P0A78: How to Diagnose & Fix — Drive Motor 'A' Inverter Performance
3 vehicles · 2 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 the EV system warranty (5yr/60k miles); the 8yr/100k coverage applies to the lithium-ion battery only. 2014 Leafs built April 15-24, 2014 are covered by recall 14V263 (free inverter replacement).
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 (3)
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)
Toyota Highlander · 2006–2010
On the first- and second-generation Highlander Hybrid (2GR-FXE / 3MZ-FE hybrid), the Intelligent Power Module inside the hybrid inverter assembly carries control-board transistors whose operating temperature can exceed what the solder beneath them tolerates. The solder degrades, the transistor is heat-damaged, and the hybrid system throws multiple warning lamps. In most cases the vehicle drops into fail-safe/limp-home mode with sharply reduced power; in worse cases the power-supply-circuit fuse blows and the entire hybrid system shuts down while driving, stalling the vehicle. This is distinct from the inverter coolant pump failure and from HV traction-battery degradation — here it is the power electronics themselves, not the cooling loop or the pack. Toyota first recalled 2006-2007 cars (11V342000) and then broadened it to all 2006-2010 Highlander Hybrids built Feb 2005 through Jul 2010 under 13V396000 / Toyota campaign D0M.
Common Symptoms
- Multiple warning lights on at once — check engine, slip indicator, brake system, master warning
- Sudden loss of power / limp-home mode
- Hybrid system shuts down and vehicle stalls while driving
- Vehicle will not restart after shutdown
- Reduced acceleration, dashboard warning chime
How to Fix
Free recall remedy: dealers replace the Intelligent Power Module inside the inverter assembly at no cost under NHTSA 13V396000 (Toyota D0M) — check the VIN at nhtsa.gov/recalls, because many of these cars have changed hands several times and never had it done. If the VIN is not covered or the campaign has been performed and the fault returns, the repair is inverter assembly replacement (or specialist IPM board rework), which is the expensive path.
Sources for this issue (4)
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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 Performance." P0A78 is a hybrid/electric-vehicle code indicating that the drive motor 'A' inverter is not performing as expected. The inverter converts the high-voltage battery's DC power into AC to drive the electric traction motor; when the control module sees abnormal inverter behaviour, such as phase current that does not follow the command, an internal switching or protection fault, or an inverter temperature problem, it sets this code and usually reduces or cuts power to protect the components. Symptoms include reduced power (limp mode), warning lights, or the vehicle refusing to drive. It points to the high-voltage drive inverter or its cooling rather than the gasoline engine.
What are the most common causes of P0A78?
The most common causes of P0A78 are: Internal inverter/power module fault (switching device or gate driver), 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, Inverter software/calibration fault, Related high-voltage system or motor 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 3 vehicle models from 2 manufacturers: Nissan, Toyota.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.