P0128 Mercedes: (Causes & Fix) How Long Can You Drive with a P0128 Code Mercedes Benz

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Find out How long can you drive with a p0128 code. The P0128 Mercedes code is an error code which is used to define a Coolant Thermostat. When you get P0128 code on your Mercedes Benz there are a couple of reasons why the code came up.

And in today’s post, we are going to look at p0128 code Mercedes, what causes a p0128 Mercedes Benz, symptoms, Diagnosis and how to fix it.

We will also answer some common question on p0128 Mercedes code like: how long can you drive with a p0128 code in Mercedes Benz and others.

So let get started with this post. Related Article: Fix a Mercedes Benz Gear Shift Stuck in Park Problem

P0128 Mercedes: (Causes & Fix) How Long Can You Drive with a P0128 Code Mercedes Benz

Meaning of P0128 Code Mercedes

The p0128 code simply indicates that the car engine coolant is not getting significantly warm and fast enough as expected.

And that means that there is an issue with the vehicle engine temperature operating system which is what is stopping it from reaching the expected rate.

The PCM (Power Train Control Module) of a vehicle tracks the duration it requires for the car engine to get to or maintain the appropriate operational temperature.

Once the car engine reaches its right functioning temperature, the PCM will order the fuel system to enter the closed-loop. This is where the calculation from the oxygen sensor is utilized to maintain and relegate efficient airflow to fuel ratio.

Normally the PCM orders the car engine coolant temp sensor to record temperature that is above 160 degrees Fahrenheit within 15 minutes from when the car engine was started.

Once the 160-degree F threshold is achieved, the recorded car engine temp has to fall below 160 degrees Fahrenheit while operating.  

The Power Train Control Module usually will record whether or not both criteria are not met. So when these issues are detected and recorded again when the engine is started, then this will trigger the P0128 code to appear.

What Causes a P0128 Mercedes Benz

There are 4 main common causes of P0128 Mercedes Benz and they are as follows:

  • A Stuck open coolant thermostat
  • Bad wiring of the coolant temp circuit
  • A bad coolant temp sensor
  •  Continuous and nonstop running of the radiator fan.

Also read: 10w40 vs 5w40 which one is better for your Car

P0128 Symptoms (What are the symptoms of the P0128 code Mercedes Benz)

Here are a few of the p0128 signs or Symptoms you will notice on your car:

  • A longer time for the vehicle to warm up
  • Display of Check Engine Light while driving
  • A high idle that is above the normal range.
  • Decrease fuel conservation and economy
  • Vehicle temperature gauge goes low than normal

Having seen some of what is, causes and symptoms of p0128 code, is it safe or okay to drive with the code on?

 That is what we will consider next and also responding to the question “how long can you drive with a p0128 code in Mercedes Benz on”.

Let’s quickly look at those.

Is it Safe to Drive with a P0128 code Mercedes?

Well, my response to this is yes.  You should be able to drive with the p0128 code on but you need to look out for your coolant temp and make plans to have the vehicle properly diagnosed and fix before proceeding on a long journey to avoid further causing more damage to your car operating system.

How long can you drive with a p0128 Code

The p0128 error code is not a serious issue, but not rectified and fixed on time, then this might lead to contamination of oil with water which can damage the car engine and then it will become serious.

So you should be able to drive some kilometres with a p0128 code. You might even go up to a 1000 mile or more with this code on. Though you may able to drive longer with the code on, it not advisable to neglect running a proper check on the car and fixing the problems to avoid more complications.

Sometime this might even require you to change the coolant thermostat or hire a mechanic to run a proper diagnose on the issue.

Or you might want to run all the check yourself when trying to save cost or if you’re that DIY kind of person. 

If that is the case, you will have to follow the diagnostic guide below, it should help you run a proper diagnosis to figure out what the problem is and how to fix the problem.

Code P0128 Diagnosis Steps

When diagnosing p0128 code, the following tools are what you will need to get going:

How to Diagnose P0128

  • Step 1

First, you have to scan your car to be sure of the p0128 code and there is no other error code.

  • Step 2

Next step you have to check for the functional state of coolant and the coolant level. If you notice a lot of rust or figured that the condition of the coolant is bad, then that could be the reason for the p0128 code.  In this case, you need to flush the entire coolant system or change the coolant.

And if happen that it is a low coolant level, then you have to fill up the coolant then you have also ensure that there are no leaks anywhere around the coolant.

  • Step 3

Next here, you have to check for the coolant temperature sensor and this can be checked with multi-meter. Normally when checking for the coolant temperature, there should be a change in the OHM readings and if was not changing, then you have to repair or replace the coolant temp sensor if it is bad.

  • Step 4

Remember I mention a stuck open thermostat above as one of the common causes of P0128 code Mercedes Benz.

If you sense or feel this may be the cause of the p0128 code on your car, then the way to diagnose this is to locate the radiator hose then you have to touch it to observe the temperature of the coolant to see how hot it is when the coolant begins to flow through the radiator hose.

Mind you, you need to be careful when doing this so you get burned.  Usually, the radiator hose should slightly warm up until the thermostat opens, only then is when to start seeing the flow of hot coolant which will warm-up the radiator hose.

If you notice that the radiator hose is heating up gradually, then that means a stuck open thermostat.

And sometimes it could also mean a premature opening of the thermostat. In this case, the thermostat needs to be changed

Common mistakes when diagnosing the P0128 code

One most common mistake car owners and some mechanic make is to replace the coolant thermostat without running a full diagnosis of the problem and checking the entire car before assuming it is the coolant thermostat.

Fine most of the time the coolant thermostat is usually the problem, but from other possible causes we considered above, you see that there are other factors that might lead to a p0128 code Mercedes, so it’s not right to make speculations and hurriedly change the thermostat without due check.

Related Article: Fix a Mercedes Benz Gear Shift Stuck in Park Problem

Answering Your Question On How Do I Fix Code P0128 Mercedes

There are three common repairs or fix for p0128 code below and these are the main ways to fix the issue.

  • First, you have to consider replacing the thermostat with new coolant or gaskets.
  • Next, you need to test drive, check and monitor the car coolant temperature
  • And finally, you have to check for any leaks around the radiator hose and coolant.

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