OBD-II trouble code
P0A78: Drive Motor A Inverter Performance
Application matters: Toyota T-SB-0386-08 describes certain 2006–2008 Highlander HV applications with information code 286 and/or 287 and a production-change restriction. Match the complete code and actual vehicle before applying that repair.
Preserve the complete drive-motor A inverter fault report, including any information code. Toyota’s cited Highlander repair applies to specific 286/287 cases.
Quick facts
- System
- Powertrain
- Category
- Hybrid Propulsion
- Severity
- High severity
- Driving guidance
- Stop safely and arrange diagnosis
- Repair cost range
- Get a vehicle-specific estimate after diagnosis.
- DIY difficulty
- Shop recommended
A code alone cannot establish whether driving is safe. Stop safely for a red brake or oil-pressure warning, overheating, severe misfire, stalling, or impaired braking or steering, and follow the owner's manual. Restraints faults can reduce crash protection even when the vehicle runs normally.
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What does P0A78 mean?
P0A78 identifies a drive-motor A inverter performance condition. Preserve the complete manufacturer report, including any information code, because the five-character label does not select one failed component or repair. It does not establish the condition of the hybrid battery, motor windings or associated wiring.
Toyota’s December 16, 2008 bulletin T-SB-0386-08 provides a concrete example for listed 2006–2008 Highlander HV vehicles with the 3MZ engine. Its entry conditions specifically require information code 286 and/or 287, and the vehicle must meet the bulletin’s production-change criteria. A different information code is not permission to apply this repair.
For that matching condition, Toyota specifies replacing the inverter with converter assembly using the applicable vehicle repair procedure. That is an application-specific assembly repair, not proof that every inverter performance report has the same internal cause. A technician must check the complete fault record and the current service information for the particular vehicle.
Record the warning messages, whether the vehicle entered READY, any loss of propulsion and recent hybrid-system work. Do not repeatedly restart, clear codes or accelerate to see whether the fault returns. Those actions can remove useful evidence or place the vehicle in an unsafe situation without establishing a diagnosis.
Inverter diagnosis and replacement involve protected high-voltage work. Leave cover removal, service plugs, electrical testing, coolant access and component handling to qualified hybrid service personnel. Follow the vehicle’s warnings and recovery instructions; obtain assistance if it cannot operate normally. The code does not establish a safe driving distance or guarantee engine-only operation.
Possible causes
- An inverter/converter assembly condition in the matching Highlander bulletin case
- Another drive-motor inverter or associated system fault established through the actual vehicle’s diagnosis
Symptoms
- A check-engine or hybrid warning with the full P0A78 report
- Reduced or unavailable propulsion if the actual fault affects operation
- A warning recorded without enough information on a basic reader to select the applicable repair
Diagnostic steps
Save the full scan report, code status, and available freeze-frame data before clearing anything. Confirm the reporting module, any failure-type suffix, and the procedure for the exact vehicle. The steps below are an overview; use manufacturer specifications and safety procedures for testing.
- 1.Record the full DTC, information code, companion faults and available event data before anything is cleared. Note warnings and symptoms already observed.
- 2.Arrange qualified hybrid diagnosis and have the technician identify the drive-motor inverter referenced by the actual vehicle’s information.
- 3.For the cited Highlander example, verify the model, production criteria and information code 286 and/or 287. Do not transfer that bulletin to another information code or vehicle.
- 4.Ask which diagnostic findings or applicable service instructions support the proposed assembly work. A battery, motor or inverter purchase should not be based only on the title.
- 5.Have the confirmed repair, required setup and verification completed professionally. Do not open high-voltage equipment or reproduce the fault on the road.
Repair cost
Get a vehicle-specific estimate after diagnosis.
A trouble code alone does not price the repair. Ask the shop to identify the confirmed fault and itemize diagnosis, parts, labor, programming or calibration, and taxes.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with qualified hybrid-system diagnosis preselected. Adjust labor rate and vehicle category to fit your situation.
Related repairs
These links are planning examples; the code does not confirm that any listed part has failed.
DIY vs shop
A qualified shop is recommended because this can involve a high-voltage traction system that stays live with the car switched off and requires documented shutdown procedures, in-date insulating gloves, and specific training. Ask the technician what testing confirmed the repair.