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B0128

DC/AC Converter A High Voltage Power Outlet “B” Circuit/Open.

  • Generic
  • Body
  • Generic code
  • Low severity

How this code is built

B
SystemBody
0
Defined bySAE, the same on every car
1
AreaBody area 1
28
FaultThe specific fault in that area

What it means

B0128 is the SAE generic code for a circuit or open-circuit fault on power outlet 'B' fed by DC/AC converter A, the unit that turns high-voltage battery power into mains-style AC for sockets in the vehicle. The control unit saw an open circuit or a circuit reading outside the expected range between the converter and that outlet. Exact outlet locations and converter layout depend on the model, so check the manufacturer's data for the vehicle.

Symptoms

  • Mains-style power outlet B has no output
  • Outlet indicator light or switch does not respond
  • Warning message about the power outlet or external power supply
  • Plugged-in equipment will not run or cuts out
  • Other high-voltage system or hybrid warnings may appear alongside, depending on the model

Possible causes

  • Damaged, corroded or water-affected outlet socket or its internal contactslikely
  • Open circuit, chafed wiring or poor connection between the converter and outlet Blikely
  • Loose, corroded or pushed-out pins at the converter or outlet connectorlikely
  • Blown fuse or tripped protection device in the outlet circuit, usually caused by an overload or shortpossible
  • Fault inside DC/AC converter A, such as a failed output stagepossible
  • Faulty outlet switch or enable signal, or a control module faultrare
  • Outdated control unit software where the manufacturer has documented a fix for this faultrare

How to diagnose

  1. Read all stored codes and freeze frame data, noting whether any other high-voltage, converter or battery codes are present, and check whether the code is current or historic.
  2. Ask what was plugged into the outlet and whether it was overloaded or damaged, and check whether the outlet works with a known good low-power load.
  3. Visually inspect outlet B for water, debris, burn marks, bent contacts or heat damage.
  4. Check the fuse and any protection device for the outlet circuit against the vehicle's wiring information.
  5. Inspect the wiring and connectors between the outlet and converter for chafing, pin damage, corrosion or moisture, without touching any orange high-voltage cabling.
  6. Check that the outlet enable conditions are met, such as switch position and vehicle ready state, using the manufacturer's procedure.
  7. Test circuit continuity and resistance at the low-voltage control side as specified by the manufacturer; leave high-voltage testing to technicians trained and equipped for it, following the shutdown and isolation procedure.
  8. Look for manufacturer service bulletins or software updates relating to the converter or outlet for this model.

How to fix

  • Repair or replace damaged wiring and clean or replace corroded or loose connectors.
  • Replace the faulty outlet socket assembly if contacts are damaged or water-affected.
  • Replace a blown fuse only after finding and fixing the cause of the overload or short.
  • Replace or repair DC/AC converter A if testing shows an internal fault, using the manufacturer's high-voltage procedures.
  • Replace a faulty outlet switch or control module if diagnosis confirms it.
  • Update the control unit software only if the manufacturer lists an outdated calibration as a known cause for this code.

Can I keep driving?

Low severity

The fault normally affects only the power outlet, so the car can usually be driven while you book it in. Do not use the outlet, and stop and seek help if hybrid or high-voltage warning lights come on, or if you notice a burning smell or heat from the socket.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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