear.

Can low coolant cause P0128?

Low engine cooling can cause engine temperature to drop, triggering trouble code P0128. This trouble code could also be signaled by the coolant fan, intake air temperature sensor, and coolant temperature sensor.

Will p0128 fail inspection?

Yes. Any code will. If the check engine light is on (which it is), it won’t pass.


The P0128 code indicates that the engine coolant is not getting heated up fast enough, which means that the engine’s operating temperature is not reaching a specified temperature within a given time. The ambient temperature determines time.

If the coolant is not at the right temperature, it can lead to poor engine performance and low fuel economy, which indicates that your thermostat is not working correctly.

As mentioned, there may be other causes of the code. If you get the code, take your vehicle to your mechanic for a check. You could possibly end up paying more for repairs in the long term if the damage spreads to other parts of your car.

You can prevent this from happening by diagnosing the symptoms of p0128 engine code early and fixing what is broken.

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