P0A78 on Chevrolet: How to Diagnose & Fix
Drive Motor A Inverter Over-Temperature
1 Chevrolet model · 1 documented issue · 1 critical · $600-$1,800 repair
P0A78 on Chevrolet by model: symptoms, diagnosis and fix
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)
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 on a Chevrolet?
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. On Chevrolet it is documented across 1 model: Bolt EUV.
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 on a Chevrolet?
Published repair estimates on Chevrolet range from $600 to $1,800 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0A78 on a different make?
View P0A78 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.