Diagnosing your 1999 Mercedes Benz E320 can sometimes feel like navigating a complex maze. When the check engine light illuminates, or you suspect an underlying issue, your first instinct might be to reach for an OBD II scanner. However, encountering a “no communication” message can be frustrating and leave you wondering where to turn next. Choosing the right OBD II scanner and understanding potential communication barriers are crucial for effective vehicle diagnostics.
Understanding the OBD II System in Your 1999 Mercedes Benz E320
The On-Board Diagnostics II (OBD II) system is a standardized system in vehicles, including your 1999 Mercedes Benz E320, that provides access to crucial vehicle health information. This system is designed to monitor various engine and emission control components, alerting you to potential problems through diagnostic trouble codes (DTCs). An OBD II scanner acts as the key to unlocking this information, allowing you to read these codes and gain insights into your car’s condition. For a classic like the 1999 E320, effectively utilizing the OBD II system is invaluable for maintenance and repair, potentially saving you time and money compared to dealership-only diagnostics.
Common Causes of OBD II Scanner No Communication with Your Mercedes E320
When your OBD II scanner fails to communicate with your 1999 Mercedes Benz E320, several potential issues could be at play. Let’s explore the common culprits:
1. Blown Fuses: The First Point of Inspection
A frequent reason for a lack of communication is a simple blown fuse. The OBD II port, also known as the ALDL (Assembly Line Diagnostic Link) connector, receives power through specific fuses in your Mercedes Benz E320’s fuse box. If the fuse supplying power to this port is blown, the scanner won’t be able to power up or establish a connection with the vehicle’s computer system.
Actionable Step: Consult your Mercedes Benz E320 owner’s manual or a fuse box diagram to locate the fuses associated with the diagnostic system. Specifically, fuses 15 and 17 are often relevant for the OBD II system in Mercedes models of this era. Check these fuses for any signs of damage or a broken filament. Replace any blown fuses with the correct amperage rating.
2. Relay Problems: Investigating the Electrical Circuit
Relays are electromechanical switches that control electrical circuits. While less common than fuses, a faulty relay in the OBD II power circuit can also prevent scanner communication.
Actionable Step: Locate the relays related to the engine control unit (ECU) and diagnostic system in your 1999 E320. Refer to your vehicle’s repair manual or online resources for relay locations. You can test a relay by swapping it with an identical relay from a less critical system (like the horn relay) to see if communication is restored. Alternatively, you can use a multimeter to test the relay’s functionality as outlined in guides on automotive electrical systems.
3. ALDL Connector Corrosion or Damage: Physical Connection Issues
The ALDL connector itself can be a source of problems. Corrosion on the connector pins or physical damage to the connector can disrupt the electrical connection needed for the scanner to communicate.
Actionable Step: Visually inspect the OBD II connector under your dashboard for any signs of corrosion, bent pins, or damage. Use a terminal cleaner or electrical contact cleaner to carefully clean the pins in the connector. Ensure the connector is free from debris and that the pins are straight and making good contact.
4. Engine Control Unit (ECU) Malfunction: A More Serious Issue
The ECU, or engine control unit, is the central computer that manages your Mercedes Benz E320’s engine and related systems. While ECUs are generally robust, they can occasionally fail. If the ECU itself is malfunctioning or has a power supply issue, it won’t be able to communicate with an OBD II scanner.
Actionable Step: ECU issues are more complex to diagnose and often require professional expertise. However, before suspecting the ECU, ensure you have thoroughly checked fuses, relays, and connector issues. If all else fails, ECU testing or replacement might be necessary, which is typically best handled by a qualified mechanic specializing in Mercedes Benz vehicles.
5. Scanner Incompatibility: Choosing the Right Tool
Not all OBD II scanners are created equal. Some basic scanners might have compatibility issues with certain vehicle makes or models, particularly older European vehicles like the 1999 Mercedes Benz E320. Some scanners may lack the necessary protocols or software to properly interface with your specific vehicle’s computer system.
Actionable Step: Verify that your OBD II scanner explicitly states compatibility with European vehicles and Mercedes Benz models, ideally including models around the 1999 E320 year. If you’re unsure, try using a different OBD II scanner, preferably one known for its broader vehicle compatibility or specifically recommended for Mercedes Benz vehicles. Higher-end professional scanners often have better compatibility and diagnostic capabilities for European cars. As noted in the original forum, sometimes more advanced scanners are needed for older Mercedes models.
Step-by-Step Troubleshooting Guide for No Communication
Follow these steps in a logical order to diagnose and resolve the “no communication” issue with your OBD II scanner:
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Verify Check Engine Light Function: Turn your ignition key to the “ON” position (without starting the engine). The check engine light (CEL) should illuminate briefly. If the CEL does not light up at all, this could indicate a broader electrical issue affecting the ECU and diagnostic system, reinforcing the need to check fuses and relays.
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Check OBD II System Fuses: Locate and inspect fuses 15 and 17 (or consult your owner’s manual for the correct fuses) in your Mercedes Benz E320’s fuse box. Replace any blown fuses.
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Inspect the ALDL Connector: Examine the OBD II connector for corrosion, damage, and bent pins. Clean the connector pins with electrical contact cleaner if necessary.
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Test Relays: Identify and test the relays related to the ECU and diagnostic system. Swap relays with identical ones or use a multimeter to check their function.
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Test Your Scanner on Another Vehicle: To rule out a faulty scanner, try using your OBD II scanner on a different vehicle (preferably a different make and model if possible). If the scanner works on another car, the issue is likely with your Mercedes Benz E320 and not the scanner itself.
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Consider Scanner Compatibility: If possible, try a different OBD II scanner, especially one known for European vehicle compatibility. Borrow a scanner from a friend or auto parts store, or consider investing in a scanner with enhanced compatibility.
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ECU and Wiring Checks (Advanced): If all the above steps fail, and you are comfortable with automotive electrical diagnostics, you can perform pin-to-pin checks of the wiring between the OBD II connector and the ECU using wiring diagrams for your 1999 Mercedes Benz E320. This is a more advanced step and may require specialized tools and knowledge. As a last resort, ECU failure should be considered, but this is less frequent than simpler electrical issues.
Choosing the Right OBD II Scanner for Your Mercedes Benz E320 1999
Selecting the right OBD II scanner is essential for effective diagnostics, especially for a sophisticated vehicle like the 1999 Mercedes Benz E320. Consider these factors when choosing a scanner:
- Mercedes Benz Compatibility: Ensure the scanner explicitly lists compatibility with Mercedes Benz vehicles and ideally includes models from the late 1990s.
- Protocol Support: The scanner should support the OBD II protocols used by your 1999 E320. Most modern scanners support the necessary protocols, but it’s worth verifying.
- Features: Beyond basic code reading, consider scanners that offer features like live data streaming, freeze frame data, and enhanced diagnostics for European vehicles. These advanced features can be invaluable for in-depth troubleshooting.
- Ease of Use: Choose a scanner with a user-friendly interface and clear display for easy navigation and code interpretation.
By systematically troubleshooting the potential causes of “no communication” and selecting a compatible OBD II scanner, you can effectively diagnose your 1999 Mercedes Benz E320 and take the necessary steps to keep it running smoothly. Remember to consult repair manuals and seek professional help when dealing with complex electrical issues or ECU problems.
