P0A94: How to Diagnose & Fix — DC/DC Converter Performance

Condensation can form inside the Onboard Charger with integrated DC/DC converter (OCDC, a Bosch-supplied unit) because the printed circuit board lacks sufficient protective conformal coating. Moisture causes electromigration on the PCB and the OCDC fails, so it can no longer charge the 12-volt battery from the high-voltage pack. The result is non-start conditions, and if driven until the 12V battery depletes, a loss of motive power and electronically assisted functions. This is a hardware charger failure, separate from ordinary 12V auxiliary battery drain. NHTSA recall 25V125 covers MY2024 ID.4 (and related Audi Q4 e-tron).

Toyota/NHTSA Safety Recall 23V-478 (Toyota 23TA07) covers certain 2021-2022 RAV4 Prime vehicles. A current-rectifying module inside some DC-DC converters may have been damaged during supplier production. If the module fails, it can short rather than open, allowing current from the 12V battery to continue through the module and generate heat. Excessive heat can damage components inside and outside the converter and increase fire risk. Toyota reports the actual damaged-module percentage as unknown; model year alone does not establish VIN eligibility.

NHTSA campaign 25V125 / Audi 93FR covers certain 2024-2025 Q4 e-tron and Q4 e-tron Sportback vehicles. The on-board charger can fail and stop charging the 12-volt battery, which can lead to loss of drive power and increase crash risk. Eligibility is VIN-specific; this does not support the former universal sensor, relay, battery or software-glitch diagnosis.

NHTSA campaign 23V449000 recalls BMW iX, i4 and i7 vehicles whose Combined Charging Unit was not manufactured correctly, leaving internal components improperly connected or assembled. The important distinction for iX owners is the failure mode: this campaign is not about AC charging refusing to work, it is about the CCU interrupting electrical power while the vehicle is in motion. NHTSA records the consequence as an improperly assembled CCU that 'can interrupt power and cause engine stall, increasing the risk of a crash.' On the iX the CCU is the combined on-board charger and DC/DC converter, so a fault there simultaneously threatens both traction power and the 12V supply that runs steering assist, brake assist and lighting. This is consistent with the 2023 iX complaint file, which contains multiple reports of losing propulsion and, in the worst cases, of losing power-assisted steering and braking together at speed - one complainant describing that they 'lost power assisted steering AND power assisted braking. I had to decelerate with no power brakes.' The remedy is replacement of the CCU, not a software update.

Transistors inside the Intelligent Power Module of the inverter/converter assembly can overheat and fail under sustained high load (long grades, hard acceleration, hot weather). When the module faults, the hybrid system shuts down and the car can stall at speed, sometimes without warning. Toyota first issued a software recall to reduce IPM thermal stress (NHTSA 14V-053, ~701,000 US Gen 3 cars), later expanded remedies (18V-684), and created Customer Support Program ZE3 extending inverter coverage on 2010-2014 Prius to 15 years/unlimited miles. Owners report stalls persisting after the software remedy, which drove follow-on litigation. This is failure of the inverter itself - distinct from the inverter coolant pump.