P0CA9: Hybrid/EV Battery Temperature Sensor M Circuit Range/Performance

P0CA9 reports that sensor M stays within its electrical limits yet disagrees with what the remaining pack sensors measure. GM's 2012 Volt table 12OBDG01A only runs the comparison once drive system, plug-in charging and battery conditioning have rested for over 21,600 s; a spread above 25.3 °C from the mean in 50 of 67 samples is a Type B failure. The 2018 HPC2 table 18OBDG02 uses 25.00 °C at 25 ms sampling and is suspended whenever circuit faults of the sensors or a communication loss with the battery interface module exist. Mitsubishi uses P0CA9 for module sensor [12] of the Outlander PHEV: after more than 3,600 s soak and at pack temperatures from −30 to 60 °C, a deviation of 13 °C or more from the mean of all 50 sensors for 0.32 s sets it. Drift or a loose sensor is typical.

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 appearing after a long parking period
Battery power limited

Most likely causes

Thermistor M drifting while staying in its electrical range
Sensor M lost thermal contact with its module
Module section genuinely warmer or colder, e.g. cooling fault or weak cell

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
Compare the reading with other engine data while varying the engine speed.
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 P0CA9 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
C: Subsystem depends on the code range
A9: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0CA9?

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 P0CA9?

The most common causes are: thermistor M drifting while staying in its electrical range; sensor M lost thermal contact with its module; module section genuinely warmer or colder, e.g. cooling fault or weak cell.

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.