EV and hybrid code
P0A78: Drive motor inverter performance problem
How this range is built
| Part of the job | Low | High |
|---|---|---|
| Parts | $800 | $3,500 |
| Labor: 2 to 5 hours × $125 to $175 an hour | $250 | $875 |
| Fees: shop supplies, disposal, diagnostics | $0 | $100 |
| Total, rounded | $1,050 | $4,475 |
The hourly rate is the BLS Occupational Employment and Wage Statistics, May 2025 average pay for this trade in Boston, $31.54 an hour, times 4 to 5.5 to cover what a shop bills (overhead, tools, insurance, profit). Parts are a band from budget aftermarket to the manufacturer part. Full method.
Not a repair shop, estimates only. Typical range, estimate. Not a quote. Your car, parts and shop change the number.
This is the range for the most common fix, hybrid inverter / converter repair. Which repair your car needs depends on a proper diagnosis.
The inverter that runs the electric drive motor is not working as expected. This is the usual meaning, but it varies by make, so check the scan tool or manual. Heat and cooling problems are frequent causes, and low coolant or a weak pump can make the inverter limit power or stop.
- Safe to drive?
- No, get it looked at first
- Most common cause
- Inverter cooling problem
Stop driving if power drops, the car shakes, or a red warning shows. Stop driving if the car goes into limp mode, shows a red warning, loses power, or you smell something burning. Call a tow rather than keep driving.
What you may notice
- Hybrid warning light on
- Reduced power
- Car won't go in ready
- Warm or hot smell
Common causes, most likely first
- Inverter cooling problem
- Failing inverter
- Bad connection
- Low coolant
- Motor fault
Check this first
Check the inverter coolant level and that the cooling pump runs. Do not open high voltage covers.
Other repairs that sometimes fix P0A78
| Repair | Typical range, Boston |
|---|---|
| EV battery coolant service / pump | $190 to $1,300 |
| High-voltage battery inspection and service | $120 to $880 |
| Diagnostic scan (check engine light) | $60 to $290 |
Before you pay
- Ask the shop what test showed this part is the cause, not just that the code appeared.
- Ask for parts and labor listed separately, and for the hours.
- Ask for a written OK before any extra work. Massachusetts rules require written authorization before repairs.
Got a quote already? Check it against the range. Want to see if your car has a recall tied to this problem? Check recalls by VIN.
Need to read a code yourself? OBD-II scanners on eBay (affiliate link, disclosure).
P0A78 questions
Is the inverter expensive?
It is usually one of the pricier hybrid parts, so confirm the cause first. A shop should test the cooling system and wiring before suggesting an inverter replacement.
Can cooling cause it?
Yes. Weak cooling often limits the inverter or damages it over time. Checking the coolant level and the pump costs little and can prevent a much larger repair.
Is it covered by warranty?
Many makes cover hybrid parts for a long period, and some inverters are covered as part of the hybrid system. Check your paperwork or ask a dealer before paying out of pocket.
How much does it cost to fix P0A78?
The most common fix, hybrid inverter / converter repair, has a typical range of $1,050 to $4,475 in Boston. It is an estimate built from parts prices and local labor wages, not a quote. Your car and shop change it.
Related codes
- P0A93: Inverter cooling system problem
- P0A94: DC/DC converter performance problem
- P0AA6: High voltage isolation fault
More ev and hybrid codes
Code meaning written in our own words. Some codes mean different things on different makes, so check your scan tool or manual. Not a repair shop, estimates only.