How to Fix the P0128 Code on Duramax (Expert Strategies)

Vehicles often show a sort of error code whenever there are some issues. Mechanics can view these codes after inspecting that something is wrong with the car due to existing symptoms.

If your car engine is showing you the code p0128 for some reason, there must be something wrong. The code p0128 means that your engine coolant temperature is lesser than the thermostat regulating temps.

But nothing to worry about. As this article will tell you the concept of the p0128 and why you view it on your Duramax engine. Therefore, without wasting time, let’s dive into the article.

Duramax P0128 Code

What Does The P0128 Code Mean On Duramax?

The code P0128 refers to the issue regarding the temperature of the coolant that is way lesser than the optimum thermostat temperature. To be more precise, there are issues prevalent with the engine coolant. This coolant isn’t getting warm enough, which is causing massive problems.

It eventually means that the engine is struggling to reach the optimum temperature for operation. For your convenience, the following is a breakdown of this code:

  • P – Powertrain, the issue is related to the engine or the gearbox.
  • 0 – The issue is generic, not from the manufacturer’s end
  • 1 –  Air/fuel mixture
  • 28 – Fault Index ( Coolant temperature lower than thermostat temperature)

How Serious Is The P0128 Code On Duramax?

Your Duramax engine showing code p0128 isn’t that critical, but there are possibilities of the engine getting damaged.

When your engine runs cold for a long time, it can result in crankcase sludge. It might also result in you getting only cool air as your heater won’t function properly when needed.

The best temperature for an engine to operate is anything above 200°F. Anything lower than this will result in a P0128 code, and it will happen the same for a Duramax engine.

There are also vehicles on which the radiator fan doesn’t have to do much even after temperatures are within 230-250°F. But on occasions where the temps are below the optimum levels, such as 150-170°, a few issues can arise.

The better option for addressing this issue is to diagnose the reason and resolve it before any significant damage is incurred.

What Causes The P0128 Code On Duramax?

There are severe reasons that can trigger the P0128 code on the Duramax engine. Mostly the issues that cause irregularity in the coolant temperatures can show this code.

But before you take any measures, you need to know the most common and specific ones. Here are some of the most common reasons for P0128:

  • Malfunctioning fan

The primary function of the radiator fan is to cool the car engine and the coolant. But if it malfunctions for some reason or is irregular while operating, there would be issues.

Mainly when the fan doesn’t function as it is supposed to, it results in the slow heating of the coolant.

  • Inadequate Coolant

The quality and coolant level can also be a reason behind the P0128 code. In no situation, the level of coolant should be lower. When there is the inadequacy of the coolants, it becomes one of the prime reasons behind thermostat sticking. In addition to this, the dirty coolant also has a huge part in this.

  • Faulty Sensor

If the sensors responsible for taking the accurate reading for the temperature are faulty, you will see the P0128 code more often. The poor wiring and the error-prone sensor can show this code to you, even if there is nothing wrong with the engine coolant.

  • Malfunctioning PCM

The issues with the PCM are not very common. It rarely happens, but when there is such an occurrence, you will notice the frequent showing of the code.

Such occurrences mainly accelerate due to software updates full of bugs or the need for an immediate update.

Resolving these above-mentioned issues will result in fixing the error code p0128. But for mitigating most of these problems, you would need mechanic assistance. It will cost you extra money along with the price for components that need replacement.

How To Fix The P0128 Code On Duramax?

It is possible to fix the P0128 code at home without expert assistance. If you want, you can cut off the extra mechanic cost that you would need. And for this coolant level, you need to follow the steps mentioned below:

Step – 1: Confirm the Error

The first step should always be to confirm whether the error exists. Assumptions about the error don’t mean anything until you have conclusive evidence.

That is why you need to use an OBDII scanner. All you need to do is connect the scanner to your vehicle’s system and then do the scanning.

When it’s done, you will see the error code numbers that portray the issues in your vehicle with the Duramax engine.

Step – 2: Examine ECT Sensor

ECT sensors are usually hooked up with the thermostat. And that said, if they are faulty or damaged, they need replacement.

Firstly, you need to locate it to determine whether it has any damages. You may use a multimeter to evaluate whether its output is up to the mark.

If you see that the resistance isn’t in the range of 2000-3000, you have to replace it.

Step – 3: Inspect Thermostat

You have to check whether the thermostat is working correctly or not. But before checking, make sure that you are very cautious as the engine is too hot.

If the thermostat has issues, you need to replace it with a new one. While setting up the new one, place it accurately and carefully connect its end with the engine.

Step – 4: Clear the Error Code

After you have rechecked and resolved every issue, you need to start the process of clearing the code manually.

Here, again you must use the OBDII scanner to clear the codes and initiate the command by asking the scanner to clear out inactive codes.

When the clearing is done, recheck whether the problem is resolved or not by performing another scan. If the issue persists, better opt for a mechanic.

Other Symptoms Of Getting P0128 On Duramax

You already know the causes and implications of the P0128 code. But some additional symptoms might result in a P0128 code in the Duramax engine. Here are some of the prominent ones:

  • High Fuel Consumption
  • Temps dropping at high speed
  • More time is required to reach optimum engine temperature
  • Poor heater output

How Much Does It Cost To Fix The Duramax P0128 Code?

It is possible to fix the P0128 code at home by yourself, but not all the time; outcomes would be effective.

If you fix it at home, you may need the cost to replace the thermostat ranging around $15-300. At the same time, the price of an ECT sensor might range from around $300-320.

The labor costs for replacing a thermostat are around $150-300, and for an ECT sensor, about $100.

Can You Drive Your Duramax With Code P0128?

There will be no significant issues if you drive the car with the Duramax engine for a considerable period.

If the temperature level is around 170-180 F, it’s no issue. But once it drops below 150 F, you need to take it seriously as it can have adverse effects on the engine health.


Issues with the engines are prevalent, and they need to be addressed immediately. Your car with the Duramax engine is susceptible to issues unless you take good care of it.

If you figure out the engine showing the P0128 error code, it’s better to take some time and properly investigate it. Once you are confirmed, only then should you take action to resolve it.  With that being said, this article emphasizes the identification and the fix of the P0128 code.

Moreover, the main aim of this article was to let you know about the code and its fix. We hope that we have been able to meet your needs, and if there is any confusion, do let us know.

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