A weak or failing 12-volt battery causing low system voltage and communication dropouts; Corroded, loose, or damaged wiring and connectors on the module's power, ground, or network circuits; A faulty Battery Charger Control Module B itself, including internal failure or water intrusion; A shorted or open data bus wire (CAN, LIN, or dedicated serial line) between the module and the network; Poor grounds shared with the charging system or body control circuits; Aftermarket accessories or improper repairs that disturbed the module's wiring or network; A software or configuration issue in the module or the module that set the code

DTC codes / U01xx · Lost communication with a control module / U01BB

U01BBLost Communication With Battery Charger Control Module B

Q: What does code U01BB mean?

Lost Communication With Battery Charger Control Module B. U01BB is a generic network communication code indicating that one control module on the vehicle's data bus has stopped receiving messages from the Battery Charger Control Module B. The computer that set the code detected a loss of the periodic heartbeat or message from that specific module, not necessarily a charging system failure itself.

U01BB is a generic network communication code indicating that one control module on the vehicle's data bus has stopped receiving messages from the Battery Charger Control Module B. The computer that set the code detected a loss of the periodic heartbeat or message from that specific module, not necessarily a charging system failure itself.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaLost communication with a control module

Symptoms you may notice

Illumination of the check engine light or service vehicle soon message
Often no symptoms besides the warning light, with the vehicle charging and driving normally
A charging system warning lamp or message on the instrument cluster
Reduced or disabled high-voltage charging on plug-in hybrid and electric vehicles
Other unrelated warning lights or module communication codes appearing at the same time
Intermittent electrical accessories or starting issues if the module shares a power or ground circuit

Common causes, most likely first

A weak or failing 12-volt battery causing low system voltage and communication dropouts
Corroded, loose, or damaged wiring and connectors on the module's power, ground, or network circuits
A faulty Battery Charger Control Module B itself, including internal failure or water intrusion
A shorted or open data bus wire (CAN, LIN, or dedicated serial line) between the module and the network
Poor grounds shared with the charging system or body control circuits
Aftermarket accessories or improper repairs that disturbed the module's wiring or network
A software or configuration issue in the module or the module that set the code

How to diagnose and fix it

Verify the 12-volt battery state of charge and perform a load test, charging or replacing it as needed
Inspect and clean the Battery Charger Control Module B connectors and its power and ground connections
Check fuses and relays that supply the module and confirm voltage and ground at the module with a multimeter
Use a scan tool to read all module codes and check for other U-codes that point to a shared bus fault
Perform a voltage drop test on the module's ground and power circuits under load
Scope or measure the data bus at the module to confirm the network is intact and the module is responding
If wiring and power are good, test or replace the Battery Charger Control Module B and verify communication returns

Why the charger module goes silent

A weak 12-volt battery is the most common cause of this code on vehicles that sit or are driven short distances, because low voltage drops network messages before any module actually fails.
The code does not always mean the charger module is bad; a single corroded ground or a chafed bus wire can take the module offline while the module itself is healthy.
On plug-in hybrids and electric vehicles, this code can disable high-voltage charging entirely, so the vehicle may start and run on the engine but refuse to accept a charge.
Aftermarket alarms, remote starters, or dash camera wiring tapped into the wrong circuit can disturb the module's network and set U01BB intermittently.
Other U-codes stored alongside U01BB often reveal whether the fault is isolated to this module or part of a wider bus problem, so read every module before replacing parts.

Can I keep driving with U01BB?

The vehicle is usually safe to drive if it starts and runs normally, but on a plug-in hybrid or electric vehicle avoid relying on charging until the fault is repaired. Do not ignore repeated charging system warnings, and have the circuit tested before replacing the module.

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.