P0C78 means precharge took too long: the inverter side did not come up to battery voltage within the allowed time. GM's 2011 Volt allows 700 ms to reach 95 % (Type A), the 2013 eAssist 1,000 ms or more than 5 A for over 100 ms (Type B), and the 2019 tables demand 95-105 % at 0.700 s, Type A. The 2018 Outlander PHEV flags a gap of 12 V or more between battery and inverter after 1 s. Typical causes are an open precharge resistor or fuse, a high-voltage load pulling the bus down, and software. Bulletins cover a blown fuse in the service disconnect (Bolt EV, 18-NA-225), a failed coolant heater (Spark EV, 16-NA-072) and battery-module software at Chrysler and Volvo. The vehicle then normally will not become ready.
High severity. Can I keep driving?If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.
Symptoms
- Vehicle does not become ready to drive
- Malfunction indicator lamp and drive system message
- Loss of propulsion
Most likely causes
- Precharge resistor, precharge contactor or high-voltage fuse open
- Faulty high-voltage consumer such as a coolant heater loading the bus
- Battery module software, fixed by an update
- Loose high-voltage cable or bus bar
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- It can trigger limp mode.
- It affects emissions.
What each character of P0C78 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- C: Subsystem depends on the code range
- 78: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0C78?
If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.
What causes code P0C78?
The most common causes are: precharge resistor, precharge contactor or high-voltage fuse open; faulty high-voltage consumer such as a coolant heater loading the bus; battery module software, fixed by an update.
Related codes
- P0C77Hybrid/EV Battery System Precharge Time Too Short
- P0C76Hybrid/EV Battery System Discharge Time Too Long
- P0C75Hybrid/EV Battery System Discharge Time Too Short
- P0AE3Hybrid/EV Battery Precharge Contactor Circuit Stuck Open
- P0D26Battery Charger System Precharge Time Too Long
Sources
- gsi.ext.gm.com: 19OBDG01 Hybrid Diagnostics
- gsi.ext.gm.com: 11OBDG01 HYBRID Diagnostics
- mitsubishitechinfo.com: M154923210015000USA
- static.nhtsa.gov: MC 10165091 9999
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.