Powertrain, generic · Hybrid propulsion

P0C91 Hybrid/EV Battery Temperature Sensor J Circuit Intermittent/Erratic

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P0C91 watches for a sensor J reading that changes too fast and too often for a heavy battery. GM's tables 16OBDG02 and 19OBDG02 add up how far the value moves between samples over a 10-sample window taken every 100 ms; a sum above 10 fails the window, and 4 failing windows out of 5, about half a second, store the code, Type B over two trips. The check needs more than 10.2 V and working communication. The reading may stay within its valid range, which distinguishes P0C91 from P0C8F and P0C90. Mitsubishi's PHEV has nothing comparable for this channel. Likely culprits are a worn contact or a conductor broken under its insulation; if neighbouring sensors jump at the same moment, suspect the monitoring board.

Likely causes

Fretting or loose terminal in the sensor J plug
Conductor broken inside the insulation, opening under vibration
Unstable reference or ground on the monitoring board

Symptoms

  • Warning lamp that comes and goes between drives
  • Sensor J 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 jwiring harnessbms

Related codes

P0C8DP0C8EP0C8FP0C90P0C8CP0C96

References: gsi.ext.gm.com, gsi.ext.gm.com.