P0A78: How to Diagnose & Fix — Drive Motor A Inverter Over-Temperature
4 vehicles · 3 makes · $200-$6,000 repair
How to diagnose and fix P0A78: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Nissan Leaf · 2011–2017
The 2011-2017 Leaf traction motor inverter can fail, resulting in complete loss of propulsion. The inverter converts DC battery power to AC for the motor. Symptoms include sudden power loss, error messages, and the vehicle going into turtle mode. This is a costly repair outside warranty.
Common Symptoms
- Sudden loss of power
- Turtle mode indicator
- Multiple warning lights on dash
- Vehicle won't accelerate
- EV system warning message
How to Fix
Diagnose with Nissan CONSULT to confirm inverter failure. Replace traction motor/inverter assembly. Cost: $3,000-6,000 at dealer. Used/refurbished inverters from salvage Leafs available for $1,500-2,500. Check if covered under EV powertrain warranty (8yr/100k miles).
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Nissan 2013-2017 LEAF power inverter 291A0-3NF0B
Confirm VIN, build and installed assembly.
- Genuine Nissan 2011-2012 LEAF traction motor and inverter drive unit 290J0-3NA1A
Confirm VIN, installed assembly, warranty, freight/core terms and non-returnability before purchase.
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Sources for this issue (1)
Toyota Prius C · 2012–2019
The Prius C has a separate cooling circuit for the power electronics (inverter/converter). The electric pump that circulates coolant through this circuit can fail, causing the inverter to overheat. When the inverter overheats, the hybrid system enters a protective shutdown mode, displaying "Hybrid System Malfunction" and severely limiting power output. The pump failure is often caused by coolant contamination or bearing wear.
Common Symptoms
- Hybrid System Malfunction warning message
- Triangle warning indicator (master caution) illuminated
- Reduced power output / vehicle feels sluggish
- No EV-only mode available
- Inverter cooling fan running at high speed constantly
How to Fix
Replace the inverter coolant pump (Toyota G9040-52010). Flush the inverter cooling circuit with distilled water then refill with Toyota Super Long Life Coolant (SLLC). Check the inverter coolant reservoir for contamination — brown or rusty fluid indicates the pump has been shedding bearing material. The pump is accessible from the engine bay and is a 1-hour repair.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Toyota G9040-52010 inverter water pump assembly with motor
replace a confirmed failed inverter coolant pump and restore/bleed the inverter cooling loop Fitment/availability: 2012-2018 Prius C 1.5L 1NZ-FXE inverter cooling circuit; source year 2019 requires VIN confirmation because the live catal…
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Owner tips & cautions
- TipChange the inverter coolant every 100,000 miles with Toyota SLLC — most owners forget this separate cooling circuit exists
- WarningDo not ignore the Hybrid System Malfunction warning — continued driving with an overheated inverter can destroy the power electronics ($3,000+ replacement)
Sources for this issue (3)
Chevrolet Bolt EUV · 2022–2023
GM TSB 19-NA-220, revised February 2023, explicitly covers 2022-2023 Chevrolet Bolt EUV. Customers experience an outright loss of propulsion - the car stops driving - and history codes P0A3F and sometimes P1B03 are stored in the Hybrid/EV Powertrain Control Module. The vehicle often operates normally again after a restart, which makes it dangerous and hard to catch. The cause is a spread (splayed) terminal at harness connection X2 on the T12 transmission/drive unit assembly, where terminals were not perfectly aligned during installation at the assembly plant. GM warns that terminals need not show visible damage to set the codes. Because these are resolver (motor position sensor) circuits, this is a genuine drive-unit interface failure, not a software trip, and it can drop propulsion at speed.
Common Symptoms
- Sudden complete loss of propulsion while driving
- Vehicle drives normally again after a restart
- Malfunction indicator lamp illuminated
- Intermittent, hard to reproduce at the dealer
How to Fix
Replace the engine wiring harness. GM explicitly prohibits splicing in a terminated lead at this connector because of the sensitivity of the resolver circuits (SI document ID 4583435). On reassembly the connector bodies must be aligned squarely and not entered at an angle, or the failure repeats. Important diagnostic caveat: if P0A78, P0C01 or P0C0B are also present alongside P0A3F/P1B03, the harness is likely NOT the cause and GM Technical Assistance must be contacted - do not let a shop replace the harness on those codes. Covered under the EV powertrain warranty on most surviving EUVs.
Sources for this issue (1)
Toyota Highlander · 2006–2010
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P0A78 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 P0A78 mean?
P0A78 stands for "Drive Motor A Inverter Over-Temperature." P0A78 is a hybrid/electric-vehicle code indicating that drive motor 'A' inverter has overheated. The inverter converts the high-voltage battery's DC power into AC to drive the electric traction motor, and it has temperature sensors; when the inverter temperature exceeds safe limits, the control module sets this code and usually reduces power to protect the components. Symptoms include reduced power (limp mode), warning lights, or in severe cases the vehicle refusing to drive. It points to an inverter cooling or electronics problem in the high-voltage drive system rather than the gasoline engine.
What are the most common causes of P0A78?
The most common causes of P0A78 are: Low coolant or air in the inverter cooling loop, Failed inverter/electronics coolant pump, Clogged or restricted inverter cooling passages/radiator, Faulty inverter temperature sensor, Failed or degrading inverter/power module, Cooling fan or thermostat fault in the inverter loop, Excessive load or related high-voltage system fault. The specific cause varies by vehicle.
How much does it cost to fix P0A78?
Repair costs for P0A78 range from $200 to $6,000, depending on the vehicle and root cause.
Which vehicles are affected by P0A78?
Au7o has documented P0A78 across 4 vehicle models from 3 manufacturers: Chevrolet, Nissan, Toyota.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.