Blown fuse or fusible link in the converter's high-voltage supply circuit; Damaged or corroded wiring or connector at the outlet or converter; Failed DC/AC converter unit due to internal component failure; Open circuit in the control wire between the BCM and the converter; Poor ground connection for the converter or outlet; Short to voltage or ground in the outlet circuit; Water intrusion or physical damage to the outlet assembly

DTC codes / B01xx · Airbags, seats, doors, lights and comfort systems / B0129

B0129DC/AC Converter A High Voltage Power Outlet "C" Circuit/Open

B0129 indicates that the body control module (BCM) has detected an open circuit or high-voltage fault on the DC/AC converter's 'C' power outlet circuit, which is typically the household-style AC socket in the rear cargo area or center console. The computer monitors the converter's output and control circuit, and when the voltage exceeds the expected range or the circuit is open, it stores this code and disables the outlet.

SystemBody

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaAirbags, seats, doors, lights and comfort systems

Symptoms you may notice

The AC power outlet does not provide power to connected devices
A warning light or message on the dash indicating a power outlet fault
The outlet may work intermittently or only with certain devices
Often no symptoms besides the warning light, especially if the outlet is rarely used
Other power outlets in the vehicle may also be affected if they share the same converter
The converter may emit a humming or buzzing noise when the ignition is on

Common causes, most likely first

Blown fuse or fusible link in the converter's high-voltage supply circuit
Damaged or corroded wiring or connector at the outlet or converter
Failed DC/AC converter unit due to internal component failure
Open circuit in the control wire between the BCM and the converter
Poor ground connection for the converter or outlet
Short to voltage or ground in the outlet circuit
Water intrusion or physical damage to the outlet assembly

How to diagnose and fix it

Check the fuse and relay for the DC/AC converter circuit and replace if blown
Inspect the outlet and converter connectors for corrosion, loose pins, or damage
Measure voltage at the converter's input and output with a multimeter to verify power and ground
Perform a voltage drop test on the ground circuit to ensure a good connection
Check the control circuit between the BCM and converter for continuity and shorts
If all circuits test good, replace the DC/AC converter unit
Clear the code and verify the outlet operates correctly with a known-good device

What Most Techs Miss on B0129

A common oversight is assuming the converter itself is faulty when the real problem is a blown fuse in a secondary fuse box that owners do not know exists.
The code can be set by a faulty outlet assembly even if the converter tests good, because the outlet contains a switch or sensor that signals the BCM.
In some vehicles, the DC/AC converter only operates when the engine is running, so testing with the ignition on but engine off can lead to a false diagnosis.
Water leaks into the rear quarter panel or cargo area often corrode the converter's connectors, causing an open circuit that mimics a failed converter.
After replacing the converter, some vehicles require a BCM relearn or calibration procedure to recognize the new unit and clear the code permanently.

Can I keep driving with B0129?

The vehicle remains safe to drive because the fault only affects the accessory power outlet, but avoid using the outlet until repaired to prevent further electrical issues. If the outlet is needed for critical devices, have it checked promptly.

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.