Mercedes Eco Start/Stop Yellow - What's Wrong and How to Fix?

When your eco stop/start function is working properly on your Mercedes, you should see a green "A" with an arrow around it. And this would indicate that eco mode is ready to kick in. If your Mercedes eco stop/start light is yellow with an arrow striking across it, that would indicate that your eco stop/start function is not working properly.

Eco Start/Stop yellow light highlights

• Common reasons:start-stop can't be working, low battery, start-stop deactivated
• How to fix:wait for conditions to change, check the battery, activate start-stop manually
• Possible consequences:start-stop won't work
• Priority level:Low
• Can you drive?Yes
• DIY repair:Possible
• Repair price range:$0-$250

What Is The Mercedes Eco Start/Stop

Eco start/stop is a feature that is available in most modern Mercedes vehicles. It has received a lot of praise from Mercedes owners, but what exactly is Mercedes eco start/stop?

Automotive manufacturers are continuously aspiring to make improvements to their cars. And one of those innovative technological improvements comes in the form of the Mercedes eco start/stop. The aim of eco start/stop is to garner greater fuel efficiency and reduced emissions. 

How Does It Work

The Mercedes eco start/stop feature kicks in when your vehicle is at a temporary stop. For example, if you are idle at a red light or stuck in a traffic jam, you'll be spending quite a while in a stationary position. And during this period, your engine will continue to run even though you are not moving. During these few minutes, you'll be wasting fuel and producing unnecessary emissions.

But, switching your car off at a red light is not a valid option. This is where the Mercedes eco stop/start feature kicks in. This feature automatically switches off your engine when you are at a stop. And as you take your foot off the brake pedal, the engine seamlessly switches back allowing you to accelerate.

The successful functioning of the Mercedes eco start/stop system relies on its seamless integration with various vehicle components. The ECU plays a pivotal role as it controls the entire eco stop/start feature. It relies on various sensors to determine the engagement of the brake pedal, accelerator, battery status, etc.

The system needs to also be in sync with the battery and starter motor. The moment you take the foot off the brake, the battery supplies the power to the starter motor to restart the engine. 

Effectiveness Of Mercedes Eco Start/Stop

The primary benefit of Mercedes eco start/stop is fuel efficiency. While eliminating the need to burn fuel when stationary, you can get enhanced fuel efficiency. Depending on where and how you drive, the Mercedes eco start/stop feature can improve your fuel efficiency by up to 9%. When you burn less fuel, it directly translates to lower emissions. 

Reason Why Your Mercedes Eco Start/Stop Is Yellow

There are certain conditions that you need to meet for your Mercedes eco start/stop to function. As mentioned, when these conditions are met and the eco start/stop is ready to engage, the light will be green. But if even one of these conditions is not met, your Mercedes Eco Start/Stop will be yellow.

So, what are these conditions?

1) The Car Needs To be In Eco Mode

There are different drive modes in your Mercedes, and for the eco start/stop to work, your car should be in a certain drive mode. In most Mercedes models, the eco start/stop kicks in when you are driving in eco mode, and this can be activated by the press of a button.

In some models, instead of eco mode, you have comfort mode. If this were the case, you'd have to drive on "C". Some models come with an option for agility selection, in these models, the start/stop feature will not work when you are on "Sport+". 

So before deciding that your Mercedes eco start/stop is malfunctioning, make sure you are on the right drive mode. 

2) Engine Temperature

The engine needs to be within a certain temperature for the eco start/stop to work. If your engine is either too hot or too cold the eco start/stop will not work. This parameter exists to protect your engine. The exact window varies from model to model, but generally, it's between 60°C and 120°C, or 140°F to 250°F.

During extreme weather conditions, your Mercedes eco start/stop system may not function properly. In hot weather, the system may not shut down the engine to prevent overheating, resulting in a yellow warning light. Similarly, in freezing temperatures, the system may prioritize engine operation to maintain a comfortable cabin temperature.

3) Battery Charge

The eco start/stop relies on the battery to restart the engine. Engaging the starter motor is one of the more demanding tasks for your battery, as it significantly drains your battery. So, unless your battery is above 80%, your Mercedes eco start/stop will be yellow.

This can be commonly seen if you spend a lot of time in traffic because your battery won't get a chance to recharge. Driving for long distances at higher speeds will help your battery recharge and get the eco start/stop back in the green.

4) Cabin Settings

Depending on the temperature setting that you've set for your cabin pausing your engine might not be an option, even if you are stationary. If the engine is necessary to keep your cabin temperature in check, your Mercedes eco start/stop won't work. You'll notice the same if you've got a foggy windshield as the engine might be needed to kick in to clear the windshield. 

5) Steering Wheel Angle

Even the steering wheel angle can prompt your Mercedes eco start/stop to not activate. For the eco start/stop to work, your steering wheel angle should be below 45°. This is to ensure that you have maneuverability.

When Is Your Mercedes Eco Start/Stop Malfunctioning

The above are just a few parameters that you need to meet for your eco start/stop to function. So, it is normal if your eco start/stop is yellow occasionally. But what if it never turns green? If you notice that the Mercedes eco start/stop is always yellow and the feature is never engaged, then you probably have a malfunction.

1) Weak Battery

This is one of the main reasons why your eco start/stop gets stuck on yellow. Many Mercedes owners complain that their eco start/stop feature no longer works after using it for a few months. A weak battery is one of the common culprits if your eco stop/start is not working.

Remember, we mentioned that your battery needs to be more than 80%. With time your battery life is reduced. So, even at a full charge your battery won't exceed 80%. You might not notice the weak battery cause the rest of your electronics will be working just fine. But since the condition is not met, your Mercedes eco start/stop will not work. 

Solution:

If you suspect that your battery is weak, get your battery health assessed. This can be done at the dealership or any other automotive repair shop. Depending on the battery's condition, you can take your next step. In some cases, you might be able to service your battery and squeeze a few more miles out of it. But if your battery is too weak, replacing it might be the only option.

To make the most out of your battery, proper maintenance is key. Try to keep the terminals clean at all times. And also don't let your car sit for long periods without running.

2) Sensor Malfunctions

The Mercedes eco start/stop relies on the data from multiple sensors to function properly. The start/stop system relies on sensors to detect factors such as brake pedal engagement, engine temperature, and battery status. If the sensors are faulty, obviously your eco start/stop won't function properly.

For example, if your engine temperature sensor is sending false data, your ECU will decide that the parameters for the eco start/stop to function is not met. So, you might see a constant yellow A with an arrow striking across instead of the green light. 

Solution:

If you're encountering any complications with your sensors, it's possible that resetting them to their original settings through recalibration could prove to be a solution. Recalibration has been proven to be effective in resolving minor issues. However, if recalibration does not prove to be effective, it would be prudent to consider replacing the faulty sensor to completely restore the system's functionality.

3) Electrical Overload

The eco start/stop feature eats up a lot of battery power. And this is to be expected as the engine is switched off and re-engaged every time you come to a stop. If the electrical load on your battery is too high, your ECU might decide not to sacrifice any more battery power and disengage the Mercedes eco start/stop feature.

This could happen if multiple electrical accessories are running simultaneously. But more often than not, it's aftermarket additions that draw from your battery that cause an electrical overload. 

Solution:

To combat this issue, drivers can adopt simple practices such as minimizing the use of non-essential electrical accessories. Turning off headlights if unnecessary and avoiding blasting the AC while you are at a stop are simple solutions that can keep you from causing an electrical overload.