Loose, corroded, or damaged connector at the battery management control module; Broken, chafed, or shorted wire in the communication network between the module and the rest of the vehicle; Failed battery management control module, often due to internal circuit damage or water intrusion; Low or unstable 12-volt supply or a poor ground to the module, causing it to drop offline; Communication network fault such as a shorted data line or a failed network gateway; Aftermarket accessories or improper previous repairs disturbing the module's wiring

DTC codes / U01xx · Lost communication with a control module / U01BF

U01BFLost Communication with Battery Management Control Module

Q: What does code U01BF mean?

Lost Communication with Battery Management Control Module. U01BF means the vehicle's main computers have lost contact with the Battery Management Control Module over the high-speed communication network. The module that watches over the high-voltage battery pack has stopped reporting its voltage, temperature, and state-of-charge data, so other controllers set this code when the expected messages fail to arrive.

U01BF means the vehicle's main computers have lost contact with the Battery Management Control Module over the high-speed communication network. The module that watches over the high-voltage battery pack has stopped reporting its voltage, temperature, and state-of-charge data, so other controllers set this code when the expected messages fail to arrive.

SystemNetwork

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaLost communication with a control module

Symptoms you may notice

Illuminated check engine light or service vehicle soon message on the dash
Often no symptoms besides the warning light when the fault is intermittent
High-voltage battery gauge showing dashes, zero, or an implausible value
Vehicle refusing to enter Ready mode or start, especially on hybrid and electric models
Reduced power, limp-home mode, or a message to service the high-voltage system
Charging system warning or the car failing to accept a charge

Common causes, most likely first

Loose, corroded, or damaged connector at the battery management control module
Broken, chafed, or shorted wire in the communication network between the module and the rest of the vehicle
Failed battery management control module, often due to internal circuit damage or water intrusion
Low or unstable 12-volt supply or a poor ground to the module, causing it to drop offline
Communication network fault such as a shorted data line or a failed network gateway
Aftermarket accessories or improper previous repairs disturbing the module's wiring

How to diagnose and fix it

Scan all modules and record every stored code, then verify whether other modules can still communicate with the battery management control module
Inspect the module's connectors and harness for corrosion, pushed pins, chafing, and loose terminals, and check the 12-volt feed and ground at the module
Measure network resistance and voltage on the communication lines to rule out a short or open circuit before condemning the module
Check for technical service bulletins and software updates for the module and network gateway, since communication glitches are sometimes corrected by a reflash
If wiring and power are good, substitute a known-good module or perform a module communication test to confirm the module itself has failed
After repair, clear codes and drive the vehicle through a complete power cycle to confirm the module stays online and the code does not return

Why the battery module drops offline

A weak or failing 12-volt battery is a common hidden cause, because the battery management module may reset or drop off the network when supply voltage sags during cranking or load changes.
This code does not automatically mean the high-voltage battery pack is bad; the fault is in the module or its communication path, and replacing the pack on this code alone is an expensive misdiagnosis.
Water intrusion or corrosion at the module connector is frequently missed, especially on vehicles where the module is mounted low in the floor or near the battery pack.
A single failed module on the network can pull down communication for other modules, so always check whether additional communication codes are stored before focusing on the battery management module.
Aftermarket alarms, chargers, or dash cameras tapped into the wrong circuit can disturb the network and cause intermittent loss of communication that only appears under certain conditions.

Can I keep driving with U01BF?

Do not continue driving normally, because a vehicle that has lost battery management data may shut down, refuse to start, or fail to manage the high-voltage pack safely. Move the car to a safe location and have it diagnosed before driving further, especially if the dash shows a high-voltage or charging warning.

Tools that help

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