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

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.

High severity. Can I keep driving?If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

Symptoms

Warning lamp that comes and goes between drives
Sensor J value jumping in live data

Most 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

What to check, in order

Start with the simplest. You can tick off each step.

Read the codes with a hybrid-compatible scanner and write down the freeze frame data
Gently move the wiring with the engine running and watch whether the reading changes.
Make sure the battery cooling air intake is clean
Check the 12 V auxiliary battery, which can also trigger warnings
Leave any high-voltage measurements to a specialized repair shop

Good to know

It can trigger limp mode.
It affects emissions.

What each character of P0C91 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
C: Subsystem depends on the code range
91: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0C91?

If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

What causes code P0C91?

The most common causes are: 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.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.