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P0128 Code: Causes, Symptoms and How to Fix it

  • Car Care Tips
  • Renee Martin
  • 3 minutes

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Do you have the P0128 error code on your OBD 2 scanner? From what does the P0128 code mean and how to fix it, we have explained all you need to know in this post.   

What does the P0128 code mean? 

The P0128 is a diagnostic trouble code (DTC) for malfunction in coolant thermostat – coolant temperature below the thermostat regulating temperature. In simple terms, when the code shows up, there’s a problem with your car’s coolant thermostat. 

What causes the P0128 code?   

A leaking cooling system or a thermostat is most often the reason for the error code. The role of the thermostat is to prevent the coolant from entering the radiator until the engine reaches the right temperature.

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This will ensure the engine reaches the optimal temperature within the set time to limit emissions. In a malfunctioning thermostat, the optimal temperature cannot be achieved within the time, and this causes the error code to appear.  

Here are other potential causes for the error code:  

  • Thermostat stuck open  
  • If the engine coolant level is low   
  • Malfunction in Engine Coolant Temperature (ECT) sensor   
  • Insufficient warm-up time  

P0128 Code

What are the symptoms of the P0128 code?   

Other than the check engine light turning on, here are other symptoms that can tell when there’s something wrong with the coolant thermostat:   

  • When the idle is higher than the usual  
  • If the temperature gauge remains low  
  • Reduced fuel efficiency  
  • The vehicle takes too long to warm up  
  • Fluctuating engine temperature 

How serious is the P0128 code?   

This is not a serious error code that needs your immediate attention. However, there’s a chance of your engine getting damaged if you don’t get it soon. Let’s shortly explain how this happens. If the coolant does not get hot enough, there won’t be enough heat to burn the condensation, leading to water ending up on oil. Over time, this process can ruin your car’s engine.   

Is it safe to drive with the P0128 code?   

The code will illuminate the check engine light, but you can still drive your car. It will not cause any hindrance or sudden shutting down of the vehicle. The only problem you’ll notice is the temperature gauge not reaching the optimal levels. But, over time, this can damage your car’s engine and performance. So, it’s always best to get it checked by a professional.  

How long can I drive with this issue?  

As we mentioned earlier, since this is not a serious issue, you can drive your car indefinitely. It won’t make your car stop all of a sudden. You can comfortably drive with this issue. However, in the long term, it can cause expensive damages.   

How can you fix the P0128 issue?   

It’s always best to seek the help of an expert to fix the issue. The professional could ask you to do the following replacement or repairs:  

  • They might ask you to replace the thermostat   
  • Replace the coolant temperature sensor or the wiring and other components of the damaged sensor  

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How much does it cost to fix the P0128 issue?  

It will cost you anywhere between $400 to $800 to fix this issue. You’ll be spending close to $75 to $100 for labor and up t0 $600 to change the damaged components.   

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