Powertrain, generic (extended)

P2C88 Hybrid/EV Battery Voltage System Isolation Warning

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

P2C88 is the warning counterpart to P0AA6: the isolation resistance of the high-voltage system as a whole has fallen below a first limit without the monitor yet being able to say whether the battery or the vehicle side is to blame. Mercedes-Benz uses P2C8800 in the battery management system of the 295, 296 and 297 model series; its 2025 bulletin lists it with P2C8500 and P2C8700 when moisture builds up in a high-voltage PTC heater lacking a diaphragm, a fault that starts sporadically and worsens. Legally the complete system must stay above 500 ohms per volt, so the warning leaves time to find the leak before a lockout. Measure each branch separately, starting with components that are switched in only at times.

Likely causes

Moisture in a high-voltage component that is only switched in at times (heater, compressor)
Gradual insulation aging in cables or connectors
Beginning insulation loss inside the battery pack

Symptoms

  • High-voltage warning message, sometimes towing not allowed notice
  • Electric heater stays cold if it is the leaking part

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

P0AA6P2C85P2C86P2C87P0E74

References: static.nhtsa.gov, batterydesign.net, law.cornell.edu.