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DTC codes / U01xx · Lost communication with a control module / U01A2

U01A2Lost Communication With Hybrid/EV Battery Interface Control Module C

U01A2 is a generic network communication code indicating that a control module on the vehicle's Controller Area Network (CAN) bus has lost contact with the Hybrid/EV Battery Interface Control Module C. The computer detected that expected periodic messages from this module stopped arriving within a defined time window, which sets the code and typically illuminates the warning light.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaLost communication with a control module

Symptoms you may notice

  • Illumination of the check engine light or a dedicated hybrid system warning light
  • Often no symptoms besides the warning light, especially if the fault is intermittent
  • Reduced hybrid or electric driving range, or the vehicle refusing to enter EV mode
  • A message on the dash such as 'Hybrid System Fault' or 'Service Vehicle Soon'
  • The vehicle may fail to start or may enter a limp-home mode if the battery interface module is critical to operation
  • Inconsistent charging behavior or the high-voltage battery gauge showing erratic readings

Common causes, most likely first

  1. A loose, corroded, or damaged electrical connector at the Hybrid/EV Battery Interface Control Module C
  2. Wiring damage (open, short, or chafed harness) in the CAN bus circuit between the interface module and the rest of the network
  3. A faulty Hybrid/EV Battery Interface Control Module C itself, such as internal failure or water intrusion
  4. Low or unstable 12-volt battery voltage causing network communication dropouts
  5. A poor ground connection for the interface module or the harness it shares
  6. CAN bus termination resistor failure or another module on the same bus segment disrupting communication
  7. Aftermarket accessories or improper previous repairs that disturbed the network wiring

How to diagnose and fix it

  1. Verify battery voltage and condition; charge or replace the 12-volt battery if it is below specification
  2. Inspect and reseat all connectors at the Hybrid/EV Battery Interface Control Module C, looking for corrosion, bent pins, or loose terminals
  3. Perform a visual inspection of the CAN bus wiring harness for chafing, pinches, or damage, especially near moving components and heat sources
  4. Use a scan tool to check for other communication codes and to confirm whether the module is completely offline or only intermittently missing
  5. Measure CAN bus resistance and voltage at the diagnostic connector to rule out bus-wide faults such as a shorted or open circuit
  6. If wiring and power/ground are good, substitute a known-good module or perform a module relearn/configuration as required by the manufacturer
  7. Clear the code and road-test the vehicle to confirm the repair, monitoring live data for the interface module's communication status

What a missing battery module message really means

  • A single lost communication code often points to a power or ground problem at the module rather than a failed module, so always check voltage and grounds before condemning the part.
  • Intermittent U01A2 codes are frequently caused by a loose connector that only loses contact during vibration or temperature swings, making a wiggle test essential.
  • The Hybrid/EV Battery Interface Control Module C may share a CAN segment with other high-voltage components, so a fault in a neighbouring module can mimic this code.
  • After a collision repair or battery service, a forgotten connector or a pinched harness is a common cause that technicians overlook when focusing on the module itself.
  • This code does not always mean the high-voltage battery is failing; it specifically indicates a communication loss, and the battery may be perfectly healthy.

Can I keep driving with U01A2?

If the vehicle drives normally and only the warning light is on, you can usually continue driving to a repair shop, but avoid long trips and heavy electrical loads. If the vehicle enters limp mode, refuses to start, or shows a high-voltage battery fault message, stop driving and have it towed to avoid further damage or safety risk.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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