Mercedes Benz Eco Start Stop Not Working: Causes & Solutions

1. Understanding the Mercedes Benz Eco Start Stop System

The Mercedes Benz Eco Start Stop system, also known as automatic start stop (ASS), is designed to improve fuel efficiency and reduce emissions. When the vehicle comes to a complete stop, such as at a traffic light, the engine automatically shuts off. When the driver releases the brake pedal, the engine restarts seamlessly, allowing for immediate acceleration. This system relies on a complex network of sensors, control modules, and a robust battery system to function correctly.

1.1. Key Components of the System

• Main Battery: Provides power for starting the engine and running vehicle accessories.
• Auxiliary Battery (or Capacitor): Supplies power to maintain electrical systems during engine shutdown and assists with restarting the engine. Some models use a capacitor instead of a battery.
• Starter Motor: A heavy-duty starter motor is used, designed for the frequent starts and stops.
• Sensors: Various sensors monitor vehicle speed, engine temperature, battery charge, and other parameters.
• Control Module: The central control unit that manages the start-stop system based on sensor inputs.

1.2. How the System Works

1. Activation Conditions: The system only activates when certain conditions are met, such as the engine being at operating temperature, the battery having sufficient charge, and the vehicle being at a complete stop.
2. Engine Shutdown: Once all conditions are met, the engine shuts off automatically when the brake pedal is depressed.
3. Restarting the Engine: When the brake pedal is released, or the steering wheel is turned, the engine restarts quickly and smoothly.
4. Deactivation: The driver can manually deactivate the system using a button on the dashboard. The system may also deactivate automatically under certain conditions, such as when the climate control system requires more power.

Mercedes Benz Eco Start/Stop button location, typically on the center console.

2. Common Reasons Why the Eco Start Stop System Isn’t Working

Several factors can cause the Mercedes Benz Eco Start Stop system to malfunction. Addressing these issues promptly can help restore the system’s functionality and maintain your vehicle’s fuel efficiency.

2.1. Insufficient Battery Charge

A low battery charge is one of the most common reasons for the Eco Start Stop system to fail. The system requires a certain voltage level to operate correctly.

• Main Battery: If the main battery is old or not adequately charged, the system will likely be disabled.
• Auxiliary Battery: The auxiliary battery, responsible for supporting electrical functions during engine shutdown, can also be a culprit. A weak auxiliary battery will prevent the system from working. Some Mercedes-Benz models use a capacitor instead of an auxiliary battery.

2.2. Battery Age and Condition

Batteries degrade over time and lose their ability to hold a charge. An aging battery may still start the car but may not have enough capacity to support the Eco Start Stop system.

2.3. Sensor Malfunctions

The Eco Start Stop system relies on various sensors to monitor operating conditions. A faulty sensor can send incorrect data to the control module, preventing the system from activating.

• Crankshaft Position Sensor: This sensor monitors the engine’s rotational speed and position. A faulty sensor can prevent the engine from restarting.
• Battery Sensor: This sensor monitors the battery’s voltage and temperature. If the sensor detects low voltage or extreme temperatures, it may disable the Eco Start Stop system.
• Brake Pedal Sensor: This sensor detects when the brake pedal is pressed. If the sensor is faulty, the system may not recognize when the vehicle is stopped.

2.4. Engine Temperature

The Eco Start Stop system typically only activates when the engine has reached its optimal operating temperature. If the engine is too cold or too hot, the system will remain inactive to protect the engine.

2.5. Climate Control Settings

The system may be disabled if the climate control system is set to a high setting, such as maximum cooling or heating. This is because the engine needs to run to provide sufficient power for the climate control system.

2.6. Diagnostic Trouble Codes (DTCs)

Stored DTCs related to the Eco Start Stop system can indicate underlying issues. Scanning the vehicle’s computer system with a diagnostic tool can reveal these codes and help pinpoint the problem.

2.7. Software Issues

In some cases, software glitches or outdated software can cause the Eco Start Stop system to malfunction. Updating the vehicle’s software may resolve these issues.

2.8. System Overrides

The system can be temporarily disabled due to various conditions, such as when the vehicle is on an incline, the steering wheel is turned sharply, or the driver is making frequent stops and starts in heavy traffic.

2.9. Other Electrical Issues

Electrical problems, such as faulty wiring or loose connections, can disrupt the Eco Start Stop system. Inspecting the electrical connections and wiring related to the system can help identify and resolve these issues.

3. Step-by-Step Troubleshooting Guide

If your Mercedes Benz Eco Start Stop system is not working, follow these steps to troubleshoot the problem.

3.1. Check the Battery Voltage

Use a multimeter or a battery tester to check the voltage of both the main and auxiliary batteries.

1. Prepare the Vehicle: Turn off the engine and all electrical accessories.
2. Locate the Batteries: The main battery is usually located in the engine compartment or the trunk. The auxiliary battery may be located under the rear seat or in the engine compartment.
3. Connect the Multimeter: Connect the positive (red) lead of the multimeter to the positive terminal of the battery and the negative (black) lead to the negative terminal.
4. Read the Voltage: Check the voltage reading on the multimeter. A fully charged 12V battery should read around 12.6 volts or higher. If the voltage is below 12 volts, the battery may be discharged or failing.

Using a multimeter to check the battery voltage on a car battery.

3.2. Charge the Battery

If the battery voltage is low, use a battery charger to fully charge both the main and auxiliary batteries.

1. Connect the Charger: Connect the battery charger to the battery terminals, following the manufacturer’s instructions.
2. Set the Charging Mode: Select the appropriate charging mode for your battery type (e.g., standard, AGM, gel).
3. Charge the Battery: Allow the battery to charge fully. This may take several hours, depending on the battery’s condition and the charger’s output.
4. Monitor the Progress: Periodically check the battery voltage to ensure it is increasing.

3.3. Test the Battery Load

A load test can determine the battery’s ability to deliver power under load.

1. Use a Load Tester: Connect a load tester to the battery terminals.
2. Apply the Load: Apply a load to the battery, following the tester’s instructions.
3. Monitor the Voltage: Observe the voltage reading on the tester. The voltage should remain above a certain level (usually around 9.6 volts) for a specified period.
4. Interpret the Results: If the voltage drops too low or too quickly, the battery may be failing and need to be replaced.

3.4. Check Sensor Connections

Inspect the connections to the various sensors involved in the Eco Start Stop system, such as the crankshaft position sensor, battery sensor, and brake pedal sensor.

1. Locate the Sensors: Refer to your vehicle’s service manual to locate the sensors.
2. Inspect the Connections: Check the sensor connectors for corrosion, damage, or loose connections.
3. Clean and Secure: Clean any corroded connectors with a wire brush and electrical contact cleaner. Ensure that the connectors are securely attached to the sensors.

3.5. Scan for Diagnostic Trouble Codes (DTCs)

Use an OBD-II scanner to check for any DTCs related to the Eco Start Stop system.

1. Connect the Scanner: Plug the OBD-II scanner into the vehicle’s diagnostic port, usually located under the dashboard.
2. Turn on the Ignition: Turn the ignition key to the “on” position, but do not start the engine.
3. Read the Codes: Follow the scanner’s instructions to read any stored DTCs.
4. Interpret the Codes: Refer to a DTC code list or your vehicle’s service manual to interpret the codes. Common codes related to the Eco Start Stop system include:
   • B1834: Starter motor circuit fault
   • P0571: Cruise control/brake switch A circuit malfunction
   • P0615: Starter relay circuit

An OBD-II scanner connected to a car’s diagnostic port.

3.6. Clear the Codes and Test the System

After addressing any issues, clear the DTCs using the OBD-II scanner and test the Eco Start Stop system to see if it is functioning correctly.

1. Clear the Codes: Follow the scanner’s instructions to clear the stored DTCs.
2. Test the System: Start the engine and drive the vehicle under conditions that should activate the Eco Start Stop system (e.g., engine at operating temperature, sufficient battery charge).
3. Observe the System: Monitor the system to see if it shuts off the engine when the vehicle comes to a stop and restarts it when the brake pedal is released.

3.7. Check the Auxiliary Battery (or Capacitor)

The auxiliary battery (or capacitor) supports the electrical systems during engine shutdown and assists with restarting the engine.

1. Locate the Auxiliary Battery: The auxiliary battery is usually located under the rear seat or in the engine compartment.
2. Test the Voltage: Use a multimeter to check the voltage of the auxiliary battery. A fully charged auxiliary battery should read around 12.6 volts or higher.
3. Check the Capacitor: If your vehicle uses a capacitor instead of an auxiliary battery, follow the manufacturer’s instructions for testing its functionality.

3.8. Update the Software

Outdated software can cause issues with the Eco Start Stop system. Check for any available software updates for your vehicle and install them following the manufacturer’s instructions.

3.9. Consult a Professional

If you have followed these steps and the Eco Start Stop system is still not working, it may be necessary to consult a professional mechanic or technician. They can perform more advanced diagnostics and repairs.

4. Advanced Diagnostic Procedures

For more complex issues, advanced diagnostic procedures may be required.

4.1. Using a Mercedes-Benz STAR Diagnostic System

The Mercedes-Benz STAR Diagnostic System is a specialized tool used by Mercedes-Benz technicians to diagnose and repair vehicle systems.

1. Connect the System: Connect the STAR Diagnostic System to the vehicle’s diagnostic port.
2. Run Diagnostics: Follow the system’s instructions to run a comprehensive diagnostic scan.
3. Interpret the Results: The STAR Diagnostic System can provide detailed information about the Eco Start Stop system, including sensor data, fault codes, and system status.
4. Perform Guided Tests: The system can also guide technicians through specific tests to pinpoint the cause of the problem.

4.2. Checking the Starter Motor

The starter motor is responsible for restarting the engine after it has been shut off by the Eco Start Stop system.

1. Inspect the Starter Motor: Check the starter motor for any signs of damage or wear.
2. Test the Starter Motor Circuit: Use a multimeter to test the starter motor circuit for voltage and continuity.
3. Replace the Starter Motor: If the starter motor is faulty, it may need to be replaced.

4.3. Verifying Sensor Data

Accurate sensor data is crucial for the Eco Start Stop system to function correctly.

1. Monitor Sensor Data: Use a diagnostic tool to monitor the data from the various sensors involved in the system, such as the crankshaft position sensor, battery sensor, and brake pedal sensor.
2. Compare to Specifications: Compare the sensor data to the specifications in your vehicle’s service manual.
3. Identify Discrepancies: Identify any discrepancies between the sensor data and the specifications. This can help pinpoint faulty sensors or other issues.

5. Maintaining the Eco Start Stop System

Regular maintenance can help prevent issues with the Eco Start Stop system and ensure its longevity.

5.1. Regular Battery Maintenance

Proper battery maintenance is essential for the Eco Start Stop system.

1. Keep the Battery Clean: Clean the battery terminals and connections regularly to prevent corrosion.
2. Check the Battery Voltage: Periodically check the battery voltage to ensure it is within the recommended range.
3. Charge the Battery: If the battery voltage is low, use a battery charger to fully charge the battery.
4. Replace the Battery: Replace the battery every 3-5 years, or as recommended by the manufacturer.

5.2. Software Updates

Keep your vehicle’s software up to date to ensure optimal performance of the Eco Start Stop system.

1. Check for Updates: Check for software updates regularly.
2. Install Updates: Install any available software updates following the manufacturer’s instructions.

5.3. Professional Inspections

Schedule regular inspections with a qualified mechanic or technician to check the Eco Start Stop system and other vehicle systems.

1. Schedule Inspections: Schedule inspections at least once a year, or as recommended by the manufacturer.
2. Address Issues: Address any issues identified during the inspections promptly to prevent further damage.

6. Benefits of a Properly Functioning Eco Start Stop System

A properly functioning Eco Start Stop system offers several benefits.

6.1. Improved Fuel Efficiency

The primary benefit of the Eco Start Stop system is improved fuel efficiency. By shutting off the engine when the vehicle is stopped, the system reduces fuel consumption and lowers emissions.

6.2. Reduced Emissions

The Eco Start Stop system helps reduce emissions by minimizing the amount of time the engine is idling.

6.3. Enhanced Driving Experience

The system provides a seamless and smooth driving experience. The engine restarts quickly and smoothly, allowing for immediate acceleration.

6.4. Cost Savings

By improving fuel efficiency and reducing emissions, the Eco Start Stop system can help save money on fuel costs and reduce your environmental impact.

7. Potential Issues with Disabling the Eco Start Stop System

While it may be tempting to disable the Eco Start Stop system if it is not working correctly, there are potential issues to consider.

7.1. Reduced Fuel Efficiency

Disabling the system will result in reduced fuel efficiency, as the engine will continue to run while the vehicle is stopped.

7.2. Increased Emissions

Disabling the system will increase emissions, as the engine will idle for longer periods.

7.3. Potential Damage to the Starter Motor

The Eco Start Stop system uses a heavy-duty starter motor designed for frequent starts and stops. Disabling the system may result in increased wear and tear on the starter motor.

7.4. Voiding Warranty

Disabling the system may void your vehicle’s warranty, as it is designed to be used as part of the vehicle’s emissions control system.

8. How to Find Reliable Diagnostic Tools at CARDIAGTECH.NET

When troubleshooting a Mercedes Benz Eco Start Stop system, having the right diagnostic tools is crucial. CARDIAGTECH.NET offers a range of high-quality tools to help you accurately diagnose and resolve issues.

8.1. Car Battery Testers

A car battery tester is an essential tool for checking the health and performance of your vehicle’s battery. CARDIAGTECH.NET offers a variety of battery testers to suit different needs and budgets.

• Digital Battery Testers: These testers provide accurate voltage, resistance, and CCA (Cold Cranking Amps) readings.
• Load Testers: These testers simulate the load on the battery to determine its ability to deliver power under load.
• Conductance Testers: These testers use conductance technology to assess the battery’s overall health without applying a load.

8.2. OBD-II Scanners

An OBD-II scanner is necessary for reading and clearing diagnostic trouble codes (DTCs) from your vehicle’s computer system. CARDIAGTECH.NET offers a range of OBD-II scanners, from basic code readers to advanced diagnostic tools.

• Basic Code Readers: These scanners can read and clear DTCs, providing basic diagnostic information.
• Advanced Diagnostic Tools: These scanners offer advanced features such as live data streaming, component testing, and bi-directional control.

8.3. Multimeters

A multimeter is a versatile tool for measuring voltage, current, and resistance in electrical circuits. CARDIAGTECH.NET offers a range of multimeters suitable for automotive use.

• Digital Multimeters: These multimeters provide accurate and easy-to-read measurements.
• Analog Multimeters: These multimeters use a needle and scale to display measurements.

8.4. Why Choose CARDIAGTECH.NET?

• High-Quality Products: CARDIAGTECH.NET offers high-quality diagnostic tools from trusted brands.
• Competitive Prices: We offer competitive prices on all our products.
• Expert Support: Our team of experts can help you choose the right tools for your needs and provide technical support.
• Fast Shipping: We offer fast shipping on all orders.
• Customer Satisfaction: We are committed to customer satisfaction and offer a money-back guarantee.

A selection of car diagnostic tools available at CARDIAGTECH.NET.

9. Real-World Scenarios and Solutions

Understanding how the Eco Start Stop system behaves in different situations can help you diagnose and resolve issues more effectively.

9.1. Scenario 1: System Not Working After a Long Drive

Problem: The Eco Start Stop system is not working even after a long drive, which should have fully charged the battery.

Possible Causes:

• Faulty auxiliary battery: The auxiliary battery may not be holding a charge, even if the main battery is fully charged.
• Sensor malfunction: A faulty sensor, such as the battery sensor or crankshaft position sensor, may be preventing the system from activating.
• Software issue: A software glitch or outdated software may be causing the problem.

Solutions:

1. Check the auxiliary battery: Test the voltage of the auxiliary battery to ensure it is within the recommended range.
2. Scan for DTCs: Use an OBD-II scanner to check for any DTCs related to the Eco Start Stop system.
3. Update the software: Check for and install any available software updates for your vehicle.
4. Consult a professional: If the problem persists, consult a professional mechanic or technician for further diagnosis and repair.

9.2. Scenario 2: System Works Intermittently

Problem: The Eco Start Stop system works sometimes but not others.

Possible Causes:

• Marginal battery charge: The battery may be holding just enough charge to sometimes activate the system.
• Loose connections: Loose or corroded electrical connections may be causing intermittent issues.
• Temperature sensitivity: The system may be more sensitive to temperature changes, working better in certain conditions.

Solutions:

1. Check battery connections: Inspect and clean all battery terminals and connections.
2. Monitor battery voltage: Monitor the battery voltage over time to see if it drops below the required level.
3. Test sensor connections: Check the connections to the various sensors involved in the Eco Start Stop system.
4. Consult a professional: If the problem persists, consult a professional mechanic or technician for further diagnosis and repair.

9.3. Scenario 3: System Disables When Using Climate Control

Problem: The Eco Start Stop system disables when the climate control system is set to a high setting.

Possible Causes:

• High electrical load: The climate control system draws a significant amount of power, which can disable the Eco Start Stop system.
• Battery capacity: The battery may not have enough capacity to support both the climate control system and the Eco Start Stop system.

Solutions:

1. Adjust climate control settings: Try reducing the climate control settings to see if the system activates.
2. Check battery capacity: Ensure that the battery has sufficient capacity to support the electrical load.
3. Upgrade battery: Consider upgrading to a higher-capacity battery to support the electrical load.
4. Consult a professional: If the problem persists, consult a professional mechanic or technician for further diagnosis and repair.

10. Expert Tips for Maintaining Your Mercedes Benz Eco Start Stop System

To keep your Mercedes Benz Eco Start Stop system in optimal condition, consider these expert tips:

10.1. Keep Your Battery Healthy

• Regularly check the battery voltage: Ensure it stays within the recommended range.
• Clean battery terminals: Prevent corrosion for optimal conductivity.
• Use a battery maintainer: Especially during periods of infrequent use.

10.2. Stay Updated with Software

• Check for updates regularly: Outdated software can lead to system malfunctions.
• Install updates promptly: Follow the manufacturer’s instructions carefully.

10.3. Drive Regularly

• Avoid prolonged periods of inactivity: Regular driving helps maintain battery charge.
• Take longer drives occasionally: This ensures the battery gets fully charged.

10.4. Address Issues Promptly

• Don’t ignore warning signs: Address any unusual behavior or error messages immediately.
• Consult professionals when needed: For complex issues, seek expert advice.

10.5. Use Quality Diagnostic Tools

• Invest in reliable tools: Accurate diagnostics are essential for effective repairs.
• Consider CARDIAGTECH.NET: For high-quality tools and expert support.

11. The Future of Eco Start Stop Systems

As automotive technology advances, Eco Start Stop systems are becoming more sophisticated and efficient. Future systems may incorporate:

11.1. Enhanced Battery Technology

• Lithium-ion batteries: Offering higher energy density and longer lifespan.
• Advanced energy management systems: Optimizing battery usage and charging.

11.2. Improved Sensor Integration

• More accurate sensors: Providing precise data for system control.
• Predictive algorithms: Anticipating stops and starts for smoother transitions.

11.3. Seamless Integration with Hybrid and Electric Vehicles

• Combining start-stop with regenerative braking: Maximizing energy efficiency.
• Optimized performance in hybrid and electric drivetrains: Enhancing overall efficiency.

11.4. Over-the-Air Updates

• Remote software updates: Ensuring systems are always up-to-date.
• Real-time diagnostics: Monitoring system performance and identifying potential issues.

12. Frequently Asked Questions (FAQs)

Q1: Why did my Mercedes Eco Start Stop stop working?

A: Common reasons include low battery charge, faulty sensors, engine temperature, climate control settings, and diagnostic trouble codes.

Q2: How do I reset my Mercedes Eco Start Stop?

A: Try charging the battery, checking sensor connections, and clearing diagnostic trouble codes. If the problem persists, consult a professional.

Q3: Can I disable the Eco Start Stop system permanently?

A: Yes, but it may result in reduced fuel efficiency, increased emissions, and potential warranty issues.

Q4: How much does it cost to fix the Eco Start Stop system?

A: The cost varies depending on the issue. Battery replacement can range from $200 to $500, while sensor replacements can cost between $100 and $300.

Q5: What is the auxiliary battery for in Mercedes?

A: The auxiliary battery supports electrical systems during engine shutdown and assists with restarting the engine.

Q6: How do I know if my auxiliary battery is bad?

A: Check the voltage with a multimeter. A reading below 12.6 volts indicates a potential issue.

Q7: Where is the auxiliary battery located in my Mercedes?

A: It’s typically located under the rear seat or in the engine compartment.

Q8: Can a bad battery cause the Eco Start Stop to not work?

A: Yes, a low or failing battery is one of the most common reasons for the system to malfunction.

Q9: Is it worth fixing the Eco Start Stop system?

A: Yes, a properly functioning system improves fuel efficiency and reduces emissions.

Q10: What diagnostic tools do I need to troubleshoot the Eco Start Stop system?

A: A car battery tester, OBD-II scanner, and multimeter are essential tools for troubleshooting the system.