U2791 – Lost Communication with the Hybrid Powertrain Control Module (HPCM) A.

The ODBII code U2791 indicates a loss of communication with the Hybrid Powertrain Control Module (HPCM) A, which may affect the vehicle’s hybrid system functionality.

The severity of ODBII code U2791 is typically considered moderate to severe.

Common Causes For: U2790 U2790: Control Module Communication Bus Fault

• Faulty Hybrid Powertrain Control Module (HPCM)
• Damaged or corroded wiring or connectors
• Poor ground connections
• Communication network issues (e.g., CAN bus problems)
• Blown fuses
• Software or firmware issues
• Battery or power supply problems

Common misdiagnosis for U2791 Lost Communication with the Hybrid Powertrain Control Module (HPCM) A.

• Faulty wiring or connectors
• Defective Hybrid Powertrain Control Module (HPCM)
• Issues with the Engine Control Module (ECM)
• Battery or power supply problems
• Faulty sensors related to the hybrid system
• Communication issues with other control modules
• Software or firmware issues in the HPCM or ECM

Common Troubleshooting Steps

When dealing with the OBD-II code U2791, which indicates “Lost Communication with the Hybrid Powertrain Control Module (HPCM) A,” 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. This can provide more context and help identify related issues.
• Inspect the Wiring and Connectors: **Visual Inspection: Check the wiring harness and connectors related to the HPCM for any signs of damage, corrosion, or loose connections.
• **Connector Pins: Ensure that the pins in the connectors are not bent, corroded, or damaged.
• Check Power and Ground: **Power Supply: Verify that the HPCM 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 HPCM are secure and free of corrosion.
• Inspect the HPCM: If accessible, check the HPCM for any physical damage or signs of overheating.
• Ensure that the module is properly mounted and that there are no loose screws or bolts.
• Check Communication Lines: **CAN Bus Communication: Since the HPCM communicates over the CAN bus, check the integrity of the CAN bus wiring. Look for shorts, opens, or high resistance in the communication lines.
• **Termination Resistors: Ensure that the CAN bus has the proper termination resistors in place.
• Test the HPCM: If all wiring and connections appear to be in good condition, you may need to test the HPCM itself. This can often require specialized diagnostic equipment or tools.
• If possible, swap the HPCM with a known good unit to see if the issue persists.
• Check for Software Updates: Sometimes, communication issues can be resolved with a software update. Check with the manufacturer for any available updates for the HPCM.
• Clear Codes and Test Drive: After performing the above checks and repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns.
• Consult Technical Service Bulletins (TSBs): Look for any TSBs related to the HPCM or communication issues for your specific vehicle make and model. Manufacturers may have specific fixes or recommendations.
• Seek Professional Help: If you are unable to resolve the issue after these steps, it may be necessary to consult a professional mechanic or dealership with experience in hybrid vehicles and their control systems. By following these steps, you should be able to identify the root cause of the U2791 code and take appropriate action to resolve the communication issue with the Hybrid Powertrain Control Module.