A discharged, weak, or failed 12-volt battery that drags down module supply voltage and disrupts bus communication.; Corroded, loose, or damaged connector terminals at the DC/DC converter or at the modules on the same bus segment.; A blown fuse or open circuit in the converter's power or ground feed, leaving the module unpowered and silent.; Wiring damage such as chafed or broken CAN high and CAN low conductors between the converter and the network.; A faulty DC/DC converter control module that has lost its internal communication interface.; A failed or intermittent module on the same bus segment that is corrupting or shorting the network.; Poor grounds shared between the converter, chassis, and body modules causing intermittent communication dropouts.

DTC codes / U01xx · Lost communication with a control module / U01BD

U01BDLost Communication With DC/DC Converter Control Module C

Q: What does code U01BD mean?

Lost Communication With DC/DC Converter Control Module C. U01BD is a generic communication fault indicating that one or more control modules have lost the CAN (Controller Area Network) data link with the DC/DC converter control module, which is the electronic unit that steps high-voltage battery power down to charge the 12-volt system on hybrid and electric vehicles. The detecting module has stopped receiving the periodic status messages it expects from the converter over the communication bus, so it flags the converter as missing rather than reporting a fault inside the converter itself.

U01BD is a generic communication fault indicating that one or more control modules have lost the CAN (Controller Area Network) data link with the DC/DC converter control module, which is the electronic unit that steps high-voltage battery power down to charge the 12-volt system on hybrid and electric vehicles. The detecting module has stopped receiving the periodic status messages it expects from the converter over the communication bus, so it flags the converter as missing rather than reporting a fault inside the converter itself.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaLost communication with a control module

Symptoms you may notice

The warning light or message for the high-voltage system or charging system illuminates on the dashboard.
The 12-volt battery may run down because the converter is no longer charging it, leading to a no-crank or slow-crank condition.
The vehicle may enter a reduced-power or limp mode, or refuse to start, when the converter is part of the start-up communication chain.
Other unrelated warning lights may appear because multiple modules share the same bus segment.
Often no symptoms besides the warning light, with the vehicle driving normally until the 12-volt battery depletes.

Common causes, most likely first

A discharged, weak, or failed 12-volt battery that drags down module supply voltage and disrupts bus communication.
Corroded, loose, or damaged connector terminals at the DC/DC converter or at the modules on the same bus segment.
A blown fuse or open circuit in the converter's power or ground feed, leaving the module unpowered and silent.
Wiring damage such as chafed or broken CAN high and CAN low conductors between the converter and the network.
A faulty DC/DC converter control module that has lost its internal communication interface.
A failed or intermittent module on the same bus segment that is corrupting or shorting the network.
Poor grounds shared between the converter, chassis, and body modules causing intermittent communication dropouts.

How to diagnose and fix it

Perform a full scan of all modules and record every stored code, then check the 12-volt battery state of charge and load-test it before anything else.
Inspect and clean the DC/DC converter connectors and the connectors of modules sharing its bus segment, looking for corrosion, pushed pins, or water intrusion.
Check the converter's fuses, power feeds, and grounds with a multimeter and verify battery voltage reaches the module with the key on.
Measure CAN high and CAN low voltages and resistance at the converter connector to confirm the bus is intact and not shorted or open.
Use a scan tool with live data to watch for the converter's status messages and confirm whether it wakes and communicates at all.
If communication is absent but power, ground, and bus wiring test good, substitute a known-good converter or perform a module swap test to confirm the fault.
After repair, clear all codes, perform a full drive cycle, and recheck that the converter remains online with no recurring U01BD.

Why the converter often is not the culprit

A weak or failing 12-volt battery is one of the most common triggers for this code because low supply voltage causes modules to drop off the bus before any hardware actually fails.
Technicians frequently replace the DC/DC converter only to find a corroded connector pin or a chafed CAN wire was interrupting communication the whole time.
This code does not prove the converter is defective; it only proves the detecting module stopped hearing from it, so the fault may live in the wiring, a shared ground, or another module on the same bus.
Water intrusion into the converter's connector or housing is a recurring cause on vehicles where the unit is mounted low in the engine bay or under the floor.
A single failed module on the same bus segment can pull the network down and cause U01BD alongside communication codes for several other modules.

Can I keep driving with U01BD?

You can usually drive a short distance to a repair shop, but avoid long trips and repeated starts because the 12-volt battery is not being charged and the vehicle may stall or fail to restart once it drains. If the vehicle is already in limp mode or showing a high-voltage warning, stop driving and arrange a tow.

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.