Powertrain, generic (extended)

P2C87 Hybrid/EV Battery Voltage External Isolation Warning

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

P2C87 is the warning stage for weakening insulation outside the battery, on the vehicle-side high-voltage network. Many systems use two limits; Volkswagen's ID.4, for example, shows a yellow lamp below 510 kOhm and a red one below 90 kOhm. Mercedes-Benz stores P2C8700 for an insulation warning on the vehicle side, listed in its 2024 extended warranty for plug-in hybrids with a corroding high-voltage A/C compressor and in a 2025 bulletin on a moist PTC heater. Volvo logs P2C871A in the BECM of the EX30: if it appears together with P128300 in VCU1 and the car will not engage a gear or reports reduced power, Technical Journal 37771 has the combined charger and DC/DC module replaced. If the fault grows, P2C85 follows.

Likely causes

Moisture or corrosion in an external HV component (compressor, heater, charger)
Insulation fault inside the on-board charger or DC/DC converter
Dirty or wet high-voltage connector

Symptoms

  • Yellow high-voltage or battery warning
  • Reduced power or no gear engagement on some models
  • Intermittent, often after rain or washing

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€200–4,000
Time1–8 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

hv batteryhv wiringisolation monitor

Related codes

P2C85P2C88P2C86P0AA6P0DAA

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov, batterydesign.net.