P0A05 on Toyota: How to Diagnose & Fix
Motor Electronics Coolant Pump "A" Control Circuit/Open
1 Toyota model · 1 documented issue · 1 critical · $700-$1,100 repair
P0A05 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)
P0A05 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 P0A05 mean on a Toyota?
P0A05 stands for "Motor Electronics Coolant Pump "A" Control Circuit/Open." The control circuit for the motor electronics (inverter) coolant pump 'A' is open or not responding as commanded. This electric pump circulates coolant through the inverter/power-electronics loop. On Toyota it is documented across 1 model: Highlander.
What are the most common causes of P0A05?
The most common causes of P0A05 are: Failed electric coolant pump, Open in pump control wiring/connector, Blown fuse or relay, Control module driver fault. The specific cause varies by vehicle.
How much does it cost to fix P0A05 on a Toyota?
Published repair estimates on Toyota range from $700 to $1,100 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 P0A05 on a different make?
View P0A05 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.