"Check Hybrid System" on your Lexus or Prius: the inverter overheated
A dealer quotes $4,500 to $6,500 to replace the complete inverter-converter assembly on a Lexus RX450h or a Toyota Prius, with weeks of backorder and mandatory towing. The dealership doesn't repair this module: it replaces the whole thing. But what collapses inside is almost always a power subboard, and the cause isn't mileage — it's cooling.
Loss of traction and a No-READY state
Pick the symptom to see the likely cause
A dull thud in the engine bay and the throttle stops responding
The traction stage transistors were perforated and the system cuts power immediately.
What the inverter does and why heat kills it
The assembly Denso builds is the switching brain of the hybrid powertrain: it steps the 288V DC coming from the rear battery up to 650V three-phase AC to feed the motor generators. The IGBT transistors in the power module switch currents above 150 amps, thousands of times per second.
Air can't carry that heat away: the inverter has its own liquid cooling circuit, with its own electric water pump, independent of the engine. When that pump loses flow through wear, or the radiator packs with debris, the temperature at the transistor's silicon junction passes 300 °F and the dielectric barrier is perforated. In Miami's climate that margin runs out far sooner than in other markets.
What the HV ECU logs
P0A94 — DC/DC Converter Performance: collapse of the conversion to 12VP0A7A — Generator Inverter Performance: transistor failure in the MG1 generatorP0A78 — Drive Motor Inverter Performance: destruction in the MG2 traction stageP3004 — High Voltage Power Cable Malfunction: secondary electrical arcing⚠ burned component: intelligent power module (IPM) with IGBT transistorsThis is high voltage: 288V DC at rest and 650V AC in operation. The work is done with the high-voltage capacitors discharged on a safe bench and under an isolation protocol. This is not a module to open at a general shop or in a home garage.
Message us on WhatsAppThe platforms we service
Lexus RX400h and RX450h
Heavy vehicles whose transistors work under extreme load moving the SUV's mass. Highly susceptible if the front radiator packs with debris or the pump loses efficiency.
Toyota Prius (Gen 3) and Camry Hybrid
We diagnose P0A94 and P0A78 routinely on rideshare units, subjected to continuous stop-and-go traffic over hot asphalt.
Toyota Highlander Hybrid
Shares the heavy electronic architecture of the RX series and shows the same boost converter collapses.
Lexus CT200h and ES300h
They degrade in the DC-DC conversion circuit that charges the 12V auxiliary battery, and the vehicle is immobilized for lack of low voltage to the onboard computers.
How we repair it
- Step 01
Safe-bench triage
We discharge the high-voltage capacitors and analyze the logic control stage and the power board on a scope, to confirm the IGBTs are perforated.
- Step 02
Power-stage micro-surgery
We remove the burned transistor module without damaging the expensive control board or the current sensors.
- Step 03
Reinforced silicon
We solder in industrial-grade power components with higher operating temperature thresholds than the factory parts.
- Step 04
Renewed heat transfer
We clean the aluminum heat sink base and apply aerospace-grade 8.5 W/mK thermal elastomers, which is what removes the hot spots and keeps the defect from repeating.
- Step 05
Immobilizer preserved
Keeping the original inverter control ECU means the Smart Key algorithm is untouched and the car never learns the module came out.
The inverter comes back ready to install. Your mechanic refits the aluminum block, connects the high-voltage harness and properly bleeds the air from the inverter coolant — that step isn't optional — and the vehicle enters READY immediately.
Hybrid lost traction and won't go back into READY? Let's evaluate the inverter before replacing the whole thing.
Is your car showing any of these problems? Message us now.