P0A94 on Toyota: How to Diagnose & Fix
DC/DC Converter Performance
3 Toyota models · 3 documented issues · 3 critical · $700-$5,000 repair
P0A94 on Toyota by model: symptoms, diagnosis and fix
The Highlander Hybrid uses a dedicated electric water pump to circulate coolant through the power inverter/converter, which runs separately from the engine cooling system. The electric pump wears out and stops circulating coolant, allowing the inverter and hybrid electronics to overheat. Failures often present with little warning beyond a check engine light and hybrid warning lights; if ignored, the inverter itself (a far more expensive component) can be damaged. Owners report this most on the 2006-2010 generation but it recurs across later hybrids.
Common Symptoms
- Check engine and hybrid system warning lights
- Inverter coolant leak / low inverter reservoir
- Reduced hybrid power or limp mode
- Overheating of the hybrid/inverter system
How to Fix
Replace the inverter cooling electric water pump and refill/bleed the inverter coolant loop (air-bleed procedure is required). For the 2006-2010 Highlander Hybrid the drive-motor inverter cooler water pump is Toyota PN G9040-48080 (non-tow); tow-package and later years use a different pump (e.g., G9020-48xxx family) so verify by VIN/configuration. Expect roughly $700-$1,100 done by a competent shop (pump ~$220-$290 plus diagnosis/labor and coolant). Catch it early — replacing the pump is far cheaper than an overheated inverter.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Toyota G9040-48080 genuine drive-motor inverter cooler water pump
early-generation inverter-loop pump after flow and electrical diagnosis proves failure Fitment/availability: VIN-confirmed 2006-2010 Highlander Hybrid MHU23/MHU28 and applicable early MHU48 branch; verify production date and tow/cooling …
- Toyota G9040-47090 genuine inverter water pump assembly
middle production branch pump after inverter-loop diagnosis Fitment/availability: VIN- and production-date-confirmed 2010-2013 Highlander Hybrid branch; replaces G9040-48020 on applicable vehicles Fitment/availability: Live direct produc…
- Toyota G9040-52010 genuine inverter water pump assembly
later second-/early third-generation inverter-loop pump Fitment/availability: Production-date-confirmed 2012-2016/early-2017 Highlander Hybrid branch; reviewed catalog shows 10/2012-02/2014 and 01/2014-11/2016 applications Fitment/availa…
- Toyota G9040-52020 genuine inverter water pump assembly
late third-generation inverter-loop pump after flow and electrical testing Fitment/availability: VIN-confirmed late-2016 through 2019 Highlander Hybrid 3.5L branch; catalog production change begins 11/2016 Fitment/availability: Live dire…
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Sources for this issue (3)
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.
Common Symptoms
How to Fix
Check the complete VIN through Toyota's recall lookup or an authorized Toyota dealer. The current 23TA07 remedy replaces the DC-DC converter with an improved part free of charge. The earlier cold-temperature charging restriction was interim guidance and should not replace completion of the available remedy. If heat, smoke or a burning odor is detected, stop safely, switch the vehicle off, move occupants away and contact emergency services as conditions require. Do not diagnose an open recall from generic warning lights, a no-start or a discharged 12V battery alone.
Owner tips & cautions
- TipUse the complete VIN to check 23TA07 eligibility; 43,442 is the total RAV4 Prime/Lexus recall population, while Toyota lists approximately 41,500 covered RAV4 Prime vehicles.
- WarningThe improved-converter remedy is available; do not rely on the old temporary cold-weather charging restriction instead of completing the recall.
Sources for this issue (3)
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.
Common Symptoms
- Vehicle stalls or loses power at highway speed
- Red triangle hybrid warning and check engine light
- Limp-home / reduced power mode
- Car will not restart until cooled or after a reset
- Burning smell from under the hood in severe cases
How to Fix
Verify the recall/CSP status by VIN at the NHTSA or Toyota owners site and have the software remedy applied if outstanding. If the IPM has actually failed, the fix is replacement of the inverter/converter assembly (Toyota does not sell the IPM separately), followed by a full inverter coolant fill and air bleed - and the inverter coolant pump should be checked at the same time, because a weak pump is a common contributor to IPM overheating. Push for ZE3 coverage on 2010-2014 cars before paying out of pocket.
Sources for this issue (3)
P0A94 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0A94 mean on a Toyota?
P0A94 stands for "DC/DC Converter Performance." This hybrid/electric vehicle code sets when the hybrid control system detects that the DC/DC converter is not performing within expected parameters. The DC/DC converter steps the high-voltage battery power down to the 12-volt level that runs the car's lights, accessories, and control modules, so a performance fault can affect the whole low-voltage system. Symptoms may include warning lights, reduced power, the hybrid system not starting, or a discharged 12-volt battery. Because high-voltage components are involved, diagnosis and repair should be done by a qualified hybrid technician. On Toyota it is documented across 3 models: Highlander, RAV4, Prius.
What are the most common causes of P0A94?
The most common causes of P0A94 are: Faulty inverter/converter assembly (DC/DC converter), Open or shorted wiring in the converter circuit, Poor electrical connection at the converter, Weak or failing 12-volt battery, High-voltage system or cooling fault affecting the converter, Software/control module calibration issue, Faulty hybrid control module (less common). The specific cause varies by vehicle.
How much does it cost to fix P0A94 on a Toyota?
Published repair estimates on Toyota range from $700 to $5,000 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0A94 on a different make?
View P0A94 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.