Seeing the dreaded “Check coolant level see operator’s manual” message coming on your Mercedes instrument cluster can be concerning, especially if you don’t know what it really means.
In this article, I am going to explain what this alert means, the main causes, and how to fix the issue. Let’s get into it!
What Does a Coolant Do on a Mercedes?
Before diving into the warning light, it’s helpful to understand what coolant (also called antifreeze) does for your Mercedes-Benz.
This liquid mixture of water and ethylene glycol keeps your engine running at optimal temperature by circulating through passages drilled in the engine block and cylinder head.
Coolant performs a few vital jobs. First, it absorbs excess heat from the combustion process and hot engine parts.
It whisks this heat away to the radiator, where it can be dispersed to the outside air, preventing components from overheating.
Secondly, coolant lowers the freezing point of the water-based mixture well below water’s normal 32°F freezing point.
This antifreeze effect protects the cooling system from rupture or cracks in frigid winter temperatures.
Finally, coolant raises the boiling point, allowing the liquid to operate safely at temperatures well above water’s normal 212°F boiling point without evaporating away.
Maintaining proper coolant levels and coolant health is mandatory to protect your Mercedes’ sophisticated engine.
What Does “Check Coolant Level” Mean on a Mercedes?
When the “check coolant level” alert pops up on a Mercedes dashboard, it means that the car’s computer has detected a potential problem with the coolant system.
More specifically, it signals that the coolant level may be too low for the system to function correctly.
This warning relies heavily on a coolant level sensor located in the coolant reservoir. This sensor monitors the amount of coolant present in the system and sends this data to the vehicle’s computer system.
If the coolant level falls below a predefined threshold, the computer triggers the warning alert to inform you.
What Causes the “Check Coolant Level” Alert on a Mercedes Benz to Come On?
Based on my experience as a mechanic, there are several scenarios that can lead to the “check coolant level” warning coming on; these include:
Low Coolant Level Due to Normal Usage
The most common cause of this message is low coolant levels due to usage.
Over time, the level of coolant in a car can naturally decrease due to evaporation or small leaks. Regular top-ups are required to maintain an adequate coolant level.
A more serious cause is a leak in the coolant system. The common areas to look for leaks in a Mercedes are the coolant tank, coolant reservoir cap, radiator, and hoses.
Cracks or damages in any of these components can lead to significant coolant loss, triggering the warning.
Bad Coolant Level Sensor
Sometimes, the coolant level may be fine, but the sensor itself is faulty.
A malfunctioning sensor may send incorrect readings to the computer, causing it to trigger the warning erroneously.
Faulty Windshield Washer Sensor
Here is a fun fact, a faulty windshield washer sensor can sometimes cause the coolant level warning to come on.
This anomaly is because, in most Mercedes models, the windshield washer sensor and coolant level sensor are wired in the same circuit. so, if one sensor fails, it may interfere with the operation of the other.
How to Fix and Reset Mercedes “Check Coolant Level” Message
Now that I have explained the leading causes for this warning, let’s look at how to go about fixing the issue.
1. Check the Coolant Level (Top it Up)
The first thing I recommend is checking the coolant reservoir to see if the antifreeze is really low. If it is, top it up. As an auto technician, I recommend using any Mercedes OEM coolant or any G40-spec coolant.
After adding more coolant, turn off your Mercedes and turn it on again. The message should automatically clear once the level sensor has reset.
2. Change the Coolant Level Sensor
If you check the coolant expansion tank and find there is more than enough coolant, then the problem might be a malfunctioning coolant level sensor found at the bottom of the water bottle (coolant tank).
In this case, you will need to replace the coolant level sensor.
I personally recommend changing the whole coolant reservoir rather than just the sensor, since it will come with a new sensor and a new cap.
3. Change the Windshield Washer Fluid Sensor
As I mentioned above, the windshield washer fluid level sensor can cause your Mercedes to display a “check coolant level” message.
If you changed the coolant bottle and added enough coolant but still got the warning, the next step is to change this sensor. In most cases, this should solve the problem.
4. Do a Coolant Pressure Test
If the three above steps don’t fix the coolant warning message, then its time to take your car to the nearest Mercedes dealer or any qualified independent garage.
The Technicians there will perform a coolant pressure test to identify leaks, fix the coolant leaks and reset the “check coolant level see operator’s manual” warning from your dashboard.