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Mercedes Check Engine Light Is On But Gives No Message Or Codes – Why? What To Do?

Your check engine light is on, however, the code is not shown. You're left in the dark as to what the problem is, and you need assurance that your car is still roadworthy. We have researched the problem and determined the cause of the issue.

It's possible that the Mercedes check engine light is just on because the car's fuel cap is loose or there's an issue with the code reader (check for a blown fuse in the OBD port too). Cheap code readers are hit or miss, and most are incompatible with a Mercedes-Benz. 

If it's not an issue with any of the two mentioned, you can go to your local authorized Mercedes-Benz service center and have a mechanic pull the code for you.

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Sometimes, a check engine light display doesn't mean anything is wrong and will just go away on its own. It may be just an annoyance or an indication of a serious problem. But how can you fix the problem if it's not showing any code? Read on as we discuss the problem and possible solutions. 

cool sport orange theme of mercedes interior design, Mercedes Check Engine Light Is On But Gives No Message Or Codes - Why? What To Do?

Can OBD2 Scanners Read Mercedes-Benz Error Codes?

Mercedes-Benz cars are equipped with the same OBD2 port that is used in most vehicles. However, they have a different computer system that allows them to be programmed to run in certain ways.

In addition, a Mercedes-Benz ECU may be designed to block any attempt from a scanner that is not compatible with it to read its memory. As a result, the scan will fail to provide useful information.

This is why some of these generic OBD2 error code scanners won't work with Mercedes-Benz vehicles. Even if some of them are able to read certain parts of the Mercedes-Benz vehicle's computer, they're generally not the best solution.

In addition, there's the risk of accidentally deleting all saved error codes if you're using a scanner that's incompatible with a Mercedes-Benz ECU. This can be annoying because you don't want to lose the information stored in your ECU before identifying the error codes.

The differences between the computer system on the Mercedes-Benz vehicle and the computer systems on a Toyota or Nissan vehicle make it difficult to use a generic OBD2 scanner on the Mercedes-Benz vehicle.

This is why you should use a Mercedes-Benz-specific error code scanner that is installed with compatible diagnostic software to read the codes for your car.

What Kind Of Diagnostic System Does Mercedes-Benz Use?

mercedes car interior speedometer

Mercedes-Benz is using the Xentry diagnostic system to diagnose the exact problem of its vehicle in the event of any fault. The kit is used to test for faults in engine and battery conditions, suspension, brakes, lights, airbags, and more.

Mercedes-Benz has been using this diagnostic system for many years now. But the fact that it can be hit or miss when reading Mercedes-Benz error codes with an average OBD2 scanner could mean they're trying to separate themselves from the rest of the car manufacturers.

The fact that you can only read their error codes through the Xentry diagnostic system has made people think that Mercedes-Benz is using this to create a feeling that it is a superior car manufacturer and a cut above the rest. "You're driving a Mercedes, not a Toyota!"

Some people would argue that this is a gimmick to make you feel special when it comes to your Mercedes-Benz, but they should be careful to say that since Mercedes has made its mark and the brand sells for itself and needs no sales pitch!

So, if you're looking for an error code reader that is compatible with Mercedes-Benz, then make sure it's Xentry compatible.

Check out this Mercedes-Benz compatible error code reader on Amazon.

Does A Loose Fuel Cap Cause The Check Engine Light To Illuminate?

close-car-dashboard check engine light

It's important to note that it isn't just the cap that's causing the check engine light to come on. When the fuel cap is loose, gasoline may find its way outside and evaporate freely.

Gasoline loses its combustibility when it's exposed to oxygen or air. The reason for this is that oxygen changes the chemical composition of gasoline.

When your car's ECU detects that the car is not receiving the needed combustibility from gasoline, it may trigger the check engine light to come on, thinking that there might be a problem with the fuel system.

If there's a problem with the fuel system, it's going to manifest as a malfunction in either the fuel pump or the fuel injectors not providing enough gasoline. 

How To Check And Replace Blown OBD Port Fuse

Fuses are one of those things that most people have no idea where to look to find in a vehicle. You just need to locate the fuse box which can be found under the hood.

The fuse box is a box that contains all of the fuses and wires that connect to the vehicle's electrical system.

Once you've located the fuse box, remove the dashboard panel. Once you have the panel off, look into each of the fuses and find a fuse that is labeled "LTR" which is the cigarette lighter fuse.

You will know if the fuse is blown if the metal piece that is inside the fuse has broken or burned through.

The OBD port fuse shares the same fuse as the cigarette lighter so it makes sense to check if your cigarette lighter is working before checking the fuse.

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Can A Check Engine Light Be A False Alarm?

There are times when your check engine light comes on and you wonder if you need to worry about your car. If it goes away on its own after driving for a few minutes or hours, then it may indicate that you don’t have a problem (as long as it's not flashing).

In a situation like this, you may have an oxygen sensor that needs some cleaning. But the most important thing to do is get your Mercedes-Benz-compatible error code scanner and check if it's giving any error code.

To find out the common causes of why your check engine light comes on, check the video below:

What Should You Do When Your Car's ECU Is Not Communicating With The Error Code Scanner?

In many cases, the main problem that causes a connection failure is the improper insertion of the OBD error code reader into the OBD port. Check to make sure that the cable does indeed fit into the port correctly and is snug.

Also, check the connector pins. In some cases, a broken or bent connector pin can cause a false positive. 

Another legitimate reason could be your car battery is on low voltage. A low battery voltage will often cause no communication between the car's ECU and the OBD2 error code scanner.

This is because the error code reader is not receiving enough voltage, therefore it can't read any code. Electronic gadgets operate within a specified range of voltages. For example, OBD2 readers operate at 12V and may not work if the battery is under voltage. 

How To Get Mercedes-Benz Cars Out Of Limp Mode

There are times when your car starts out fine but stops working, and sometimes it will work fine again in a short while. These are called limp modes, and they are caused by a multitude of issues ranging from simple to complex.

When you're in a vehicle that's experiencing limp mode, you may hear odd noises or see warning lights come on. This could mean that your car is in trouble and needs to be towed to the closest shop.

However, in many cases, you'll just want to wait it out until the problem goes away. You can just leave the car in the parking spot for a few minutes and wait for the engine to cool down. This is how you can easily get your car back on track when it gets into limp mode. 

If you keep driving in the car, you'll see the problem get worse over time, and the damage could become too extensive. 

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How Long Does A Mercedes-Benz Transmission System Last?

Mercedes has a reputation for making great transmissions, and it's not hard to understand why. They offer their cars with transmissions that are more efficient than the competition, which results in more efficient fuel consumption and better fuel economy.

Mercedes-Benz's transmissions are known for being robust and reliable. So, you should not be surprised if a Mercedes transmission can last up to 200,000 miles. This is despite the fact that most Mercedes owners are likely to experience wear and tear over time because of their driving behavior.

Does Low Transmission Fluid Have An Error Dashboard Light In A Mercedes?

Most Mercedes-Benz cars do not have an error dashboard light indicating that they're running low on transmission fluid. Instead, they use a dipstick to check the level of transmission fluid in the transmission system.

The dipstick is the primary way to check for transmission fluid levels. It is inserted into the transmission fluid reservoir. When the dipstick reaches the bottom, you can remove it and read the level.

The most common symptom of a transmission fluid getting low is when your car starts to miss or gets stuck when you try to change gears.

Check out this dipstick for Mercedes on Amazon.

How To Check Transmission Fluid On Mercedes

  1. Warm the engine up for about 20-25 minutes.
  2. Locate air ducts and pull them out. Disengage the clips that hold the engine cover in place and remove it.
  3. Look for the transmission fill tube and remove its cap (color black) by dislodging a red lock pin. You should find the transmission fluid tube somewhere between the engine and the firewall.
  4. Place the gear shifter either in reverse with the emergency brakes on.
  5. Insert the dipstick and check for the transmission fluid level. Refer to your car's manual for the right amount of fluid.
  6. Add transmission fluid as needed. You may have to use a funnel for this.
  7. Double-check the transmission fluid level with the dipstick.
  8. Put everything back together (fluid tube cap, red lock pin, engine cover, and air ducts).
  9. Run the engine and check if the gear shifter shifts smoothly.

If you find gray areas in the process, you may check the video below:

What Kind Of Transmission Fluid Do I Need For My Mercedes?

One of the best things you can do for your car is to use high-quality transmission fluid. Most cars are designed to use a specific transmission fluid. However, if you're not sure which one to use, a transmission fluid that is approved to be used for Mercedes cars is good enough regardless of the brand.

See this Mercedes-approved transmission fluid on Amazon.

When Should You Change Transmission Fluid In A Mercedes-Benz?

Changing your transmission fluid regularly can help prevent a costly repair. Mercedes-Benz recommends that you change your transmission fluid every 30,000 miles. 

The first signs that your transmission fluid needs to be changed are when it gets cloudy. This is because your transmission is full of iron particles which have oxidized over time.

A dirty transmission can also lead to problems like overheating or low power, and your car could be in danger.

How To Change Transmission Fluid In A Mercedes-Benz

  1. Jack up the car to elevate it and make space for you to work with.
  2. Pull out the drain plug. Make sure you have a catch basin underneath while draining the fluid.
  3. Remove the dipstick and the filter (this is also the perfect time to replace the transmission filter).
  4. You can start filling the transmission pan with new fluid once you have completely drained the old one, and don't forget to put the drain plug back on!
  5. Restart the engine, and let the new fluid run for 5 minutes or so.

In Closing

cool sport orange theme of mercedes interior design

A Mercedes check engine light that doesn't show any error code is not always a warning sign of impending doom. Sometimes it is nothing more than a loose fuel cap or an incompatible code reader.

Invest in an error code reader that's compatible with your Mercedes-Benz. You can also purchase a replacement fuel cap if you have a loose one and need to get rid of that annoying check engine light.

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