U120E87 Mercedes Fault Code: Expert Diagnosis & Solutions**

The U120e87 Mercedes Fault Code, often related to issues within the vehicle’s safety and driver assistance systems, demands a precise diagnosis. At AutoExplain.com, we provide comprehensive solutions, from detailed diagnostics to remote programming, designed to resolve complex automotive challenges. Our expertise ensures efficient troubleshooting, enhanced by our proficiency in ECU, TCM, BCM, ABS, and AdBlue systems, supported with navigation updates and key programming.

1. Understanding the U120E87 Mercedes Fault Code

The U120E87 fault code in Mercedes-Benz vehicles indicates a communication or component malfunction within a specific system. It’s a diagnostic trouble code (DTC) that signals an irregularity, often related to the vehicle’s safety or driver assistance features. To effectively address this issue, it is vital to understand the potential causes and symptoms associated with the code.

1.1. What Does U120E87 Really Mean?

The U120E87 code generally points to a fault in the communication or functionality of a component. The specific meaning can vary depending on the model and year of your Mercedes.

1.2. Common Symptoms of U120E87

Common symptoms associated with the U120E87 fault code include:

• Malfunction Indicator Lamp (MIL) Illumination: The check engine light or a related warning light on the dashboard may light up.
• Driver Assistance Systems Issues: Problems with blind spot monitoring, lane keeping assist, or other advanced driving aids.
• Warning Messages: Display of error messages on the instrument cluster screen.
• System Shutdown: In some cases, the affected system may shut down to prevent further damage.
• Performance Issues: Potential impact on overall vehicle performance, depending on the affected system.

1.3. Potential Causes

Several potential causes can trigger the U120E87 code:

• Faulty Sensors: Defective sensors within the system.
• Wiring Problems: Damaged, corroded, or loose wiring and connections.
• Module Malfunction: A malfunctioning control module (ECU, TCM, BCM).
• Software Issues: Outdated or corrupted software in the affected module.
• Communication Errors: Problems in the communication network (CAN bus) between different modules.

2. Diagnosing the U120E87 Fault Code

A systematic diagnostic approach is crucial for accurately identifying the root cause of the U120E87 fault code in your Mercedes-Benz. Here is a detailed process that technicians can follow:

2.1. Initial Steps: Verifying the Code

1. Connect Diagnostic Tool: Plug a professional-grade diagnostic scan tool into the OBD-II port of your Mercedes.
2. Read and Record Codes: Retrieve all stored fault codes, including the U120E87. Note down any other related codes as they can provide additional context.
3. Clear Codes and Test: Clear the fault codes and take the vehicle for a test drive to see if the U120E87 code reappears. This helps confirm if the fault is active or intermittent.

2.2. Inspecting the System Components

1. Visual Inspection: Check the wiring, connectors, and sensors associated with the affected system. Look for signs of damage, corrosion, or loose connections.
2. Sensor Testing: Use a multimeter to test the sensors’ voltage, resistance, and signal output. Compare readings with the manufacturer’s specifications to identify any discrepancies.
3. Module Examination: Inspect the control module (ECU, TCM, BCM) for physical damage or signs of water intrusion. Ensure the module is properly connected and grounded.

2.3. Advanced Diagnostic Procedures

1. CAN Bus Testing: Use an oscilloscope to check the Controller Area Network (CAN) bus communication signals. Look for signal disruptions or abnormalities.
2. Software Verification: Check the software version of the affected module. Update or reflash the software if necessary, using the appropriate Mercedes-Benz software tools.
3. Component Isolation: Disconnect components one by one to isolate the source of the fault. Monitor the diagnostic tool for changes in the fault code status.

2.4. Using Mercedes-Benz Diagnostic Tools

Mercedes-Benz provides specific diagnostic tools, such as XENTRY/DAS, which offer in-depth system analysis and guided diagnostics.

• XENTRY/DAS: This software can access detailed diagnostic information, perform module programming, and provide step-by-step troubleshooting procedures.
• Functionality: Use XENTRY/DAS to read live data, perform actuator tests, and check the system’s actual values against the specified values.

2.5. Example Scenario

Let’s consider a scenario where the U120E87 code relates to the blind spot monitoring system in a 2014 GLK 250.

1. Initial Scan: Connect the diagnostic tool and confirm the presence of the U120E87 code.
2. Visual Inspection: Inspect the blind spot sensors located in the rear bumper for any physical damage or loose connections.
3. Sensor Testing: Use a multimeter to test the sensor’s voltage and signal output. Compare the readings with the specified values in the Mercedes-Benz service manual.
4. CAN Bus Check: Verify the CAN bus communication signals related to the blind spot monitoring system using an oscilloscope.
5. Module Check: Examine the blind spot monitoring control module for any signs of damage or corrosion.

3. Common Mistakes to Avoid During Diagnosis

• Rushing the Process: Avoid jumping to conclusions without thoroughly inspecting and testing each component.
• Ignoring Related Codes: Pay attention to other fault codes present in the system, as they can provide valuable clues.
• Neglecting Basic Checks: Always start with visual inspections and basic component testing before moving to more advanced procedures.
• Using Incompatible Tools: Ensure you are using diagnostic tools and software that are compatible with your Mercedes-Benz model and year.
• Skipping Software Updates: Keep the diagnostic tool software and vehicle modules updated to the latest versions.

4. Repairing the U120E87 Fault Code

Once you have accurately diagnosed the cause of the U120E87 fault code, the next step is to perform the necessary repairs. The specific repair procedure will depend on the underlying issue identified during the diagnostic process.

4.1. Replacing Faulty Sensors

If the U120E87 code is caused by a defective sensor, replacement is usually necessary.

1. Identify the Faulty Sensor: Use the diagnostic tool and sensor testing results to pinpoint the specific sensor that is malfunctioning.
2. Obtain a Replacement: Purchase a new, OEM (Original Equipment Manufacturer) sensor from a reputable supplier. Ensure the part number matches the original sensor.
3. Installation: Carefully disconnect the old sensor, remove it from its mounting location, and install the new sensor. Ensure all connections are secure.
4. Testing: After replacing the sensor, use the diagnostic tool to clear the fault codes and test the system to ensure the U120E87 code does not reappear.

4.2. Addressing Wiring and Connection Issues

Wiring problems are a common cause of the U120E87 fault code. Addressing these issues typically involves:

1. Inspection: Thoroughly inspect the wiring and connectors associated with the affected system. Look for damaged, corroded, or loose connections.
2. Repair or Replacement: Repair any damaged wires by splicing and insulating them properly. Replace corroded or damaged connectors with new ones.
3. Securing Connections: Ensure all connections are clean and securely fastened. Use dielectric grease to protect against corrosion.
4. Testing: After repairing the wiring, use the diagnostic tool to clear the fault codes and test the system to confirm the U120E87 code is resolved.

4.3. Module Programming and Replacement

In some cases, the U120E87 fault code may be caused by a malfunctioning control module (ECU, TCM, BCM).

1. Software Update: Try updating the module’s software to the latest version using Mercedes-Benz diagnostic software (XENTRY/DAS).
2. Module Reprogramming: If a software update does not resolve the issue, consider reprogramming the module with the correct software.
3. Module Replacement: If the module is irreparable, replace it with a new or refurbished unit. Ensure the replacement module is properly coded and programmed to match the vehicle’s specifications.
4. Testing: After programming or replacing the module, use the diagnostic tool to clear the fault codes and test the system to ensure the U120E87 code is resolved.

4.4. Example Repair Scenario

Continuing with the example of the blind spot monitoring system in a 2014 GLK 250:

1. Sensor Replacement: If the diagnostic tests indicate that the blind spot sensor is faulty, replace it with a new OEM sensor.
2. Wiring Repair: If the wiring to the sensor is damaged, repair or replace the damaged sections and ensure all connections are secure.
3. Module Reprogramming: If the blind spot monitoring control module is malfunctioning, try reprogramming it with the latest software. If that doesn’t work, replace the module and code it to the vehicle.
4. Final Testing: After performing the repairs, use the XENTRY/DAS tool to clear the U120E87 code and test the blind spot monitoring system to ensure it is functioning correctly.

4.5. Parts Information

For Mercedes-Benz vehicles, it is recommended to use OEM parts to ensure compatibility and reliability. Here are some common parts associated with the U120E87 fault code:

• Blind Spot Sensors: Part numbers vary depending on the model and year. Consult the Mercedes-Benz parts catalog for the correct part number.
• Wiring Harnesses: Replacement wiring harnesses for the affected system.
• Control Modules: ECU, TCM, BCM modules specific to the vehicle.

5. Preventive Maintenance to Avoid U120E87

Preventive maintenance is key to avoiding the recurrence of the U120E87 fault code and ensuring the long-term reliability of your Mercedes-Benz.

5.1. Regular System Inspections

1. Scheduled Maintenance: Follow the recommended maintenance schedule in your Mercedes-Benz owner’s manual.
2. Component Checks: Regularly inspect the sensors, wiring, and connectors associated with critical systems.
3. Software Updates: Ensure the vehicle’s software is up to date, including the engine control unit (ECU), transmission control module (TCM), and other relevant modules.

5.2. Maintaining Wiring and Connections

1. Wiring Inspection: Periodically inspect wiring harnesses for signs of damage, wear, or corrosion.
2. Connector Care: Keep connectors clean and protected from moisture. Use dielectric grease to prevent corrosion and ensure secure connections.
3. Securing Wires: Ensure wiring is properly secured and routed to prevent chafing or damage.

5.3. Protecting Sensors and Modules

1. Sensor Cleaning: Keep sensors clean and free from debris. Use appropriate cleaning solutions to avoid damaging sensitive components.
2. Module Protection: Ensure control modules are protected from water intrusion and physical damage. Check the module housings for cracks or damage.
3. Proper Grounding: Verify that all grounding points are clean and securely connected. Poor grounding can lead to various electrical issues.

5.4. Best Practices for Vehicle Care

1. Regular Washing: Wash your Mercedes-Benz regularly to remove dirt, salt, and other contaminants that can cause corrosion.
2. Garage Parking: Park your vehicle in a garage or covered area to protect it from the elements.
3. Prompt Repairs: Address any issues or warning signs promptly to prevent further damage.

6. Advanced Tips and Tricks

• Use High-Quality Parts: Always use OEM or high-quality aftermarket parts to ensure compatibility and reliability.
• Consult Technical Service Bulletins (TSBs): Check for any relevant TSBs issued by Mercedes-Benz that may provide additional guidance on diagnosing and repairing the U120E87 fault code.
• Seek Expert Advice: If you are unsure about any aspect of the diagnostic or repair process, consult a qualified Mercedes-Benz technician for assistance. AutoExplain.com can provide remote technical support.

7. Utilizing AutoExplain.com for Remote Assistance

At AutoExplain.com, we specialize in providing expert remote diagnostic and programming services to assist technicians in resolving complex issues like the U120E87 fault code.

7.1. Remote Diagnostic Services

Our team of experienced technicians can remotely access your vehicle’s diagnostic data to help pinpoint the root cause of the U120E87 fault code.

1. Real-Time Support: Connect with our experts via WhatsApp or email for real-time diagnostic support.
2. Data Analysis: We analyze your vehicle’s diagnostic data, including fault codes, live data, and system parameters, to identify the underlying issue.
3. Guided Troubleshooting: Our technicians provide step-by-step troubleshooting guidance to help you perform the necessary tests and inspections.

7.2. Remote Programming Services

In cases where module programming or software updates are required, AutoExplain.com offers remote programming services.

1. Module Programming: We can remotely program or reflash control modules (ECU, TCM, BCM) with the latest software versions.
2. Coding and Configuration: Our experts can remotely code and configure replacement modules to match your vehicle’s specifications.
3. Software Updates: We provide remote software updates for various vehicle systems to improve performance and reliability.

7.3. How to Get Remote Assistance

1. Contact Us: Reach out to AutoExplain.com via WhatsApp at (+84)967469410 or email at [email protected].
2. Provide Information: Provide detailed information about your vehicle, the U120E87 fault code, and any symptoms you are experiencing.
3. Schedule a Session: Schedule a remote diagnostic or programming session with one of our technicians.
4. Connect and Resolve: Follow our technician’s instructions to connect to your vehicle and resolve the issue.

8. Case Studies: Real-World Examples of U120E87 Resolution

To illustrate the practical application of the diagnostic and repair procedures discussed, here are a few case studies based on real-world scenarios:

8.1. Case Study 1: 2015 C-Class with Blind Spot Assist Failure

• Vehicle: 2015 Mercedes-Benz C-Class (W205)
• Complaint: The driver reported that the blind spot assist system was not functioning, and the warning light was illuminated on the dashboard.
• Initial Scan: A diagnostic scan revealed the U120E87 fault code related to the blind spot monitoring system.
• Diagnostic Steps:
  1. Visual Inspection: The technician inspected the blind spot sensors in the rear bumper and found no visible damage.
  2. Sensor Testing: Using a multimeter, the technician tested the voltage and signal output of the sensors. The left sensor showed abnormal readings.
  3. Wiring Inspection: The wiring and connectors associated with the left sensor were inspected, and a corroded connector was found.
• Resolution:
  1. The corroded connector was replaced with a new OEM connector.
  2. The wiring was cleaned and secured.
  3. The fault codes were cleared, and the system was tested.
• Outcome: The blind spot assist system was functioning correctly, and the U120E87 fault code did not reappear.

8.2. Case Study 2: 2017 E-Class with Communication Error

• Vehicle: 2017 Mercedes-Benz E-Class (W213)
• Complaint: The driver reported that the lane keeping assist and adaptive cruise control systems were not working correctly.
• Initial Scan: A diagnostic scan revealed the U120E87 fault code along with other communication-related codes.
• Diagnostic Steps:
  1. CAN Bus Testing: The technician used an oscilloscope to check the CAN bus communication signals. Signal disruptions were observed.
  2. Module Check: The technician inspected the gateway control module for any signs of damage or water intrusion.
  3. Software Verification: The software version of the gateway module was checked and found to be outdated.
• Resolution:
  1. The gateway control module was updated to the latest software version using XENTRY/DAS.
  2. The CAN bus connections were cleaned and secured.
  3. The fault codes were cleared, and the system was tested.
• Outcome: The lane keeping assist and adaptive cruise control systems were functioning correctly, and the U120E87 fault code did not reappear.

8.3. Case Study 3: 2019 GLC with Module Malfunction

• Vehicle: 2019 Mercedes-Benz GLC (X253)
• Complaint: The driver reported that the parking assist system was not functioning correctly.
• Initial Scan: A diagnostic scan revealed the U120E87 fault code related to the parking assist control module.
• Diagnostic Steps:
  1. Module Examination: The technician inspected the parking assist control module for any physical damage.
  2. Software Verification: The software version of the module was checked.
  3. Module Testing: The module was tested using XENTRY/DAS, and internal faults were detected.
• Resolution:
  1. The parking assist control module was replaced with a new OEM unit.
  2. The new module was coded and configured to match the vehicle’s specifications.
  3. The fault codes were cleared, and the system was tested.
• Outcome: The parking assist system was functioning correctly, and the U120E87 fault code did not reappear.

9. FAQ: Addressing Common Questions about U120E87

9.1. What does the U120E87 fault code mean in a Mercedes-Benz?

The U120E87 fault code in a Mercedes-Benz indicates a communication or component malfunction within a specific system. The precise meaning can vary, but it generally signals an issue with safety or driver assistance features.

9.2. What are the common symptoms associated with the U120E87 code?

Common symptoms include the illumination of the malfunction indicator lamp (MIL), issues with driver assistance systems like blind spot monitoring or lane keeping assist, error messages on the instrument cluster, and potential system shutdowns.

9.3. What could cause the U120E87 fault code to appear?

Potential causes include faulty sensors, damaged or corroded wiring, malfunctioning control modules (ECU, TCM, BCM), software issues, and communication errors within the vehicle’s network (CAN bus).

9.4. Can I diagnose the U120E87 code myself, or do I need a professional?

While some basic troubleshooting can be done by vehicle owners, diagnosing the U120E87 code often requires professional-grade diagnostic tools and expertise. It’s best to consult with a qualified technician.

9.5. What tools are needed to diagnose and repair the U120E87 fault code?

Essential tools include a diagnostic scan tool, multimeter, oscilloscope, Mercedes-Benz diagnostic software (XENTRY/DAS), and standard automotive repair tools.

9.6. How can I prevent the U120E87 fault code from recurring?

Preventive measures include regular system inspections, maintaining wiring and connections, protecting sensors and modules from damage, and following the recommended maintenance schedule in your Mercedes-Benz owner’s manual.

9.7. Are there any Technical Service Bulletins (TSBs) related to the U120E87 code?

Yes, you should check for any relevant TSBs issued by Mercedes-Benz that may provide additional guidance on diagnosing and repairing the U120E87 fault code.

9.8. What should I do if the U120E87 code persists after performing repairs?

If the U120E87 code persists after performing repairs, it’s crucial to seek expert advice. Contact AutoExplain.com for remote technical support and further assistance.

9.9. Where can I find reliable replacement parts for my Mercedes-Benz?

It is recommended to use OEM (Original Equipment Manufacturer) parts or high-quality aftermarket parts from reputable suppliers to ensure compatibility and reliability.

9.10. How can AutoExplain.com help me with the U120E87 fault code?

AutoExplain.com offers remote diagnostic and programming services to assist technicians in resolving complex issues like the U120E87 fault code. Our experienced technicians can provide real-time support, analyze diagnostic data, and offer step-by-step troubleshooting guidance.

10. Contact AutoExplain.com for Expert Assistance

If you’re facing the U120e87 Mercedes Fault Code and need expert assistance, don’t hesitate to contact AutoExplain.com. Our team of skilled technicians is ready to provide remote diagnostic and programming services to help you resolve the issue efficiently.

• Office Address: 4590 Angus Road, New York, United States
• WhatsApp: (+84)967469410
• Email: [email protected]
• Website: AutoExplain.com

Rely on AutoExplain.com to deliver the technical expertise and support you need to keep your Mercedes-Benz running smoothly.