Experiencing issues starting your 2009 Mercedes E350 and encountering a U110B error code? This can be a frustrating situation, especially when your car suddenly refuses to cooperate. You’re not alone, and understanding what this code means is the first step towards resolving the problem. This guide will break down the U110B code, potential causes, and troubleshooting steps to get your Mercedes back on the road.
The error code U110B in your 2009 Mercedes E350 typically points to an issue within the Transmission Control Unit (TCU) communication system. Specifically, it indicates a fault, often described as “Fault in CAN communication with control unit ‘transmission control’ or no CAN communication.” Essentially, your car’s computer is signaling that it’s lost or experiencing interrupted communication with the TCU.
Alongside U110B, you might also be seeing a U0100 code, which signifies “Lost Communication with ECM/PCM ‘A'”. This further complicates the issue, suggesting a broader communication breakdown within your vehicle’s network. The Engine Control Module (ECM) or Powertrain Control Module (PCM) is crucial for engine management, and losing communication here is a significant problem.
Several factors can trigger these codes and lead to a no-start condition in your Mercedes E350:
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Low Battery Voltage: A weak or failing battery is a common culprit in Mercedes-Benz electrical issues. Modern Mercedes vehicles are highly sensitive to voltage fluctuations. If your battery voltage dips too low, it can disrupt communication between control units, triggering fault codes like U110B and U0100. As you mentioned, your voltage was at 11.7V initially, which is quite low and could be a contributing factor. Even after charging to 12.6V, a battery that’s internally weak might still cause problems under load.
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Faulty Transmission Control Unit (TCU): The TCU itself could be malfunctioning. Internal failures within the TCU can prevent it from communicating properly with the car’s network, leading to the U110B code.
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Engine Control Module (ECM/PCM) Issues: Similarly, problems with the ECM/PCM could disrupt communication. While less common than battery or TCU issues, ECM/PCM faults are possible.
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Wiring and Connection Problems: Damaged wiring, loose connectors, or corrosion in the CAN bus network (the communication network within your car) can interrupt signals between the TCU, ECM/PCM, and other modules. This is especially relevant if your car has been sitting unused, as rodents or corrosion can affect wiring.
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Sensor Malfunctions: While less directly related to communication codes, faulty sensors, particularly those involved in engine or transmission management, can sometimes indirectly trigger communication errors if they cause the control units to misbehave or shut down communication to protect the system.
Troubleshooting Steps:
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Battery Check: While you’ve already charged the battery, it’s crucial to have it properly load tested. A battery test at a reputable auto parts store (like O’Reilly’s, as you mentioned) can confirm if it’s truly healthy and holding a charge under load. Also, inspect battery terminals and connections for corrosion and ensure they are clean and tight. A voltage reading of 12.2V with the car “on” (ignition in accessory or run position) is a bit low; ideally, it should be closer to 12.5-12.8V.
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OBD-II Scanner Re-scan: After clearing the codes, rescan to confirm U110B and U0100 are still present. Persistent codes indicate an ongoing issue.
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Check TCU and ECM/PCM Connections: Locate the TCU (usually in the passenger footwell or under the hood, consult your owner’s manual or online resources for the exact location on a 2009 E350) and the ECM/PCM (typically under the hood). Carefully inspect the connectors for any signs of damage, corrosion, or loose connections. Gently reseat the connectors to ensure a good connection. Note: Be sure to disconnect the negative battery terminal before disconnecting any control unit connectors to prevent electrical damage.
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Inspect Wiring: Visually inspect the wiring harnesses leading to the TCU and ECM/PCM for any signs of damage, rodent activity, or wear. Pay close attention to areas where wiring might be exposed or routed near moving parts or heat sources.
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Professional Diagnosis: Given the complexity of Mercedes-Benz electrical systems, and the presence of communication fault codes, it’s highly recommended to seek professional diagnosis from a qualified mechanic specializing in Mercedes-Benz vehicles or a Mercedes-Benz dealership. They have specialized diagnostic tools (like Mercedes-Benz Star Diagnosis) that can pinpoint the exact cause of the U110B and U0100 codes and perform more in-depth troubleshooting, including CAN bus testing and control unit diagnostics.
While a low battery is a likely starting point, the U110B and U0100 codes suggest a deeper electrical or communication network problem. Don’t hesitate to seek professional help to accurately diagnose and repair your 2009 Mercedes E350 and get it running reliably again.
