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Can low coolant cause code P0128?

Yes, low coolant levels can potentially cause the diagnostic trouble code (DTC) P0128 to be set in a vehicle's engine control module (ECM). This code indicates that the engine coolant temperature is not reaching the expected operating temperature within a specified time after the engine is started.


What is Code P0128?


Code P0128 is a generic diagnostic trouble code that indicates the engine coolant temperature (ECT) did not reach the expected operating temperature within a specified time after the engine was started. This code is set when the ECM detects that the coolant temperature is lower than the expected temperature range for normal engine operation.


The P0128 code is typically triggered when the engine coolant temperature does not reach a certain threshold, usually around 195-210°F (91-99°C), within a predefined time after the engine is started from a cold condition. This could be caused by a variety of issues, including low coolant level, a faulty thermostat, a problem with the cooling system, or a malfunctioning ECT sensor.


How Can Low Coolant Cause Code P0128?


One of the primary causes of the P0128 code is a low coolant level in the vehicle's cooling system. When the coolant level is low, the engine may not be able to reach the expected operating temperature within the specified time frame. This is because the reduced amount of coolant circulating through the system cannot effectively absorb and transfer heat away from the engine.



  • Insufficient Coolant Flow: With a low coolant level, the water pump may not be able to circulate the coolant through the engine and radiator efficiently, leading to poor heat transfer and slower warm-up times.

  • Increased Coolant Temperature Fluctuations: A low coolant level can cause the coolant temperature to fluctuate more, making it difficult for the ECM to accurately determine when the engine has reached the expected operating temperature.

  • Potential Overheating: In extreme cases, a low coolant level can lead to overheating, which can also trigger the P0128 code as the engine is unable to reach the proper operating temperature.


It's important to note that while low coolant is a common cause of the P0128 code, there can be other underlying issues, such as a faulty thermostat, a problem with the cooling system, or a malfunctioning ECT sensor. A thorough diagnosis by a qualified mechanic is recommended to determine the root cause of the problem.

How does a car act when coolant is low?


Low coolant also causes your engine to burn fuel more quickly. You will notice symptoms such as poor fuel economy, a loss of acceleration, and the car's high-temperature gauge getting close to the red if your car is low on coolant. All of these signs mean that you should put more coolant into your car.



Does a coolant temperature sensor affect a thermostat?


No, the thermostat works off the heat of the water passing through it. A coolant temperature sensor might control the electric cooling fans though.



How long can I drive with a P0128 code?


How Long Can You Drive with a P0128 Code? Although it may be possible to drive short distances with code P0128 set, you should get the issue fixed by a professional right away. Doing so will help ensure your vehicle keeps running at its best while also helping to prevent any additional damage.



What happens when coolant temperature sensor goes bad?


Black smoke coming out of your car's exhaust pipe could be another indication that your car's coolant temperature sensor is faulty or failing. Here's what happens: Faulty readings from the coolant temperature sensor can cause the engine to miscalculate the air-fuel mix in the engine.



Can low coolant cause a check engine?


Low coolant levels affect engine temperature, causing the sensor to trigger a false reading and light up the 'Check Engine' or coolant warning sign. A sweet “burn off” smell can suggest that there is a coolant leak. Low coolant levels which require replacing the coolant more often than usual.



Will the P0128 code clear itself?


This is referred to as a permanent code. This permanent code will go away on its own after the monitor runs and passes. Until then it will be present but only when read with a scan tool and will not turn the light on. If the problem Is detected again by the computer it will first set a pending code.



Can low coolant cause P0128 code?


Low engine coolant can alter the engine running temperature enough to signal trouble code P0128. Your intake air temperature sensor, coolant temperature sensor and coolant fan could also signal this trouble code, so these should be inspected after you look over your thermostat and coolant level.



What happens if you drive with very low coolant?


What happens if I drive my car with no coolant? If you ignore these signs and continue to drive your car without coolant, your engine parts will get badly damaged – maybe even permanently – due to overheating. That is why it is very dangerous to drive your car when you are low on coolant.



Can low coolant cause a thermostat code?


Low engine coolant can alter the engine running temperature enough to signal trouble code P0128. Your intake air temperature sensor, coolant temperature sensor and coolant fan could also signal this trouble code, so these should be inspected after you look over your thermostat and coolant level.



How to fix coolant temperature below thermostat regulating temperature?


Repairing the P0128 error code

  1. Replacing a faulty thermostat that is stuck open and doesn't allow coolant to reach proper temperature.
  2. Repairing or replacing the coolant temperature sensor if it's found to be faulty.
  3. Topping up or replacing engine coolant if levels are low or if the coolant is in poor condition.


Kevin's Auto

Kevin Bennett

Company Owner

Kevin Bennet is the founder and owner of Kevin's Autos, a leading automotive service provider in Australia. With a deep commitment to customer satisfaction and years of industry expertise, Kevin uses his blog to answer the most common questions posed by his customers. From maintenance tips to troubleshooting advice, Kevin's articles are designed to empower drivers with the knowledge they need to keep their vehicles running smoothly and safely.