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DTC codes / U01xx · Lost communication with a control module / U01AD

U01ADLost Communication With Hybrid/EV Battery Interface Control Module N

This code means the vehicle's main control module has stopped receiving regular data messages from the hybrid or electric vehicle battery interface control module designated as 'N'. The computer detected a loss of the periodic communication signal that module is supposed to broadcast over the vehicle's communication network.

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, with the vehicle driving normally
  • Reduced power or a forced limp-home mode in some vehicles
  • Failure of the high-voltage battery to accept or deliver charge
  • Inability to start or engage drive in severe cases
  • Other unrelated warning lights appearing due to shared network communication

Common causes, most likely first

  1. Damaged or chafed wiring in the communication network circuit between the interface module and the main controller
  2. Corroded, loose, or backed-out pins in the interface module connector
  3. Failed hybrid/EV battery interface control module itself
  4. Loss of power or ground to the interface module, including a blown fuse
  5. Internal fault in another module that disrupts the shared communication bus
  6. Software or calibration issue in the interface module or main controller
  7. Water intrusion or physical damage to the module or its harness

How to diagnose and fix it

  1. Verify the code with a scan tool and check for related communication codes across all modules
  2. Inspect the interface module's fuses and confirm battery voltage and ground at its connector
  3. Perform a visual inspection of the communication network wiring and connectors for damage or corrosion
  4. Measure resistance and continuity on the communication bus circuits to rule out opens or shorts
  5. Check for technical service bulletins or software updates for the interface module
  6. Substitute a known-good module or perform a wiggle test on the harness while monitoring live data
  7. Replace and reprogram the hybrid/EV battery interface control module if all other checks pass

What to check before replacing the battery module

  • A weak or failing 12-volt battery is a common hidden cause of communication codes because modules drop offline when supply voltage sags during cranking.
  • The code can be set by a fault in a completely different module that shares the same communication bus, so always scan all modules before condemning the battery interface module.
  • Water intrusion into the module connector or harness is frequently missed during visual inspections and can cause intermittent loss of communication.
  • After replacing the interface module, reprogramming and sometimes a security relearn are required, and skipping this step will leave the code present.
  • Intermittent faults often appear only during vibration or temperature extremes, so a wiggle test and freeze-frame data review are more reliable than a static check.

Can I keep driving with U01AD?

If the vehicle drives normally with only the warning light on, you can drive it to a repair shop, but avoid long trips and high-load driving. If the vehicle enters limp mode, refuses to start, or shows a high-voltage battery warning, stop driving and have it towed to avoid further damage.

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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