P2C85Hybrid/EV Battery Voltage External Isolation Fault
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- P2C85 means the isolation monitor has found a fault-level loss of insulation on the vehicle side of the battery, in cables or components connected through the contactors. Mercedes-Benz uses the code in the battery management system with the text vehicle-side insulation fault. A 2024 warranty notice for C 350e, GLC 350e, GLE 550e and S 550e/560e plug-in hybrids lists it for a corroding high-voltage A/C compressor winding; the car could not be restarted once switched off. A 2025 bulletin for the 295, 296 and 297 model series traces it to moisture in a high-voltage PTC heater without a diaphragm. External versus internal follows from where the resistance is measured, as a Magna patent separates battery and component insulation. P2C87 is the earlier warning stage, P0AA6 the system fault.
- What you may notice
- Red high-voltage or battery warning, do not restart message
- Vehicle cannot be restarted after switching off
- Electric heater or A/C not working
- Likely causes
- LikelyInsulation breakdown in the high-voltage A/C compressor
- PossibleMoisture in the high-voltage PTC heater or its connector
- PossibleChafed or crushed high-voltage cable touching the body
- RareCoolant or water inside inverter, motor or charger
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €300 – €4,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.