Powertrain, generic · Hybrid propulsion

P0C85 Hybrid/EV Battery Temperature Sensor H Circuit Intermittent/Erratic

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P0C85 points to a sensor H reading that flickers. A battery pack warms and cools slowly, so fast swings in one channel suggest an electrical contact problem rather than real heat. GM's 2018 hybrid table 18OBDG02 adds up how much the value moves within a 10-sample window at 100 ms per sample; once that sum passes 10 in 4 of 5 evaluations, the module logs P0C85, Type B over two trips, as long as the supply exceeds 10.2 V and the battery interface module is talking. The 2019 table 19OBDG02 keeps the same rule. GM's OBDG01 tables of 2011 to 2016 (first-generation Volt, ELR) and Mitsubishi list no such code for sensor H. A wiggle test on the harness while watching live data usually finds the fault; low or high voltage faults are P0C83 and P0C84 instead.

Likely causes

Intermittent contact at the sensor H terminal
Partly broken sensor H wire inside the pack harness
Noisy measuring channel on the sensing board

Symptoms

  • Intermittent warning lamp
  • Sensor H value jumping in live data

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–2,500
Time1–5 h

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

Parts involved

hv battery temp sensor hwiring harnessbms

Related codes

P0C81P0C82P0C83P0C84P0C80P0C8C

References: gsi.ext.gm.com, gsi.ext.gm.com, law.cornell.edu.