P0C78
Hybrid/EV Battery System Precharge Time Too Long
The HV battery system precharge time is longer than the calibrated window. Indicates high resistance, weak contactor, or aged components.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: hard
Symptoms
- EV/hybrid system warning light on
- Reduced power output or limp mode
- Charging may fail or be slowed
- Reduced electric range
Common causes
Ordered by how often each turns out to be the cause.
- Increased resistance in pathCommon
- Contactor coil weakeningPossible
- Pack cell imbalance approaching service thresholdLess likely
Parts involved
- Hv Battery System
- Precharge Resistor
- Main Contactors
P0C78 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.