U2991 – Lost Communication with Vehicle Control Module.

The ODBII code U2991 indicates a loss of communication with the vehicle control module, suggesting that the module is not responding or is unable to communicate with other systems in the vehicle.

The severity of ODBII code U2991 is generally considered moderate to severe.

Common Causes For: U2990 Lost Communication with Vehicle Control Module.

• Faulty Vehicle Control Module (VCM)
• Damaged wiring or connectors
• Poor ground connections
• Corrupted software or firmware in the VCM
• Faulty communication network (CAN bus issues)
• Low battery voltage or power supply issues
• Intermittent electrical connections
• Other module failures affecting communication

Common misdiagnosis for U2991 Lost Communication with Vehicle Control Module.

• Faulty wiring or connectors
• Defective vehicle control module (VCM)
• Issues with the powertrain control module (PCM)
• Malfunctioning body control module (BCM)
• Problems with the engine control module (ECM)
• Faulty sensors or actuators
• Battery or charging system issues
• Software or firmware glitches
• Communication network problems (CAN bus issues)
• Grounding issues

Common Troubleshooting Steps

When dealing with the OBD-II code U2991, which indicates “Lost Communication with Vehicle Control Module,” there are several common troubleshooting steps you can follow to diagnose and potentially resolve the issue. Here’s a structured approach:

• Check for Additional Codes: Use an OBD-II scanner to check for any other trouble codes that may be present. Sometimes, multiple codes can provide more context for the issue.
• Inspect the Wiring and Connectors: **Visual Inspection: Look for damaged, frayed, or corroded wiring and connectors related to the Vehicle Control Module (VCM) and other modules.
• **Connector Integrity: Ensure that all connectors are securely attached and free of dirt or corrosion.
• Check Power and Ground: **Power Supply: Verify that the VCM is receiving the correct voltage. Use a multimeter to check the power supply to the module.
• **Ground Connections: Ensure that the ground connections for the VCM are secure and free of corrosion.
• Inspect the Vehicle Control Module: **Module Condition: Check for any signs of physical damage to the VCM itself.
• **Reprogramming: If applicable, consider reprogramming or updating the software of the VCM.
• Check for Communication Issues: **CAN Bus Integrity: Inspect the CAN bus wiring for shorts, opens, or other issues. Use a multimeter or oscilloscope to check for proper communication signals.
• **Module Communication: Use a scan tool to check if other modules in the vehicle can communicate with the VCM. If other modules are also unresponsive, it may indicate a broader communication issue.
• Perform a Hard Reset: Disconnect the vehicle’s battery for a few minutes to reset the system. Reconnect and see if the code reappears.
• Check for Environmental Factors: Ensure that there are no external factors affecting the VCM, such as water intrusion or excessive heat.
• Consult Technical Service Bulletins (TSBs): Look for any TSBs related to your vehicle make and model that might address known issues with the VCM or communication problems.
• Seek Professional Help: If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or technician who has experience with your specific vehicle make and model.
• Replace the Module (if necessary): If all other troubleshooting steps fail and the VCM is determined to be faulty, replacement of the module may be required.Conclusion Troubleshooting OBD-II code U2991 involves a systematic approach to identify and resolve communication issues with the Vehicle Control Module. Always ensure safety precautions are taken when working with vehicle electronics, and consult a professional if you are unsure about any steps.