A faulty DC/DC converter control module B, often due to internal failure from heat or voltage spikes; Damaged, corroded, or loose wiring or connectors in the CAN bus circuit between the converter module and the primary control module; A blown fuse or poor ground connection supplying power or ground to the converter module; Low or unstable 12-volt battery voltage causing the converter module to shut down or reset; A software glitch or outdated calibration in the converter module or primary control module; CAN bus network faults such as a shorted or open data line affecting communication; Water intrusion or physical damage to the converter module or its harness

DTC codes / U02xx · Lost communication with a control module / U0299

U0299Lost Communication With DC/DC Converter Control Module B

Q: What does code U0299 mean?

Lost Communication With DC/DC Converter Control Module B. U0299 is a generic network communication code indicating that the primary control module has lost contact with the DC/DC converter control module B, which is responsible for converting high-voltage battery power to low-voltage power for the vehicle's accessories. The computer detects this when it stops receiving the periodic controller area network (CAN) messages that the converter module normally broadcasts.

U0299 is a generic network communication code indicating that the primary control module has lost contact with the DC/DC converter control module B, which is responsible for converting high-voltage battery power to low-voltage power for the vehicle's accessories. The computer detects this when it stops receiving the periodic controller area network (CAN) messages that the converter module normally broadcasts.

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 service vehicle soon message
Often no symptoms besides the warning light, especially if the low-voltage system is still being charged
A low-voltage battery that drains quickly or fails to hold a charge
Electrical accessories such as lights, infotainment, or power windows operating intermittently or dimming
Reduced power or limited operation in hybrid and electric vehicles as the system enters a fail-safe mode
Multiple unrelated warning lights or communication codes stored in other modules

Common causes, most likely first

A faulty DC/DC converter control module B, often due to internal failure from heat or voltage spikes
Damaged, corroded, or loose wiring or connectors in the CAN bus circuit between the converter module and the primary control module
A blown fuse or poor ground connection supplying power or ground to the converter module
Low or unstable 12-volt battery voltage causing the converter module to shut down or reset
A software glitch or outdated calibration in the converter module or primary control module
CAN bus network faults such as a shorted or open data line affecting communication
Water intrusion or physical damage to the converter module or its harness

How to diagnose and fix it

Perform a full scan of all modules to confirm U0299 is current and check for related communication codes
Inspect the 12-volt battery state of charge and perform a load test; recharge or replace if weak
Check all fuses and relays that supply power to the DC/DC converter control module B
Visually inspect the converter module connectors and harness for corrosion, chafing, or loose pins; repair as needed
Measure CAN bus voltage and resistance at the converter module connector to verify communication lines are intact
If wiring and power are good, substitute a known-good converter module or perform a module reprogramming per manufacturer procedure
Clear codes and perform a road test to verify communication is restored and no codes return

Don't Replace the Converter Before These Checks

A weak or failing 12-volt battery is a frequent culprit behind U0299 because the converter module may not initialize properly at low voltage, so always load-test the battery first.
Corroded or loose ground connections on the converter module can mimic an internal module failure, and cleaning them often resolves the code without parts replacement.
On some vehicles, U0299 sets after jump-starting or battery replacement due to voltage spikes, and a simple code clear and relearn procedure may be all that is needed.
The code can be stored alongside other communication codes like U0100 or U0298, so diagnosing the root cause requires checking all modules rather than focusing only on the converter.
A failed DC/DC converter may still allow the vehicle to run on the 12-volt battery alone for a short time, so the absence of immediate symptoms does not mean the fault is harmless.

Can I keep driving with U0299?

You can usually drive the vehicle short distances to a repair shop, but avoid long trips or heavy electrical loads because the 12-volt battery may not be charged and the vehicle could stall or enter a reduced-power mode. If multiple warning lights appear or the battery drains quickly, stop driving and seek professional diagnosis.

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.