Question

What does the P0128 code mean?

If the P0128 code shows up, there’s a problem with your car’s coolant thermostat. The P0128 code indicates a malfunction in the coolant thermostat, i.e., the coolant temperature is below the thermostat’s regulating temperature.

If you see a P0128 error code on your OBD 2 scanner, don’t panic. Here’s what could’ve happened and how you can fix it.

The P0128 error code is often caused by a leaking cooling system or a thermostat. The thermostat keeps coolant from entering the radiator until the engine warms up to the right temperature.

This will ensure the engine reaches the optimal temperature within the set time to limit emissions. A malfunctioning thermostat prevents the optimal temperature from being achieved within the time, causing the error code to appear.  

Here are other potential causes for the error code P0128:  

• Thermostat stuck on open  
• If the engine coolant level is low   
• Malfunctioning engine coolant temperature (ECT) sensor   
• Insufficient warm-up time  

Symptoms of the P0128 code

Aside from the check engine light turning on, other signs can indicate there’s a problem 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

This is not a serious error code that needs your immediate attention. However, your engine could get damaged if you don’t fix it soon. Let’s briefly 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 in the oil. Over time, this process can ruin your car’s engine.   

The check engine light may turn on, but you can still drive your car with the P0128 code. It will not cause any hindrance or sudden shutdown of the vehicle. The only problem you’ll notice is that the temperature gauge does not reach 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.